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Evolution of diversity: The Cape flora
Abstract
Although the environmental correlates of plant species richness have long received attention, research into the genesis of this diversity is in its infancy. The recent development of molecular dating methods and the inference of robust phylogenetic hypotheses have made it possible to investigate this problem. I use the Cape flora as a model to show that much modern diversity could be the result of recruiting diverse lineages over the entire Cenozoic into this flora, followed by in situ diversification (thus increasing species richness) of at least some of these lineages over a long period in an environmentally heterogeneous area.
... The climate of the Succulent Karoo is the most arid variant of the South African Mediterranean climate with regular, total, albeit weak winter rains and summer drought (Hilton-Taylor, 1996;Desmet, Cowling, 1999;Burke, 2004;Mucina et al., 2006;Verboom et al., 2009), with fogs as significant factor of maintaining the humidity regime. This climate began to form about 10 mya in the Middle Miocene (Goldblatt, Manning, 2002;Verboom et al., 2009) and was completely formed by the early Pliocene 5 mya (Goldblatt, Manning, 2002;Mucina et al., 2006;Verboom et al., 2009) or perhaps even later, about 3 mya (Linder, 2005). Thus, the duration of the existence of this climate is quite comparable with the average duration of the existence of species and is much shorter than the average duration of the existence of genera (4 and 12 million years, respectively) of animals (Alekseev et al., 2001), whereas taxa of higher plants of the same ranks are considered even more long-lived (Vassiliev, 1965). ...
... Thus, the duration of the existence of this climate is quite comparable with the average duration of the existence of species and is much shorter than the average duration of the existence of genera (4 and 12 million years, respectively) of animals (Alekseev et al., 2001), whereas taxa of higher plants of the same ranks are considered even more long-lived (Vassiliev, 1965). Therefore, traceless extinctions of taxa are unlikely to have taken place during the formation of the modern flora of the Succulent Karoo (see also: Goldblatt, Manning, 2002;Linder, 2005) 14 . Added to that is a great stability of climate of the Succulent Karoo during the Pliocene and even Pleistocene (Goldblatt, 1997; Goldblatt, Manning, 2002;Van der Niet, Johnson, 2009). ...
... (Goldblatt, 1997; Burke, 2005;Linder, 2005;Mucina et al., 2006; Verboom et al., 2009; Potts et al., 2013). Timonin A. C. et al. ...
The geographic characteristic of plant macroevolution is manifested in general in neither even, nor random distribution of the archaic and advanced representatives of a higher taxon in its range. The explanatory concepts proposed are still contradictory. Besides, they are poorly testable, because they concern too long-time intervals during which multiple major changes in both the environment and the ranges of taxa can have occurred; these changes usually continue untraceable in fossil records. The tribe Senecioneae in the Succulent Karoo is best suited for studying the geographic patterns of plant macroevolution for the following reasons: i) the environment of the Succulent Karoo has resulted from unidirectional climate change over 10 million years (accordingly, large fluctuations of the taxon ranges there are highly unlikely); ii) the phylogeny of the tribe Senecioneae is quite fully recognized (and it is not distorted by extinctions, at least at the level of genera); iii) Senecioneae are completely allochthonous in the Succulent Karoo (accordingly, interpretation of results becomes easier and simpler). The archaic genera of Senecioneae are as numerous in the Succulent Karoo as the highly advanced ones, whereas the mid-advanced genera are completely absent there. Such a genus composition of the tribe in the area concerned cannot be explained by the cradle and museum concept, since this area is outside of center of origin/diversification of Senecioneae. The zonal stratification concept is inapplicable to this case, since the climate of the Succulent Karoo was changing unidirectional all the time without noticeable fluctuations. All other concepts proposed are also inapplicable, as they treat the emerging of archaism gradient(s) in the taxon range, but not a deficiency/absence of mid-advanced representatives of a higher taxon in a territory occupied by its archaic and highly advanced members. The absence of mid-advanced members of Senecioneae in the Succulent Karoo could be explained as follows. Any higher taxon very rarely and at long time intervals acquires traits that enable it to spread to areas which greatly differ in their environments from the center of origin/diversification of this taxon. All new subordinate taxa that originate during these time intervals remain confined in the center of origin/diversification of the higher taxon. Accordingly, only archaic and most advanced representatives of this higher taxon would be found faraway its center of origin/diversification.
... A bar with an asterisk indicates the identified distinct shift configuration diversifications (Richardson et al., 2001a;Whitfield and Lockhart, 2007). Species from clade C are largely restricted to southern Africa, especially to the Greater Cape Floristic Region (GCFR), a region in which the flora is characterized by several radiation events (Richardson et al., 2001b;Linder, 2005;Schnitzler et al., 2011). ...
... The current semiarid, winter-rainfall conditions in most of the GCFR started to develop around 10 Ma and became established by the Pliocene, around 5 Ma (Goldblatt and Manning, 2002;Linder, 2003). There is evidence of a drastic increase in diversity across Cape nonsucculent lineages (e.g., Moraea, Pelargonium, Restionaceae) since the middle Miocene, which has been linked to the availability of new niches resulting from the aforementioned climate changes (Linder, 2003(Linder, , 2005Verboom et al., 2009Verboom et al., , 2014. Such species-rich clades seem to have radiated into newly established semi-arid habitats during the late Miocene, particularly in the southwest, whereas no large recent radiations have been reported in the more mesic eastern seaboard of southern Africa (Linder, 2005). ...
... There is evidence of a drastic increase in diversity across Cape nonsucculent lineages (e.g., Moraea, Pelargonium, Restionaceae) since the middle Miocene, which has been linked to the availability of new niches resulting from the aforementioned climate changes (Linder, 2003(Linder, , 2005Verboom et al., 2009Verboom et al., , 2014. Such species-rich clades seem to have radiated into newly established semi-arid habitats during the late Miocene, particularly in the southwest, whereas no large recent radiations have been reported in the more mesic eastern seaboard of southern Africa (Linder, 2005). Crassula is likely to have followed a similar radiation pattern, with more than half of the species in the genus occurring in the (semi-)arid, predominantly winter-rainfall western side of southern Africa (Jürgens, 1995;Manning and Goldblatt, 2012;Snijman, 2013). ...
Premise:
Plants have evolved different ecological strategies in response to environmental challenges, and a higher lability of such strategies is more common in plant groups adapting to various niches. Crassula (Crassulaceae), occurring in varied mesic to xeric habitats, exhibits a remarkable diversity of life forms. However, whether any particular life-form trait has shaped species diversification in Crassula has remained unexplored. This study aims to investigate diversification patterns within Crassula and identify potential links to its life-form evolution.
Methods:
A phylogenetic tree of 140 Crassula taxa was reconstructed using plastid and nuclear loci, and dated based on the nuclear DNA information only. We reconstructed ancestral life-form characters to estimate the evolutionary trends of ecophysiological change, and subsequently estimated net diversification rates. Multiple diversification models were applied to examine the association between certain life forms and net diversification rates.
Results:
Our findings confirm a radiation within Crassula in the last 10 million years. A configuration of net diversification rate shifts was detected, which coincides with the emergence of a speciose lineage during the late Miocene. The results of ancestral state reconstruction demonstrate a high lability of life forms in Crassula, and the trait-dependent diversification analyses reveal that the increased diversification is strongly associated with a compact growth form.
Conclusions:
Transitions between life forms in Crassula seem to have driven adaptation and shaped diversification of this genus across various habitats. The diversification patterns we inferred are similar to those observed in other major succulent lineages, with the most speciose clades originating in the late Miocene. This article is protected by copyright. All rights reserved.
... Indeed, across the plant Tree of Life, high species richness and endemism have been reported for the sclerophyllous 'kwongan' vegetation of much of southwestern Australia (Linder, 2003;Linder et al., 2003;Crisp et al., 2004;Hopper & Gioia, 2004). Similarly, the topographically and geologically diverse Cape region of southern Africa is also noted for its relatively high species richness and endemism, compared to areas of similar size or latitude, and is often dominated by sclerophyllous 'fynbos' vegetation , Linder, 2005Verboom et al., 2009;Manning & Goldblatt, 2012;Linder & Verboom, 2015). A possible explanation for the high species richness in sclerophyllous vegetation is that speciation might be promoted by various environmental drivers, such as fire and nutrient-deficient soils (e.g., Restionaceae), in this vegetation type (Goldberg et al., 2011;Litsios et al., 2014;Mucina et al., 2014). ...
... A possible explanation for the high species richness in sclerophyllous vegetation is that speciation might be promoted by various environmental drivers, such as fire and nutrient-deficient soils (e.g., Restionaceae), in this vegetation type (Goldberg et al., 2011;Litsios et al., 2014;Mucina et al., 2014). Evidence also exists that there has been a varied tempo of diversification, whereby some lineages have rapidly diversified since the Miocene (e.g., Hopper & Gioia, 2004;Verboom et al., 2009), while others have persisted and accumulated species over time (e.g., Linder, 2005;Schnitzler et al., 2011). ...
... A similar shift in climate to drier and cooler occurred with the establishment of the Benguela current near the Miocene/Pliocene boundary in southern Africa, which also would have created suitable conditions for sclerophyllous vegetation (Schnitzler et al., 2011;Manning & Goldblatt, 2012;Linder & Verboom, 2015). It is likely that complex environmental conditions combined with climatic stability after the establishment of the Benguela current are important factors leading to the increased diversification rate of several 'Cape clades' (Linder, 2005;Schnitzler et al., 2011). ...
The predominantly austral genus Schoenus L. is the largest genus in tribe Schoeneae and one of the ten most species‐rich Cyperaceae genera, with over 150 accepted species found mostly in Australia, New Zealand, south‐east Asia and southern Africa. Here we use data based on two nuclear and three plastid DNA regions to present one of the most comprehensive phylogenetic reconstructions of a genus in Cyperaceae to date, covering over 70% of described species of Schoenus. After recent taxonomic realignments in the last four years have both added and removed species from the genus, we show that Schoenus is now monophyletic and is composed of two major clades. In addition, our results indicate that Schoenus originated in Western Australia in the Paleocene and eventually dispersed to surrounding continents, but rarely back. The diversification rate of the genus appears to have slightly decreased over time, and there has not been an increase associated with the establishment of the Cape clade endemic to the sclerophyllous fynbos vegetation type, such as has been reported in other plant lineages endemic to the Cape region. These results will serve as a template to understanding the complex patterns of genome size evolution and to untangle drivers of diversification in this genus.
This article is protected by copyright. All rights reserved.
... Aridification of the western coastline of South Africa and specifically the Namib Desert, can be attributed to the onset of the Benguela upwelling system (BUS), which has been dated to the Miocene and intensified during the Pliocene (Marlow et al. 2000;Diekmann et al. 2003;Krammer et al. 2006;Nicholson 2010;Dupont et al. 2011;Bellstedt et al. 2012). Lineages with an arid origin are thought to contribute only a small proportion of species diversity in the GCFR, even though some of these lineages are speciose, for example Aizoaceae, Arctoteae, and Crassula L. (Linder 2005). The origin of most of these lineages has not been empirically assessed. ...
... Trans-oceanic LDD of Indigofera was rare and appear to have been restricted to the middle and late Miocene. These dates post-date any land bridges or Gondwanan vicariance theories suggested as links between Africa and South America (Tiffney 1985;Sanmartíin and Ronquist 2004;Cronn and Wendel 2004;Linder 2005;Renner et al. 2010;Beaulieu et al. 2013). While northern hemisphere land bridges were still in place around the middle Miocene (Lee et al. 2020), the African-South American link is best explained by LDD based on the absence of Indigofera from Europe and diversity predominantly in South and Central America (Schrire 2005). ...
Indigofera L. is the most diverse genus in the tribe Indigofereae and the third largest genus in the Fabaceae with over 750 species distributed in most tropical to temperate areas of the world. The centre of diversity of the genus lies on the African continent, accounting for over two-thirds of its global diversity. Diversification of Indigofer a’s four main clades began in the Early Miocene, with the Tethyan and Cape Clades having slightly older crown ages than the Pantropical and Paleotropical Clades. Using biogeographical models under a newly assembled, more comprehensively-sampled ITS phylogeny, we confirmed that the tribe Indigofereae originated in the Africa-Madagascar centre, with the genus Indigofera resolving with a mainland African origin c. 38 Mya. Long-distance dispersals were rare, but did occur from Africa to South America and Africa to Australia during the late Miocene. Multiple dispersals from Africa into Asia took place via the arid north-east African and Arabian corridors during the same period. At least four Indigofera dispersals to Madagascar took place during the Miocene. The Cape Clade is a narrowly endemic lineage, mostly restricted to the Greater Cape Floristic Region (GCFR) of southwestern South Africa, while the Tethyan, Pantropical and Paleotropical Clades are more widely dispersed across multiple continents. Both the Cape and Tethyan Clades display strong signals for arid origins in the southern Namib and Richtersveld regions of Southwestern Africa. This study emphasizes the importance of the global Succulent biome in shaping biogeographical patterns of Indigofera globally, particularly in terms of biome conservatism and how it created corridors facilitating trans-continental dispersal.
... It appears that a combination of complex environmental conditions, together with relative climatic stability, promoted high speciation and together with low extinction rates are the most likely reasons for current patterns of megadiversity in the GCFR (Schnitzler et al., 2011). Overall, the evidence suggests that current plant diversity in the region is the product of recruiting diverse lineages over the entire Cenozoic, followed by localized diversification which increased species richness of at least some of the lineages over a long period in an environmentally heterogeneous area (Linder, 2005). ...
... In sum, present-day floral diversity is the cumulative effect of many lineages radiating, perhaps more rapidly than in other areas, over a long period of time, and likely also the result of much topographic and environmental heterogeneity (Linder, 2005). ...
The Greater Cape Floristic Region at the southern tip of Africa is a global megadiversity hotspot. The region's biodiversity has been driven by a long history of topographic, climatic, and sea level change coupled with geological uplift, and without being exposed to any major climate events such as glaciations since the breakup of Gondwana. Among arthropods, this long history has led to the survival of many ancient lineages, manifested by much disparity followed by considerable speciation in more recent times, with the emergence of many cryptic species flocks. There is much convergence among the various taxa and functional groups in how they have responded to the various environmental filters of the past. There has also been the development of a great many morphological, behavioral, and microhabitat specialisms, associated with both topography and particular habitats, as well as interactions with other organisms. Morphological and molecular advances are elucidating how this megadiversity came about. There are indications that among the arthropod fauna, especially species that are small‐sized and have cryptic lifestyles, many more taxa remain to be discovered. Here, we review the eco‐evolutionary trends that have occurred in this region and that have resulted in such remarkable arthropod diversity. Conservation of the arthropod fauna requires recognition of this historical biogeography and ecology. Instigation of approaches over wide areas is required so as to encompass all this diversity.
... Major environmental fluctuations associated with changes in historical climate conditions have shaped ecosystems and influenced the distribution of many species within them (Linder, 2003(Linder, ,2005. These paleoclimatic changes are considered to be the major drivers of many speciation and regional patterns of biodiversity (Linder, 2003(Linder, ,2005Hewitt, 2011;Svenning et al., 2015). ...
... Major environmental fluctuations associated with changes in historical climate conditions have shaped ecosystems and influenced the distribution of many species within them (Linder, 2003(Linder, ,2005. These paleoclimatic changes are considered to be the major drivers of many speciation and regional patterns of biodiversity (Linder, 2003(Linder, ,2005Hewitt, 2011;Svenning et al., 2015). Past climate conditions have often led to contractions and expansions of many species' ranges that, in turn, facilitated reproductive isolation and speciation (Hewitt, 2011). ...
... Electronic copy available at: https://ssrn.com/abstract=4578617 P r e p r i n t n o t p e e r r e v i e w e d a number of taxa are also known to have diverged more frequently during this time, which is thought to be related to the geological stability of the Greater Cape Linder, 2005). ...
... In addition, during the Cenozoic era, bladder grasshoppers diverged on several occasions (Figure 3. (Barraclough, 2006;Cowling et al., 2009;Linder, 2005;Switala et al., 2014;Tolley et al., 2006;Verboom et al., 2009 Thus, with the radiation of flora within the Greater Cape it is possible that pneumorids may have evolved and co-diversified with their respective host plant species. The Greater Cape has been extensively investigated for its angiosperm diversity and diversification, but little is known about the diversification of its insect fauna, although it is assumed that codiversification with the rich flora has occurred (Proches et al., 2009;Colville et al., 2014). ...
... South Africa's CCR is renowned for its exceptional plant diversity, attributed, in part, to a complex mosaic of soil conditions (Linder 2003(Linder , 2005Cowling et al. 2009;Manning and Goldblatt 2012). The region is home to an estimated 764 native legumes, of which 83% are endemic (Manning and Goldblatt 2012), and is also recognised as a hub for exceptionally high endemic rhizobial diversity, with all major rhizobial genera found in the region (Kock 2004;Elliott et al. 2007;Gerding et al. 2012;Hassen et al. 2012;Kanu and Dakora 2012;Beukes et al. 2013;Lemaire et al. 2015, du Preez 2019. ...
... Importantly, Keet et al.'s (2021) study was conducted at similar spatial scales to ours and at sites near ours. Such strong spatial turnover in soil abiotic conditions is characteristic of CCR habitats (Linder 2003(Linder , 2005 and likely impacts both soil microbial (e.g., Keet et al. 2019) and plant (see Ellis et al. 2014) communities. The overall effects of soil type on plant performance that we observed here, therefore, likely reflect major differences in soil abiotic conditions and their knock-on effects on soil microbial communities, between sites. ...
Mutualisms can be disrupted when non-native plants are introduced into novel environments, potentially impacting their establishment success. Introduced species can reassemble mutualisms by forming novel associations with resident biota or by maintaining familiar associations when they are co-introduced with their mutualists. Invasive Australian Acacia species in South Africa have formed nitrogen-fixing rhizobium mutualisms using both pathways.
Here we examined the contributions of novel vs familiar rhizobial associations to the performance of Acacia saligna across different soils within South Africa’s Core Cape Subregion (CCR), and the concomitant impacts of exotic rhizobia on the endemic legume, Psoralea pinnata . We grew each legume with and without Australian Bradyrhizobium strains across various CCR soil types in a glasshouse. We identified root nodule rhizobium communities associating with seedlings grown in each treatment combination using next-generation sequencing (NGS) techniques.
Our results show that different CCR soils affected growth performances of seedlings for both species while the addition of Australian bradyrhizobia affected growth performances of A. saligna , but not P. pinnata . NGS data revealed that each legume associated mostly with their familiar rhizobial partners, regardless of soil conditions or inoculum treatment. Acacia saligna predominantly associated with Australian bradyrhizobia, even when grown in soils without inoculum, while P. pinnata largely associated with native South African Mesorhizobium strains.
Our study suggests that exotic Australian bradyrhizobia are already present and widespread in pristine CCR soils, and that mutualist limitation is not an impediment to further acacia invasion in the region. The ability of P. pinnata to sanction Australian Bradyrhizobium strains suggests that this species may be a good candidate for restoration efforts following the removal of acacias in CCR habitats.
... Whereas during the austral summer, the westerlies and the South Atlantic Anticyclone shift southward limiting the influence of both frontal systems and tropical moisture sources (Reason et al. 2006;Tyson and Preston-Whyte 2000), resulting in warm, dry summer conditions. This Mediterranean-type climatic setting has played an important part in the development of the CFR and is thought to have helped foster the region's botanical diversity (Bradshaw and Cowling 2014;Cowling and Lombard 2002;Cowling et al. 2015;Goldblatt 1978;Linder 2005;Linder et al. 1992). While long-term climatic stability during the Pliocene and Pleistocene is hypothesized to be one of the key factors for the diversification of the Cape flora (Verboom et al. 2014;Cowling and Lombard 2002;Cowling et al. 2015;Cowling et al. 1997;Linder 2005), little direct evidence is available. ...
... This Mediterranean-type climatic setting has played an important part in the development of the CFR and is thought to have helped foster the region's botanical diversity (Bradshaw and Cowling 2014;Cowling and Lombard 2002;Cowling et al. 2015;Goldblatt 1978;Linder 2005;Linder et al. 1992). While long-term climatic stability during the Pliocene and Pleistocene is hypothesized to be one of the key factors for the diversification of the Cape flora (Verboom et al. 2014;Cowling and Lombard 2002;Cowling et al. 2015;Cowling et al. 1997;Linder 2005), little direct evidence is available. Furthermore, species diversity within the CFR is not homogeneous and at finer spatial and temporal scales the concept of climatic stability driving diversity and species richness becomes more complex (Cowling 1992;Cowling and Lombard 2002;Cowling et al. 1997). ...
... Whereas during the austral summer, the westerlies and the South Atlantic Anticyclone shift southward limiting the influence of both frontal systems and tropical moisture sources (Reason et al. 2006;Tyson and Preston-Whyte 2000), resulting in warm, dry summer conditions. This Mediterranean-type climatic setting has played an important part in the development of the CFR and is thought to have helped foster the region's botanical diversity (Bradshaw and Cowling 2014;Cowling and Lombard 2002;Cowling et al. 2015;Goldblatt 1978;Linder 2005;Linder et al. 1992). While long-term climatic stability during the Pliocene and Pleistocene is hypothesized to be one of the key factors for the diversification of the Cape flora (Verboom et al. 2014;Cowling and Lombard 2002;Cowling et al. 2015;Cowling et al. 1997;Linder 2005), little direct evidence is available. ...
... This Mediterranean-type climatic setting has played an important part in the development of the CFR and is thought to have helped foster the region's botanical diversity (Bradshaw and Cowling 2014;Cowling and Lombard 2002;Cowling et al. 2015;Goldblatt 1978;Linder 2005;Linder et al. 1992). While long-term climatic stability during the Pliocene and Pleistocene is hypothesized to be one of the key factors for the diversification of the Cape flora (Verboom et al. 2014;Cowling and Lombard 2002;Cowling et al. 2015;Cowling et al. 1997;Linder 2005), little direct evidence is available. Furthermore, species diversity within the CFR is not homogeneous and at finer spatial and temporal scales the concept of climatic stability driving diversity and species richness becomes more complex (Cowling 1992;Cowling and Lombard 2002;Cowling et al. 1997). ...
... My ago, that is to the Late Miocene. Unlike wet and mild climates of the Early and Middle Miocene that culminated in the Mid-Miocene Climatic Optimum (18-14 My ago), the Late Miocene experienced a trend towards aridification and high seasonality [55] with the advent of winter rains in the south-western Cape. Simultaneously, most of the radiations within the CFR likely took place sometime in the Late Miocene or around Miocene/Pliocene boundary (ca. ...
... It also needs to be borne in mind that the CFR is extremely diversified and embraces a number of distinct vegetation types: from ericoid fynbos, through renosterveld dominated by members of Asteraceae, dry semideserts, to coastal plains, and occasional forests [54,55,59]. Therefore, even though the woody and herbaceous members of the Lefebvrea clade fall into a comparatively narrow and often overlapping range of annual precipitation (ca. ...
Background
One of the major trends in angiosperm evolution was the shift from woody to herbaceous habit. However, reversals known as derived woodiness have also been reported in numerous, distantly related clades. Among theories evoked to explain the factors promoting the evolution of derived woodiness are moderate climate theory and cavitation theory. The first assumes that woody habit evolves in response to mild climate allowing for prolonged life span, which in turn leads to bigger and woodier bodies. The second sees woodiness as a result of natural selection for higher cavitation resistance in seasonally dry environments. Here, we compare climatic niches of woody and herbaceous, mostly southern African, umbellifers from the Lefebvrea clade to assess whether woody taxa in fact occur in markedly drier habitats. We also calibrate their phylogeny to estimate when derived woodiness evolved. Finally, we describe the wood anatomy of selected woody and herbaceous taxa to see if life forms are linked to any particular wood traits.
Results
The evolution of derived woodiness in chamaephytes and phanerophytes as well as the shifts to short-lived annual therophytes in the Lefebvrea clade took place at roughly the same time: in the Late Miocene during a trend of global climate aridification. Climatic niches of woody and herbaceous genera from the Cape Floristic Region overlap. There are only two genera with distinctly different climatic preferences: they are herbaceous and occur outside of the Cape Floristic Region. Therefore, studied herbs have an overall climatic niche wider than their woody cousins. Woody and herbaceous species do not differ in qualitative wood anatomy, which is more affected by stem architecture and, probably, reproductive strategy than by habit.
Conclusions
Palaeodrought was likely a stimulus for the evolution of derived woodiness in the Lefebvrea clade, supporting the cavitation theory. The concurrent evolution of short-lived annuals withering before summer exemplifies an alternative solution to the same problem of drought-induced cavitation. Changes of the life form were most likely neither spurred nor precluded by any qualitative wood traits, which in turn are more affected by internode length and probably also reproductive strategy.
... The climatic setting of the southwestern Cape has played an important part in the development of the vegetation of the Cape Floristic Region (CFR) and is thought to have fostered the region's extraordinary botanical diversity (Goldblatt, 1978;Linder et al., 1992;Cowling and Lombard, 2002;Linder, 2005;Bradshaw and Cowling, 2014;Cowling et al., 2015). While long-term climatic stability during the Pliocene and Pleistocene is hypothesised to be one of the key factors for the diversification of the Cape flora (Cowling et al., 1997(Cowling et al., , 2015Cowling and Lombard, 2002;Linder, 2005;Bergh and Cowling, 2014), little direct evidence is available. ...
... The climatic setting of the southwestern Cape has played an important part in the development of the vegetation of the Cape Floristic Region (CFR) and is thought to have fostered the region's extraordinary botanical diversity (Goldblatt, 1978;Linder et al., 1992;Cowling and Lombard, 2002;Linder, 2005;Bradshaw and Cowling, 2014;Cowling et al., 2015). While long-term climatic stability during the Pliocene and Pleistocene is hypothesised to be one of the key factors for the diversification of the Cape flora (Cowling et al., 1997(Cowling et al., , 2015Cowling and Lombard, 2002;Linder, 2005;Bergh and Cowling, 2014), little direct evidence is available. Furthermore, species diversity within the CFR is not homogeneous, and at finer spatial and temporal scales, the concept of climatic stability driving diversity and species richness becomes more complex (Cowling, 1992;Cowling et al., 1997;Cowling and Lombard, 2002). ...
The southwestern Cape of South Africa is a particularly dynamic region in terms of long-term climate change. We analysed fossil pollen from a 25,000 year sediment core taken from a near-coastal wetland at Pearly Beach that revealed that distinct changes in vegetation composition occurred along the southwestern Cape coast. From these changes, considerable variability in temperature and moisture availability are inferred. Consistent with indications from elsewhere in southwestern Africa, variability in Atlantic Meridional Overturning Circulation (AMOC) was identified as a strong determinant of regional climate change. At Pearly Beach, this resulted in phases of relatively drier conditions (~24–22.5 cal ka BP and ~22–18 cal ka BP) demarcated by brief phases of increased humidity from ~24.5–24 cal ka BP and 22.5–22 cal ka BP. During glacial Termination I (~19–11.7 ka), a marked increase in coastal thicket pollen from ~18.5 to 15.0 cal ka BP indicates a substantial increase in moisture availability, coincident, and likely associated with, a slowing AMOC and a buildup of heat in the southern Atlantic. With clear links to glacial and deglacial Earth system dynamics and perturbations, the Pearly Beach record represents an important new contribution to a growing body of data, providing insights into the patterns and mechanisms of southwestern African climate change.
... The Cape Floristic Region (CFR), found in the southwestern tip of South Africa with ~9000 plant species in only 90,000 km 2 (Cowling et al., 1996;Goldblatt, 1997;Linder, 2003), 70% of which are endemic, is the most diverse extratropical area for plant biodiversity (Latimer et al., 2005;Linder, 2005;Rundel et al., 2016). The CFR is one of several Mediterranean Biomes, where high plant species diversity is typical , yet the southwestern CFR alone is an outlier, with endemism equal to or higher than the neotropics (Latimer et al., 2005;Rundel et al., 2016). ...
... In teasing apart what biotic and abiotic factors impact CFR diversity, there has been much debate on the evolutionary explanations. Some have suggested the high CFR diversity has been the result of historically high speciation rates, followed by re-occurring extinction and colonization (Linder, 2005), a signature of instability within this heterogeneous landscape. Others have postulated that biome stability and topographic heterogeneity maintain species diversity (Colville et al., 2020;Cowling et al., 2005;Potts et al., 2015). ...
As human‐induced change eliminates natural habitats, it impacts genetic diversity and population connectivity for local biodiversity. The South African Cape Floristic Region (CFR) is the most diverse extratropical area for plant biodiversity, and much of its habitat is protected as a UNESCO World Heritage site. There has long been great interest in explaining the underlying factors driving this unique diversity, especially as much of the CFR is endangered by urbanization and other anthropogenic activity. Here, we use a population and landscape genetic analysis of SNP data from the CFR endemic plant Leucadendron salignum or “common sunshine conebush” as a model to address the evolutionary and environmental factors shaping the vast CFR diversity. We found that high population structure, along with relatively deeper and older genealogies, are characteristic of the southwestern CFR, whereas, low population structure and more recent lineage coalescence depicts the eastern CFR. Population network analyses show genetic connectivity is facilitated in areas of lower elevation and higher seasonal precipitation. These population genetic signatures corroborate CFR species‐level patterns consistent with high Pleistocene biome stability and landscape heterogeneity in the southwest, but with coincident instability in the east. Finally, we also find evidence of human land‐usage as a significant gene flow barrier, especially in severely‐threatened lowlands where genetic connectivity has been historically the highest. These results help identify areas where conservation plans can prioritize protecting high genetic diversity threatened by contemporary human activities within this unique cultural UNESCO site.
... Palparidius larvae are psammophilous predators (Mansell, 1999) Toševski, & Emerson, 2013;Hévin et al., 2022;Kergoat et al., 2015;Matenaar, Fingerle, Heym, Wirtz, & Hochkirch, 2018;Meregalli et al., 2021;Price et al., 2019;Sole, Scholtz, Ball, & Mansell, 2013;Talavera, Kaliszewska, Heath, & Pierce, 2020). It has been proposed that the extraordinary diversity found in Southern Africa is the result of both old and more recent radiations (Linder, 2005;Linder, 2008;Schnitzler et al., 2011;Verboom et al., 2009). Persistence of old paleo-endemic taxa ('museum of diversity' model) may have been facilitated by a relative climatic stability throughout the Cenozoic (Cowling, Procheş, & Partridge, 2009), even though a cooling event leading to a more arid climate occurred in the Miocene (Goldblatt & Manning, 2002). ...
... A highly diverse insect fauna is known to be endemic or to have radiated in this region (Hernández-Vera, Caldara, Toševski, & Emerson, 2013;Hévin et al., 2022;Kergoat et al., 2015;Matenaar, Fingerle, Heym, Wirtz, & Hochkirch, 2018;Meregalli et al., 2021;Price et al., 2019;Sole, Scholtz, Ball, & Mansell, 2013;Talavera, Kaliszewska, Heath, & Pierce, 2020). It has been proposed that the extraordinary diversity found in Southern Africa is the result of both old and more recent radiations (Linder, 2005;Linder, 2008;Schnitzler et al., 2011;Verboom et al., 2009). Persistence of old paleo-endemic taxa ('museum of diversity' model) may have been facilitated by a relative climatic stability throughout the Cenozoic (Cowling, Procheş, & Partridge, 2009), even though a cooling event leading to a more arid climate occurred in the Miocene (Goldblatt & Manning, 2002). ...
Palparine and palparidiine antlions constitute an emblematic clade of large and occasionally colourful insects that are only distributed in the western portion of the Eastern hemisphere, with about half of the known species diversity occurring exclusively in southern Africa. Little is known about their evolutionary history, and the boundaries and relationships of most genera are still unresolved. In this study, we analyse a molecular dataset consisting of seven loci (five mitochondrial and two nuclear genes) for 144 antlion species, and provide the first phylogenetic hypothesis for a representative sampling of Palparini and Palparidiini (62 Palparini species, representing 15 of the 17 known genera, and all three known Palparidiini species). In addition, we reconstruct their timing of diversification and historical biogeography. The resulting tree indicates that several extant palparine genera are polyphyletic or paraphyletic and provides interesting leads that ought to be helpful for future taxonomic revisions; it also enables us to re-evaluate the taxonomic utility and relevancy of a number of morphological characters that were previously used to define some genera. Molecular dating analyses indicate that the most recent common ancestor of both groups originated about 92 million years ago (Ma) in the Late Cretaceous. Finally, the results of historical biogeography analyses provide strong support for an origin in southern Africa, which further acted as both a cradle of diversification and a springboard for successive waves of northern dispersals.
... Such farmlands support species that are adapted to these disturbances (Batáry et al. 2020) and are more prone to utilise crop fields. In contrast, fynbos patches in the CFR are true remnants that have been relatively undisturbed both through historical and recent times (Linder 2005). Furthermore, many arthropod groups in fynbos are highly adapted to the local vegetation and have developed specialist relationships with the plants (Augustyn et al. 2013), likely driving these strong affiliations. ...
Edges between adjacent biotopes may hinder or promote spillover of arthropods, influencing their distribution across landscapes. An understanding of spillover between natural and production areas enables management of edge effects for optimal biodiversity conservation. We assessed arthropod assemblages across vineyard-fynbos edges in the Cape Floristic Region of South Africa, where biodiversity-rich fynbos often borders vineyards. Species richness, assemblage composition, and compartmentalised beta-diversity (species turnover and nestedness) were assessed for three vegetation layers (ground level, lower vegetation, and upper vegetation) to determine bidirectional spillover. Species were also categorised according to biotope affiliation (crop-associated, fynbos-associated, or ubiquitous), based on habitat fidelity. We assessed how species richness of each biotope affiliation was influenced by environmental and management variables. Our main interest was biotope-specific variables which may enhance or impede spillover by influencing arthropods affiliated with the opposite biotope. Arthropod species richness did not differ along vineyard-fynbos transects for ground and lower vegetation layers but was lower in the upper vineyard vegetation compared to fynbos. Arthropod assemblages were distinct between biotopes for upper and lower vegetation but were similar on the soil surface and showed lower nestedness differences, indicating greater spillover by ground-level arthropods. In vineyards, no variables influenced fynbos-associated species, although herbaceous vegetation cover promoted ubiquitous arthropod species richness. Spillover between the biotopes was limited, and no drivers could be identified that promote spillover into vineyards, yet both biotopes supported diverse and distinct arthropod assemblages. Therefore, conservation of natural fynbos patches alongside sensitively managed vineyards is feasible for harmonising biodiversity conservation and viticulture.
... Natural fynbos is highly diverse and inherently complex compared to semi-natural vegetation where historical disturbances have simplified natural complexity. Fynbos patches in these agricultural landscapes are true remnants that have been relatively undisturbed both through historical and recent times (Linder 2005). With the inclusion of semi-natural features, our estimate is 32.83%, putting all our sites at the higher end of the complexity spectrum, compared to most studies. ...
Understanding the effects of agricultural practices on farmland biodiversity requires a landscape perspective, as local-scale processes can be influenced by the structure of the surrounding landscape. We assess whether amount of natural vegetation in the landscape interacts with two local-scale variables, in-crop vegetation cover and farming approach (organic vs. integrated), to influence vineyard arthropods within the Cape Floristic Region. Responses were assessed for overall arthropods and three sub-categories based on arthropod species affinity to vineyards, natural vegetation (fynbos), or both systems. There were no significant interactions between local and landscape variables that affected the species richness of arthropods. However, there was a main effect of increased in-crop herbaceous vegetation that increased the species richness of overall arthropods and ubiquitous arthropods. Furthermore, interactions between the amount of natural vegetation and local-scale processes influenced composition of arthropod assemblages. Assemblages among integrated vineyards were similar in composition irrespective of landscape context, whereas they were dissimilar among organic vineyards in landscapes with different levels of natural vegetation. Our results suggest a relatively lower homogenising effect of organic farming than non-organic farming on landscape-scale biodiversity and that maintaining non-crop vegetation in vineyards benefits arthropod diversity. These findings emphasise the importance of considering the interplay between local management and the surrounding landscape in promoting biodiversity in a farming and conservation mosaic. This is especially important where landscapes vary greatly in complexity, as in many agricultural regions worldwide.
... During the Pleistocene, the suggested relative stability of rainfall regimes possibly reduced the risk of extinction of species and populations (Potts et al., 2013). The high levels of environmental and topographical heterogeneity of the CFR (Cowling & Lombard, 2002;Linder, 2005;Procheş et al., 2009;van Santen & Linder, 2020;Verboom et al., 2015) effectively translate into diverse ecological niches that favoured the evolution of numerous endemic plant lineages with narrow ranges and poor dispersal abilities (Dynesius & Jansson, 2000;Linder, 2003). The oldest plant radiations likely occurred in mountain ranges whereas most recent radiations were hypothesized to have occurred more recently during the Pleistocene (Grobler & Cowling, 2021;Linder, 2008;Linder & Hardy, 2004;Verboom et al., 2009). ...
The Cape Floristic Region in the Republic of South Africa is a well-recognized hotspot of biodiversity. Although this region is mostly known for its high level of plant diversity and endemicity, it also hosts an understudied and likely diverse arthropod fauna. Here we investigate the evolutionary history and timing of diversification of the apterous weevil genus Phlyctinus (Curculionidae: Entiminae), which is endemic to the coastal area and adjacent mountain ranges of the Cape floristic region and generally associated with sunflower plants (Asteraceae). We use a diverse array of molecular analyses (phylogenetic inference, molecular species delimitation and dating analyses) to analyse a novel molecular dataset of 202 weevil specimens (including 170 Phlyctinus sampled in 60 sites), and sequenced for two mitochondrial and four nuclear gene fragments. Phylogenetic and dating analyses indicate that the genus started diversifying in the late Miocene, with contrasting diversification dynamics for the three inferred clades, which present disjunct distributions. Host plant records and the lack of relatedness of species living in sympatry indicate that the diversification of Phlyctinus was predominantly driven by allopatric (geographic) speciation. We hypothesize that the interplay between topography and recurring cycles of coastline-habitat fragmentation resulting from sea level oscillations spurred the diversification of the most speciose clade, whereas in the two remaining clades populations likely remained connected thus hampering allopatric speciation. Interestingly, this pattern echoes with the role of sea level oscillations as an important driver of the radiation of several lineages in the coastline ecosystems of the Cape Floristic Region.
... The level of trait diversity in these fynbos areas is likely a good benchmark for historical functional diversity. Schuldt et al. (2014) showed an increase in functional diversity in more species-rich and older stands of woody plants, as is the case for fynbos which is hyper-diverse and ancient with little historical, and more recent, disturbances (Linder, 2005). Functional diversity is directly related to ecosystem functioning (Mouillot et al., 2011), indicating that farmers may benefit from consequent services that spiders and beetles provide e.g., predation of pest species. ...
Agriculture is a major contributor to habitat transformation, homogenising biological communities, and reducing biodiversity at local and regional scales. Over time, biotic homogenisation causes regional biotas to become genetically, taxonomically, and functionally similar, impacting the functioning and resilience of natural and agricultural systems. Here, we assessed alpha and beta diversity, trait diversity, and trait composition of spider and beetle assemblages in biodiversity-friendly vineyards and natural fynbos vegetation (a low-growing sclerophyllous vegetation type) in the Cape Floristic Region biodiversity hotspot to evaluate the influence of viticulture on large-scale patterns of arthropod diversity. Transects spanning from vineyards into fynbos were used to analyse differences in arthropod assemblages between the two biotopes. Spider species richness was significantly higher in fynbos compared to vineyards, but both systems supported relatively high spider and beetle alpha diversity. Spider beta diversity did not differ between the systems, but beetle beta diversity was significantly lower in vineyards. This difference was due to a lower level of assemblage nestedness, whereas beetle species replacement was similar in vineyards and fynbos. Only spider trait richness and beetle trait divergence were significantly lower in vineyards compared to fynbos. Assemblage composition of both taxonomic groups differed between biotopes, due to different species trait associations with each biotope. Plant-dwelling spiders and small-bodied beetles were strongly positively associated with fynbos, and predatory beetles with vineyards. Common spiders and predatory beetles were strongly negatively associated with fynbos. Our results indicate that vineyards support high arthropod diversity when compared to the natural vegetation. This supports the concept that sensitively managed agroecosystems can maintain species-rich assemblages at different spatial scales.
... The Greater Cape Floristic Region (GCFR) of South Africa (Born et al., 2006) is a region of outstanding vascular plant richness and includes two of the 25 global biodiversity hotspots (Myers et al., 2000). One of the major drivers of this diversification is pollinator specialisation (Johnson, 1996;Linder, 2005;Pirie, 2011;Pirie, 2016), specifically amongst plants of the mesic Core Cape Floristic Region (Manning and Goldblatt, 2012), which reflects the pattern of pollinator-driven diversification of the southern African flora (Johnson, 2010). Although the link between pollinators and the diversification of the flora in the Core Cape Floristic Region has been explored, less is understood about this relationship in the more arid, northern parts of the GCFR, the "Extra Cape Flora" or Succulent Karoo Region (Snijman, 2013). ...
Pollinator specialisation is one of the major drivers of angiosperm diversification in the Greater Cape Floristic Region (GCFR) of South Africa. Conophytum (Aizoaceae) is a flagship genus for the underexplored arid regions of the GCFR (ca. 108 spp.) with 83.9% of its species endemic to this region and has a floral structure that is unique within the rapidly diversified Ruschieae (Aizoaceae). Floral traits, together with leaf characters divide the genus into 16 sections. We present here the first phylogenetic hypothesis for Conophytum, based on molecular data. The combined phylogenetic data for six plastid regions (matK, rpl16, rps16, trnL-F, trnQ-rps16 and trnS-trnG) were analysed using Bayesian inference, maximum likelihood and maximum parsimony to test the evolution of this floral diversity and current sectional classification. Conophytum was recovered as monophyletic including the three small genera Berrisfordia L.Bolus, Herreanthus Schwantes and Ophthalmophyllum Dinter & Schwantes. Six strongly supported clades were recovered within Conophytum: while several of the sections were broadly retrieved within these clades, the more morphologically variable sections such as Minuscula and Wettsteinia were not supported by our data. The distributions of the six clades largely overlap and are generally confined to the arid parts of the GCFR within South Africa, with only one clade extending into the southern wetter parts. Ancestral character reconstructions showed that floral traits evolved multiple times with low phylogenetic signal recovered for autumn- and winter-flowering and flower type, while the other traits indicated no phylogenetic signal. This lack of phylogenetic signal suggests that drivers of diversity in Conophytum are possibly linked to adaptation to pollinators, with a high rate of inferred pollination shifts observed, i.e. 1.7 shifts per species, mirroring that of Lapeirousia (Iridacaeae) in the GCFR. The evolution of unique tubular flowers and shift to autumn-flowering were recovered as traits indicating strong phylogenetic signal and may have enabled Conophytum to exploit a range of pollinators through diversification in floral morphologies.
... Both tribe Schoeneae and the southern African Schoenus have relatively high species richness in the Cape region of southern Africa (Verboom, 2006;Viljoen et al., 2013;Elliott et al., 2021). This region is noted for its relatively high species endemism, richness and turnover compared with areas of similar size or latitude, possibly a result of various drivers such as nutrient-deficient soils and rapidly changing topography (Linder, 2005;Manning and Goldblatt, 2012;Linder and Verboom, 2015). We first examine patterns of genome size and chromosome number variation in tribe Schoeneae. ...
Background and aims:
It is unclear how widespread polyploidy is throughout the largest holocentric plant lineage-the Cyperaceae. Because of the prevalence of chromosomal fusions and fissions which affect chromosome number but not genome size, it can be impossible to distinguish if individual plants are polyploids in holocentric lineages based on chromosome count data alone. Furthermore, it is unclear how differences in genome size and ploidy levels relate to environmental correlates within holocentric lineages, such as the Cyperaceae.
Methods:
We focus our analyzes on tribe Schoeneae, and more specifically, the southern African clade of Schoenus. We examine broad-scale patterns of genome size evolution in tribe Schoeneae and focus more intensely on determining the prevalence of polyploidy across the southern African Schoenus by inferring ploidy level with the program ChromEvol, as well as interpreting chromosome number and genome size data. We further investigate whether there are relations between genome size / ploidy level and environmental variables across the nutrient-poor and summer-arid Cape biodiversity hotspot.
Key results:
Our results show a large increase in genome size, but not chromosome number, within Schoenus compared to other species in tribe Schoeneae. Across Schoenus, there is a positive relation between chromosome number and genome size, and our results suggest that polyploidy is a relatively common process throughout the southern African Schoenus. At the regional scale of the Cape, we show that polyploids are more often associated with drier locations that have more variation in precipitation between dry and wet months, but these results are sensitive to the classification of ploidy level.
Conclusions:
Polyploidy is relatively common in the southern African Schoenus, where a positive relation is observed between chromosome number and genome size. Thus, there can be a high incidence of polyploidy in holocentric plants, whose cell division properties differ from monocentrics.
... The fynbos represents one of the most remarkable global floral biodiversity 'hotspots' , characterized by unique species richness and endemism, with over 9,000 recorded plant species restricted to a small geographic area (±90,000 km 2 ), of which almost 70% are endemic 77 . Much of this diversity is due to a handful of speciose clades (the 'Cape floral clades') that, including Phylica 31,78,79 , have traditionally been regarded as having radiated within the Cape 31,78,79 . Geological studies and fossil evidence [80][81][82][83][84] indicate a Gondwanan origin for the diverse biota in Myanmar ambers, but two alternative pathways for its transport to Myanmar, either via the West Burma Block or the Indian Plate, were possible 80 . ...
The rapid Cretaceous diversification of flowering plants remains Darwin’s ‘abominable mystery’ despite numerous fossil flowers discovered in recent years. Wildfires were frequent in the Cretaceous and many such early flower fossils are represented by charcoalified fragments, lacking complete delicate structures and surface textures, making their similarity to living forms difficult to discern. Furthermore, scarcity of information about the ecology of early angiosperms makes it difficult to test hypotheses about the drivers of their diversification, including the role of fire in shaping flowering plant evolution. We report the discovery of two exquisitely preserved fossil flower species, one identical to the inflorescences of the extant crown-eudicot genus Phylica and the other recovered as a sister group to Phylica, both preserved as inclusions together with burned plant remains in Cretaceous amber from northern Myanmar (~99 million years ago). These specialized flower species, named Phylica piloburmensis sp. nov. and Eophylica priscastellata gen. et sp. nov., exhibit traits identical to those of modern taxa in fire-prone ecosystems such as the fynbos of South Africa, and provide evidence of fire adaptation in angiosperms.
... The Cape Floristic Region (CFR) of South Africa is a biodiversity hotspot, a home to over 6.000 endemic species (Goldblatt and Manning, 2002;Linder, 2005), in which habitat loss is a major threat to biodiversity. About 3.185 plant species are of conservation concern in the CFR (Rouget et al., 2014), especially in the critically endangered renosterveld which is one of the most threatened habitat types in the fynbos biome of the CFR (Newton and Knight, 2005;Esler et al., 2014;Topp and Loss, 2019). ...
Habitat fragmentation – in terms of a combination of habitat loss and separation – is a major threat to the renosterveld of the Cape Floristic Region (CFR) of which 85% has been transformed, mostly for agriculture. The effects thereof has not been well studied, in particular in the Eastern inland areas. In this study we seek to understand how habitat patch size influence visitation rate of pollinators of winter flowering plants in the Eastern-Rûens Shale Renosterveld of the Overberg region. We compared pollinator visitation rates to flowers of Relhania garnotii, Clutia sp. nov and Oxalis purpurea between small (0–4.9 ha) and medium (5–15 ha) sized fragments, and compared these to the last large intact protected area, the Haarwegskloof Renosterveld Reserve (>500 ha), termed mainland. We classified degree of isolation among fragments into high (>100 m) and low (<100 m) based on the distance between the outer edge of a fragment to its surrounding fragments and compared pollinator visitation rates between the two levels of isolation. Furthermore, we compared seed set of Bobartia longicyma and Trichodiadema strumosum between fragments and the mainland. We recorded 442 plant-pollinator interactions over a total of 75 h of observation. Pollination rate was significantly higher in fragments compared to the mainland. Within fragments, pollination rate and species richness were significantly higher in medium-sized fragments compared to small fragments. The degree of isolation had a negative effect on pollinator visitation rates among habitat patches, with lower visitation rates and pollinator species richness recorded in fragments with higher degree of isolation, supporting the Habitat Amount Hypothesis (HAH). Plant species exhibited a strong reliance on pollinators for reproduction but were not pollen-limited in either the fragments or mainland. These results indicate that the effect of fragmented habitats do not necessarily affect pollination rates of a certain size of habitat patches, but beyond an undefined threshold, pollinator rates decrease significantly. While in very small fragments ecosystem functions might be declining, in this study insect species have been observed in the smaller fragments that only occurred there, which indicates that heterogeneity of habitat fragments could offer ecological benefits. This highlights the importance of preserving fragments, as an important part of maintaining the remaining renosterveld. Therefore, conservation efforts should be enhanced to also preserve the small fragments that may serve as stepping stones for pollinators in the fragmented renosterveld.
... The CCFR À one of the richest biodiversity hotspots in the world À is home to over 9300 plant species (Linder 2005;Manning 2002, Manning andGoldblatt 2012), 68% of which are endemic to the region (Manning and Goldblatt, 2012). Most of the flowering plants in the fynbos biome of the CCFR depend on fire at specific intervals for reproduction (Bond and van Wilgen, 1996). ...
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The influence of invasive alien plants on plant community structure and above ground biomass in their novel range is poorly understood, as the magnitude and direction of these effects are often species and ecosystem specific. Here we compared community metrices of native plants and soil properties between study sites invaded by Hakea drupacea, uninvaded sites and cleared sites (sites formerly invaded by H. drupacea). A total of 129 plant species belonging to 75 genera were recorded across all study sites. Invasive Acacia saligna, A. longifolia, A. cyclops (Fabaceae) and Leptospermum laevigatum (Myrtaceae) co-occurred with H. drupacea in the invaded sites. Overall plant species richness, which constituted higher number of native plant species, was recorded in uninvaded sites compared to invaded and cleared sites. Plant species composition was similar between uninvaded and cleared sites, but species composition recorded in uninvaded and cleared sites were significantly different from species composition recorded at invaded sites. Litter depth was significantly higher in invaded sites compared to uninvaded and cleared sites. Hakea drupacea did not affect soil properties in invaded sites. Here we show that H. drupacea probably reduces the diversity of native plant species especially in invaded sites probably through the effect of litter production and canopy cover, pointing to a beneficial effect of removal of H. drupacea. We encourage active restoration of sites invaded by H. drupacea at early stages of invasion before the plants become established and suppress the growth of native species.
... When upscaling geographic isolation to large land masses and on the long-term, that is, 100 million years, evolution also leads to important endemism but at a slower more constant rate, and it does not necessarily promotes exceptional richness in the process (Brooks et al. 2006). The unique mammal fauna present in the Australian hotspots and the rare flora of the Cape Floristic Province constitute excellent examples of such in-situ processes (Linder 2005;Hopper et al. 2016). ...
... Nectar feeders were filled with a colourless 1:4 sugar to water solution (Images by Monique du Plessis). hotspot with thousands of endemic plant species (Holmes et al., 2012;Linder, 2005). Experiments took place in 18 gardens (17 for flower visitation experiments) across four suburbs (Scarborough, Simon's Town, Glencairn and Clovelly; Fig. 1), at least four kilometres apart, and where nectar feeders are often used (Coetzee et al., 2018). ...
Globally, people feed wild animals to interact with nature. Attracting nectarivorous birds to gardens using artificial nectar feeders is increasingly popular, yet little is known about its influence on birds and the plants they pollinate. We investigated effects of nectar feeders on African birds and their plant mutualists, by conducting feeding experiments in gardens and natural vegetation along the suburban edge of the Cape Peninsula, South Africa. We compared relative abundance and local distribution patterns of nectar-specialist, nectar-opportunist and non-nectarivore bird species between feeder and control treatments. We then tested whether nectar feeders in gardens affected visitation rates to two sunbird-pollinated Erica species in neighbouring vegetation compared to control sites. Nectar feeders increased the density of nectarivores (but not non-nectarivores) in gardens but decreased their density in neighbouring vegetation, even in winter when floral abundance was high. These changes in sunbird distribution patterns had no detectible influence on visitation rates to E. abietina, but decreased visitation to E. plukenetii flowers by on average 16% at least up to 300 m of gardens with feeders. Thus, although supplementary nectar feeding may have conservation value for nectarivorous birds by reducing their urban sensitivity, it can inadvertently interfere with bird-plant pollination networks by competing with native flowers for birds’ attention.
... The diversity of flora in a particular geographic area is determined by climatic, geological, soil, orographic conditions and depends on the intensity of historical and current human activities (Linder, 2005;di Marco & Santini, 2015). Although studies on the flora, as an assemblage of plant taxa in a specific geographic area, have received less attention worldwide in recent decades, they are an essential part of knowledge about biodiversity. ...
Information on the occurrence of Eleocharis ovata (Cyperaceae) in Lithuania for a long time had been based on misidentified specimens only. During the studies on the flora of South Lithuania in 2020, we discovered this species in Varėna district on the shores of Lake Pabezninkai. We performed field investigations on the distribution,
size of population and habitats of E. ovata from August to October 2020 on the shores of Lake Pabezninkai and, searching for this species, surveyed potential habitats on the shores of eight other lakes in South Lithuania. A total of 63 individuals of E. ovata were found on the shores of Lake Pabezninkai, and they were widely dispersed
on the northern and south-western shores of the lake. Most of the registered individuals of E. ovata were found growing on wet sand and mud in the communities of the Isoëto-Nanojuncetea class. Solitary individuals were also found in communities of the Phragmito-Magnocaricetea class. Assessment of E. ovata according to the IUCN criteria revealed that this species, currently occurring at a single locality in Lithuania, should be classified as critically endangered (CR). Conservation of E. ovata and other rare plant species recorded on the
shores of Lake Pabezninkai should be organised by maintaining favourable habitat conditions.
... So, why is biogeography important to biogeochemistry in the 21st century? As Linder (2005) points out, understanding how the distribution of organisms across the planet came to be, can only be achieved by understanding how lineages diversify. Moreover, using newly emerging molecular systematics in recent decades will be key in understanding current and future organismal range expansions driven by global change (e.g. ...
The evolution of biogeochemistry, retraces the important historical steps in part, covered by Gorham (Biogeochemistry 13:199–239, 1991) in the 18–19th centuries—with new emergent linkages and trends in 20–21st centuries. In the post-phlogiston period, key synthetic connections are made between weathering, atmospheric chemistry, carbon cycling, and climate change. Early work in the 19th century, focused on weathering and the importance of organisms in the exchange of carbon dioxide between the rocks and the atmosphere, provided foundations for new analytical approaches. The role microbes in connecting abiotic and biotic processes begins to emerge, based largely on the existing knowledge of stoichiometry in agricultural soils and plants. This in part, leads to the founding of ecology and its linkages with evolution and biogeography. Verandsky boldly emerges in the 20th century, with his concepts of a biosphere and a noosphere, as concerns begin to arise about human impacts on nature. The development of organic geochemistry as a discipline, allowed for new roots to develop in the evolution of biogeochemistry through linkages between short and long-term carbon cycles. In the 20th century, a new interesting stoichiometry emerges in biogeochemistry—as related to the Green Revolution, human population growth, and eutrophication problems. The advent of long-term and large-scale experiments help to constrain the complexity of non-linearity and regional differences in fluxes and rates in biogeochemical work. A new age begins in the 21st century whereby molecular approaches (e.g. omics) combined with large-scale satellite, monitoring, survey, observatory approaches are combined in the development of Earth System models. These new connections with ecological/evolutionary genetics are one of the more dramatic and important aspects of biogeochemistry in modern times.
... Geographical isolation is one of the key drivers of species diversification in both islands (Heaney, 2000;Rosindell & Phillimore, 2011;Whittaker & Fernández-Palacios, 2007) and continents (Linder, 2005;Pennington et al., 2010;Rieseberg & Willis, 2007). Mechanisms by which isolation promotes evolutionary divergence include founder effects and genetic drift (non-adaptive speciation; Rundell & Price, 2009). ...
Aims
The General Dynamic Model of oceanic island biogeography (GDM) predicts how biogeographical rates, species richness, and endemism vary depending on island age, area, and isolation, based on the interplay of colonization, extinction, and speciation. Here, we used a simulation model to test whether GDM predictions may arise from individual- and population-level processes.
Location
Hypothetical hotspot islands.
Methods
Our model (i) considers an idealized island ontogeny, (ii) metabolic constraints, and (iii) stochastic, spatially-explicit, and niche-based processes at the level of individuals and populations (plant demography, dispersal, competition, mutation, and speciation). Isolation scenarios involved varying dispersal ability and distances to mainland.
Results
Humped temporal trends were obtained for species richness, endemic richness, proportion of cladogenetic endemic species, number of radiating lineages, number of species per radiating lineage, and biogeographical rates. The proportion of anagenetic endemics and of all endemics steadily increased over time. Extinction rates of endemic species peaked later than for non-endemic species. Species richness and the number of anagenetic endemics decreased with isolation as did rates of colonization, anagenesis, and extinction. The proportion of all endemics and of cladogenetic endemics, the number of cladogenetic endemics, of radiating lineages, and of species per radiating lineage, and the cladogenesis rate all increased with isolation.
Main conclusions
The results confirm most GDM predictions related to island ontogeny and isolation, but predict an increasing proportion of endemics throughout the experiment: a difference attributable to diverging assumptions on late island ontogeny. New insights regarding the extinction trends of endemics further demonstrate how simulation models focusing on low ecological levels provide tools to test biogeographical-scale predictions and to develop more detailed predictions for further empirical tests.
... This Mediterranean climate region is known for warm, dry summers and cool, wet winters, with nutrient-poor, acidic soils Van Wilgen et al., 1996;Richards et al., 1997;Cowling et al., 2003). The rich flora in this region has diversified across a heterogeneous landscape, occupying narrow niches at times (Linder, 2005), and in general, well adapted to survive these harsh conditions (Lambers et al., 2011). Endemic to the CFR is the commercially important plant, Aspalathus linearis (Burm. ...
Aspalathus linearis is a commercially important plant species endemic to the Cape Floristic Region of South Africa and is used to produce a herbal tea known as rooibos tea. Symbiotic interactions between A. linearis and soil bacteria play an important role in the survival of Aspalathus plants in the highly nutrient-poor, acidic fynbos soil. The aim of this study was to characterize and compare rhizosphere and bulk soil bacterial communities associated with natural and commercially grown A. linearis, as well as the effect of seasonal changes on these communities. Bacterial communities were characterized using high throughput amplicon sequencing, and their correlations with soil chemical properties were investigated. The N-fixing bacterial community was characterized using terminal restriction fragment length polymorphism and real time quantitative polymerase chain reaction. Actinobacteria, Proteobacteria, and Acidobacteria were the most dominant bacterial phyla detected in this study. Highly similar bacterial communities were associated with natural and commercially grown plants. Significant differences in the bacterial community were observed between rhizosphere and bulk soils collected in the dry season, while no significant differences were detected in the wet season. This study provides insights into bacterial community structure and potential factors shaping bacterial community structure with commercially important A. linearis.
... Like in fynbos (Linder, 2005) and campos rupestres (Abrahão et al., 2019), plant species in south-western Australia have evolved adaptations to the severely nutrient-impoverished soils, which are especially low in soil phosphorus (P), via a range of nutrientacquisition strategies (Lambers, Brundrett, Raven, & Hopper, 2010). In particular, Proteaceae have evolved mechanisms that allow them to acquire scarcely available soil P through carboxylate exudation from cluster roots (Shane & Lambers, 2005). ...
Hundreds of Proteaceae species in Australia and South Africa typically grow on phosphorus (P)‐impoverished soils, exhibiting a carboxylate‐releasing P‐mobilizing strategy. In the Southwest Australian Biodiversity Hotspot, two Xylomelum (Proteaceae) species are widely distributed, but restricted within that distribution.
We grew Xylomelum occidentale in hydroponics at 1 μM P. Leaves, seeds, rhizosheath and bulk soil were collected in natural habitats.
Xylomelum occidentale did not produce functional cluster roots and occupied soils that are somewhat less P‐impoverished than those in typical Proteaceae habitats in the region. Based on measurements of foliar manganese concentrations (a proxy for rhizosphere carboxylate concentrations) and P fractions in bulk and rhizosheath soil, we conclude that X. occidentale accesses organic P, without releasing carboxylates. Solution ³¹P‐NMR spectroscopy revealed which organic P forms X. occidentale accessed.
Xylomelum occidentale uses a strategy that differs fundamentally from that typical in Proteaceae, accessing soil organic P without carboxylates. We surmise that this novel strategy is likely expressed also in co‐occurring non‐Proteaceae that lack a carboxylate‐exuding strategy. These co‐occurring species are unlikely to benefit from mycorrhizal associations, because plant‐available soil P concentrations are too low.
Synthesis. Our findings show the first field evidence of effectively utilizing soil organic P by X. occidentale without carboxylate exudation and explain their relatively restricted distribution in an old P‐impoverished landscape, contributing to a better understanding of how diverse P‐acquisition strategies coexist in a megadiverse ecosystem.
... South Africa has two biodiversity hotspots, the Cape Floristic Region and Succulent Karoo (Myers et al., 2000). Some floral diversity of these hotspots dates back to the Oligocene, but most modern lineages appear to have diversified in response to progressive aridification that occurred during the late Miocene and the Pliocene-Pleistocene (Midgley et al., 2001;Richardson et al., 2001;Klak et al., 2004;Linder, 2005). While late Neogene cli-mate change apparently provided the ideal setting for cladogenesis within floral assemblages, processes of divergence among the vertebrate fauna remain poorly understood. ...
The phylogeographic structure of the monotypic endemic southern African angulated tortoise Chersina angulata was investigated throughout its distribution with the use of partial sequences from three mtDNA loci (COI, cyt b and ND4). Phylogeographic and phylogenetic structuring obtained for the three-mtDNA markers were highly congruent and suggested the presence of two genetically distinct, reciprocally monophyletic evolutionary lineages. Group one contained two subclades with haplotypes from the northwestern Cape and southwestern Cape, while haplotypes from the southern Cape comprised group two. These two major clades were separated by nine and eight mutational steps for both COI and ND4, respectively. Of the three-mtDNA gene regions examined, the ND4 partial sequence contained the most phylogenetic signal. Haplotype diversity was generally low and we recovered 34 haplotypes for the 125
... Second, the comparison of phylogenetic diversity metrics between clades would be invalid if all clades were in effect assigned the same age, as performed here (i.e., all root ages assigned a value of 1.0), which they are evidently not (e.g., refs. 38,49,74). Third, embedding all 21 Cape clades in a flora-wide tree allows us to compile overall phylogenetic diversity metrics for all clades and account for their deep history, which is particularly important in the case of phylogenetic beta diversity because the age of a group will significantly affect turnover in branch lengths (i.e., shallow vs. deep branches). ...
Significance
What explains global patterns of diversity—environmental history or ecology? Most studies have focused on latitudinal gradients—the decline of diversity from the tropics to the poles. A problem with this is that it conflates predictions of historical and ecological hypotheses: The productive tropics have also experienced high Cenozoic biome stability. Longitudinal diversity gradients can overcome this constraint. We use a longitudinal diversity gradient in the megadiverse Cape Floristic Region to model species and evolutionary diversity in terms of Pleistocene climate stability and ecological heterogeneity. We find that biome stability is the strongest predictor of diversity measures, and argue that stability, in conjunction with measures of ecological opportunity—other than productivity—may provide a general explanation for global diversity patterns.
... Non-equilibrium explanations for MTE diversity typically involve one or more of three scenarios: 1) there has been a greater time for lineages to accumulate diversity in MTEs because these regions are older than other temperate biomes ("time for speciation"); 2) MTEs have had reduced extinction rates (Hopper 2009;Hopper et al. 2016); or 3) MTE lineages or environments have features that have promoted increased speciation rates (Hopper and Gioia 2004;Linder 2005;Sauquet et al. 2009;Schnitzler et al. 2011;Reyes et al. 2015). After rainforests, the Mediterranean biome may be the oldest of Australia's biomes, with recent estimates suggesting the development of a Mediterranean type climate from 30Mya (Lamont and He 2017), whereas temperate forests probably did not become widespread until 25-15Mya (Byrne et al. 2011), and modern woodland, grassland, savannah, and arid ecosystems until 8-3Mya (Hill 2004;Beerling and Osborne 2006;Byrne et al. 2008;Bowman et al. 2010;Andrae et al. 2018). ...
The form, function, and kinds of species that coexist together vary dramatically from place to place. These spatial patterns of biodiversity are the focus of biogeographical and macroecological research and offer us clues into the evolutionary processes shaping nature's variety. Finding general patterns and their underlying drivers, however, is not a straightforward task because a suite of ecological and evolutionary processes interact to shape patterns of biodiversity in the present-day. By integrating geographic, phylogenetic, phenotypic, and ecological data, and methods from the tool kits of community ecologists, macroevolutionists, and biogeographers, we can delve into the complexities shaping diversity patterns and get a more holistic understanding of their origin and maintenance. In my opening chapter I briefly summarise the state of the field and introduce the outline of my thesis. The first two chapters forming the core of my thesis (Chapter Two and Chapter Three) present new methods to study spatial patterns of biodiversity. Chapter Two presents a process-based model of geographic range evolution and the geography of speciation. I use this model to make inferences about the history of speciation in thirty different plant and animal clades, highlighting some general taxonomic trends in speciation which have shaped biogeographic patterns in the present day. Then, in Chapter Three, I present a method to reconstruct temporal patterns in the evolution of biodiversity based on ancestral range estimates from historical biogeographic models. The following three chapters present empirical studies which link community ecology, macroecology, and macroevolution to better understand spatial diversity patterns in plants and lizards. Chapter Four integrates phenotypic and spatial data to look at what drives global patterns of species richness in ten different lizard clades, comprising over 6000 species. Chapter 5 and Chapter 6 explicitly investigate links between community ecology and macroevolution to look at the evolution of the Southwest Australian Biodiversity Hotspot flora, using a large genus of Australian plants, Hakea (family Proteaceae), as a case study. Chapter Five focuses on how macroevolutionary dynamics have led to a greater concentration of diversity of Hakea in the Mediterranean-climate-ecosystem of Southwest Australia compared to other biomes. Chapter Six narrows in on the Southwest biodiversity hotspot asking how pollination ecology in Hakea has evolved in response to high diversity of closely related species. Finally, I conclude by highlighting how the preceding chapters, which cover a broad range of topics, are intertwined in the aim of linking ecological and evolutionary processes to better understand spatial diversity patterns, all forming pieces of the same puzzle. I also briefly highlight future directions. Together, my thesis investigates the evolution of diversity using different approaches, united by the common goal of finding a better understanding of the patterns of diversity we appreciate in the world today.
... In areas protected from fire, such as narrow dune valleys with steep-sided walls, dune thicket reaches forest stature and includes several species that are rare in fire-exposed thicket for example Apodytes dimidiata (Icacinaceae), Chionathus foveolatus (Oleaceae), Zanthoxylum capense (Rutaceae) Van der Merwe, 1976). Thicket is dominated by tall (2-5 m), mesophyllous shrubs that form a dense, closed and often impenetrable shrubland (Vlok, Euston-Brown & Cowling, 2003) and is regarded as a fire-avoiding biome (Cowling et al., 2005;Linder, 2005). Fynbos, on the other hand, seldom exceeds 2 m in height and is a much more open community. ...
It has been hypothesised that high-intensity fires prevent fire-dependent fynbos from being replaced by fire-avoiding subtropical thicket on dune landscapes of the Cape Floristic Region (CFR). Recent extensive fires provided an opportunity to test this hypothesis. We posit that (1) fire-related thicket shrub mortality would be size dependent, with smaller individuals suffering higher mortality than larger ones; and (2) that survival and resprouting vigour of thicket shrubs would be negatively correlated with fire severity. We assessed survival and resprouting vigour post-fire in relation to fire severity and pre-fire shrub size at two dune landscapes in the CFR. Fire severity was scored at the base of the shrub and categorised into four levels. Pre-fire size was quantified as an index of lignotuber diameter and stem count of each shrub. Resprouting vigour consisted of two variables; resprouting shoot count and resprouting canopy volume. A total of 29 species were surveyed. Post-fire survival of thicket was high (83–85%). We found that smaller shrubs did have a lower probability of post-fire survival than larger individuals but could detect no consistent relationship between shrub mortality and fire severity. Fire severity had a positive effect on resprouting shoot count but a variable effect on resprouting volume. Pre-fire size was positively related to survival and both measures of resprouting vigour. We conclude that thicket is resilient to high-severity fires but may be vulnerable to frequent fires. Prescribed high-intensity fires in dune landscapes are unlikely to reduce the extent of thicket and promote fynbos expansion.
... Substantial intraspecific trait variation in many commonly measured leaf and stem structural traits has been observed in Protea species as well, and may reflect adaptation of ecotypes to the local environment (Carlson et al., 2011(Carlson et al., , 2016Prunier et al., 2012). Steep precipitation and temperature gradients in the CFR (Linder, 2005) may be strong selective factors on physiological traits related to the trade-off between carbon uptake and water conservation. ...
Background and aims:
Global plant trait datasets commonly identify trait relationships that are interpreted to reflect fundamental trade-offs associated with plant strategies, but often these trait relationships are not identified when evaluating them at smaller taxonomic and spatial scales. In this study we evaluate trait relationships measured on individual plants for five widespread Protea species in South Africa to determine whether broad scale patterns of structural trait (e.g. leaf area) and physiological trait (e.g. photosynthetic rates) relationships can be detected within natural populations, and if these traits are themselves related to plant fitness.
Methods:
We evaluated the variance structure (i.e. the proportional intraspecific trait variation relative to among species variation) for nine structural traits and the six physiological traits measured in wild populations. We used a multivariate path model to evaluate the relationships between structural traits and physiological traits, and the relationship between these traits and plant size and reproductive effort.
Key results:
While intraspecific trait variation is relatively low for structural traits, it accounts for between 50-100% of the variation in physiological traits. Further, we identified few trait associations between any one structural trait and physiological trait, but multivariate regressions reveal clear associations between combinations of structural traits and physiological performance (R2 of 0.37-0.64), and almost all traits had detectable associations with plant fitness.
Conclusions:
Intraspecific variation in structural traits leads to predictable differences in individual-level physiological performance in a multivariate framework, even though the relationship of any particular structural trait to physiological performance may be weak or undetectable. Furthermore, intraspecific variation in both structural and physiological traits leads to differences in plant size and fitness. These results demonstrate the importance of considering measurements of multivariate phenotypes on individual plants when evaluating trait relationships and how trait variation influences predictions of ecological and evolutionary outcomes.
... High species richness in some of these regions (e.g. the Andes [3][4][5], the succulent karoo [6], Qinghai-Tibetan plateau [7]) has been attributed to rapid radiation of multiple lineages coinciding with recent major geological and climatic events. In contrast, high species richness in other hotspots, such as the mediterranean climate regions of South Africa and southwestern Australia, have been attributed to a combination of recent radiations [8,9], lower extinction rates [10][11][12] and sustained accumulation of lineages over time [13][14][15]. The southwest Australian (SWA) hotspot has the lowest average net diversification rate and a disproportionate number of old lineages compared with other regions of high plant diversity [3,13]. ...
The diversification dynamics of the Australian temperate flora remains poorly understood. Here, we investigate whether differences in plant richness in the southwest Australian (SWA) biodiversity hotspot and southeast Australian (SEA) regions of the Australian continent can be attributed to higher net diversification, more time for species accumulation, or both. We assembled dated molecular phylogenies for the 21 most species-rich flowering plant families found across mesic temperate Australia, encompassing both SWA and SEA regions, and applied a series of diversification models to investigate responses across different groups and timescales. We show that the high richness in SWA can be attributed to a higher net rate of lineage diversification and more time for species accumulation. Different pulses of diversification were retrieved in each region. A decrease in diversification rate across major flowering plant lineages at the Eocene-Oligocene boundary (ca 34 Ma) was witnessed in SEA but not in SWA. Our study demonstrates the importance of historical diversification pulses and differential responses to global events as drivers of present-day diversity. More broadly, we show that diversity within the SWA biodiversity hotspot is not only the result of recent radiations, but also reflects older events over the history of this planet.
... The vegetation of these calcareous dunes consists of mosaics of fynbos (of Cape floristic affinity), thicket and forest (of subtropical affinity), the coexistence of which is thought to be governed by fire (Pierce & Cowling, 1991;Vlok et al., 2003). Dune thicket is dominated by tall, mesophyllous, shrubs (Midgley & Cowling, 1993) and is regarded to be fire avoiding and largely fire-free (Cowling et al., 2005;Linder, 2005). On the contrary, dune fynbos is a fire-prone and fire-dependent vegetation comprising fine-leaved, medium-sized sclerophyllous shrubs which are highly flammable (Van Wilgen et al., 1994;Kraaij & Van Wilgen, 2014). ...
Fire ecological research within the Cape Floristic Region is largely restricted to fynbos vegetation and, amongst fauna, birds. Nothing is known about post-fire responses of birds in subtropical thicket, which burns on much longer cycles than fynbos. Extensive fires in subtropical thicket along the southeastern Cape coast (in the Knysna area during June 2017) presented the opportunity to assess the response of these birds to fire. We predicted that (1) fire reduces bird species diversity, richness and abundance in thicket during the first two years post-fire; and (2) fire changes feeding guild composition and results in the loss of frugivorous birds. Bird surveys (point counts) were undertaken between 12-and 21-months post-fire in burnt (n =7) and unburnt (n = 7) thicket sites to determine bird community structure and abundance. A total of 66 bird species and 2404 individuals were recorded of which 52 species and 1176 individuals were recorded in burnt thicket and 60 species and 1228 individuals in unburnt thicket. Ten species occurred only in burnt thicket and 13 species only in unburnt thicket. There was a 21% loss of bird species (mainly forest birds) after fire. The Sørenson similarity coefficient was 60% for bird species composition between burnt and unburnt thicket. The most common feeding guilds in terms of richness and abundance in both burnt and unburnt thicket were insectivores and generalists. Frugivores were most abundant in unburnt thicket, whereas granivores were most abundant in burnt thicket. Changes in thicket bird community composition following the fire were minor and are likely to be short-lived as thicket shrubs re-sprout vigorously after fire resulting in rapid recovery of vegetation and thus bird habitat structure.
Biogeochemistry and biogeography are both vital, expanding, interconnected, hybrid, multidisciplinary, interdisciplinary, and transdisciplinary branches of the life, earth, and conservation sciences, with spatially and temporally oriented methodologies, and increasing relevance for current global realities and human survival. Both discipline clusters seek spatial relevance, from local to global scales, interconnectedness, linking multiple ecosystems, and use increasingly sophisticated research methodologies. Both may also use the tools of geomatics including geodesy, radio detection and ranging (radar), and light detection and ranging (LiDAR), to uncover more exact, reliable, and definitive information from researched data. For biogeochemistry, the main use for such techniques is the identification and measurement of the relevant parameters (organisms, habitat variables, earth structures that facilitate and contain chemical flows and reservoirs). For biogeography, spatial distributions assume prominence, including areal extents and differentiation. However, few studies have sought to document the increasingly complex relationship between these research clusters. This chapter uses a literature-based research methodology to uncover these issues, especially biogeography, as biogeochemistry has been defined in the earlier chapters. Selectivity is necessary, as this relationship is as broad as the Earth itself. Case studies are taken from the global scale of biomes and earth systems to the local contexts of ecological change. The role of human action is also explored, in addition to the possibilities of multidirectional change. Research methods within the field of geomatics, as the premier tools for the analysis of spatial ecologies and environmental variables, are also explored. It is argued that these three research clusters, when linked, form the basis of the environmental sciences. This contributes to the development of the environmental sciences and strengthens the status of biogeochemistry as a root science of the study of the Earth.
Southern Africa's Greater Cape Floristic Region (GCFR) – a hotspot of biological diversity and palaeo-anthropological evidence for modern human evolution – is a climatically complex region where broad climatic gradients influence the relative importance of plant photosynthetic types in local vegetation. This mix of photosynthetic pathways imprint an isotopic signature on palaeo-records, thereby allowing for the reconstruction of historical climate and vegetation. Here, we use vegetation plot data, coupled with the photosynthetic-type affinities of plant genera, to relate their relative cover to bioclimatic drivers and use these to create spatial distribution models of C3 and C4 grasses and CAM shrubs across the contemporary GCFR. We then use palae-odistribution modelling, drawing on downscaled climate models for the Last Glacial Maximum (LGM), to hindcast the LGM distributions of photosynthetic types for the GCFR and its then-exposed offshore areas. In addition, we construct a model to account for the effect of lower atmospheric CO2 concentration ([CO2]) during the LGM on the competitive interactions between C3 and C4 grasses and use this model to hindcast relative C4-grass cover across the glacial-era GCFR. Our palaeodistribution models suggest that, even though there were some reductions in CAM cover and shifts in C3-/C4-dominated grass layers between the LGM and Holocene, these were mostly localised, with changes at the regional scale being relatively muted. For C3/C4 grasses, distributional shifts were even more subtle once sub-ambient glacial [CO2] was accounted for. Our hindcasts of glacial, [CO2]-adjusted grass cover show agreements and inconsistencies with various sedimentary and herbivore-diet records in the palaeo-archive: both lines of evidence suggest the dominance of C3 species in the strongly winter-rainfall western GCFR; in the eastern GCFR, with muted rainfall seasonality, hindcasts of relative C3:C4 cover and δ13C signals from palaeo-records vary, with greater disparities between them. The lack of significant upheavals in the distribution of photosynthetic types suggests that the GCFR presented a relatively stable and dependable resourcescape for hunter-gatherer populations through the glacial-interglacial cycle of the LGM-Holocene transition. Our maps of relative C3-/C4-grass and CAM-shrub cover provide a reasonable surrogate for relative biomass of different photosynthetic types in local vegetation at a landscape scale and depict an independent estimate of carbon isoscapes across the GCFR-under both an interglacial (Holocene) and glacial (terminal Pleistocene) climate-against which palaeo-records can be assessed.
Ecological connectivity is the degree to which the landscape impedes or facilitates movement of organisms, i.e., genes, propagules, individuals, and populations, and combines both spatial and functional features. The human-dominated landscape with patched and isolated natural vegetation such as forests or grasslands should consider ecological connectivity. Buffer zones, corridors, and stepping stones are important components of ecological connectivity. Home gardens, farmland, Church forests, and roadsides need to be considered in ecological connectivity.KeywordsConnectivityNeophytesSacred forestsStepping stonesTree on farm
Background and aims – Numerous lineages in the Western Cape of South Africa show affinities with the floras of tropical Africa and Australasia. Isolepis subgenus Fluitantes, comprising seven to nine species, includes the broadly-defined I. fluitans, which occurs throughout Africa into Europe and Asia, as well as on both sides of the Indian Ocean. Thus, it is well suited for testing the generality of both the Cape-to-Cairo pattern of dispersal and transoceanic dispersal between southern Africa and Australasia.
Material and methods – We inferred a dated population-level phylogeny based on new sequence data from the nuclear ITS and the chloroplast atpI–H gene regions. We constructed dispersal–extinction–cladogenesis models in Lagrange to infer ancestral areas and to compare the likelihoods of stepping-stone and long-distance modes of dispersal.
Key results – The Fluitantes originated in the Cape about 7 million years ago (mya). They spread stepwise onto the mountains of East Africa and thence into Europe and the islands of the Indian Ocean, seemingly tracking their ancestral habitat. Australasia was colonised by a single long-distance dispersal event ca 3 mya. Incongruence between the plastid and nuclear gene trees was apparent for the Australasian taxa, I. crassiuscula, I. lenticularis, and I. producta, with their atpI–H sequences placing them with I. ludwigii in the Fluitantes and the ITS nrDNA resolving them in the Proliferae. Furthermore, two African taxa (I. graminoides, I. inyangensis) diagnosed on unique morphology are resolved as part of the widespread I. fluitans.
Conclusion – This study supports and extends the northward migration model that accounts for the Cape element of the Afromontane flora. Australasia was colonised directly from southern Africa, perhaps assisted by wind or waterfowl. Despite ancient hybridization associated with dispersal, we recognise the three taxa in Australasia as distinct, but synonymise I. graminoides and I. inyangensis into the widespread I. fluitans.
Background: Flowering plants (angiosperms) dominate most global ecosystems today, but their rapid Cretaceous diversification has remained poorly understood ever since Darwin referred to it as an ‘abominable mystery’. Although numerous Cretaceous fossil flowers have been discovered in recent years, most are represented by incomplete charcoalified fragments that do not preserve delicate structures such as complete petals and surface textures, which means that their similarity to living forms is often difficult to discern. The scarcity of information about the ecology of early angiosperms makes it difficult to test hypotheses about the drivers of their diversification. Among other factors, frequent fires in the Cretaceous have been postulated as having possibly facilitated the rise of angiosperms. However, to date no early fossil angiosperms displaying fire-adapted traits have been known, making the role of fire in shaping Cretaceous floras uncertain.
Results: We report the discovery of two exquisitely preserved fossil flower species, one identical to the inflorescences of the extant crown eudicot genus Phylica and the other recovered as a sister group to Phylica, both preserved as inclusions in Cretaceous amber from northern Myanmar (~99 Ma). These specialized flower structures, named Phylica piloburmensis sp. nov. and Eophylica priscastellata gen. et sp. nov., were adapted to surviving frequent wildfires, providing the earliest evidence of fire-resistance in angiosperms. The fossils suggest that fire was a significant selective force in Cretaceous angiosperm floras and that adaptations to fire resistance in some eudicot clades have been conserved for at least 99 Ma. This morphological stasis encompasses a range of floral characters, including the production of ‘pseudo-flowers’, and characteristic fruit and pollen architecture. Given its morphological distinctiveness, the Eophylica-Phylica clade represents one of the first well-documented angiosperm ‘living fossil’ genera from the Cretaceous.
Conclusion: Our study suggests that core eudicots with specialised flower morphology displaying hallmarks of fire resistance and identical to those of the extant south African genus Phylica, had originated by the mid-Cretaceous (~99 Ma). Palaeoenvironmental reconstructions indicate that these plants lived in conditions similar to those of present-day southern Africa where 70% of taxa survive frequent burning, and that fire resistance was probably widespread in the fire-prone Cretaceous. The results also provide new insights into the biogeographic origin of at least one element of the highly endemic Greater Cape Region biodiversity hotspot flora biota.
With extraordinary levels of plant diversity and endemism, the Brazilian campos rupestres across the Espinhaço Range have a species/area ratio 40 times higher than the lowland Amazon. Although diversification drivers in campos rupestres remain a matter of debate, the Pleistocene refugium hypothesis (PRH) is often adopted as the most plausible explanation for their high diversity. The PRH has two main postulates: highland interglacial refugia and a species pump mechanism catalysed by climatic changes. We critically assessed studies on campos rupestres diversification at different evolutionary levels and conclude that most of them are affected by sampling biases, unrealistic assumptions or inaccurate results that do not support the PRH. By modelling the palaeo-range of campos rupestres based on the distribution of 1123 species of vascular plants endemic to the Espinhaço Range and using climate and edaphic variables, we projected a virtually constant suitable area for campos rupestres across the last glacial cycle. We challenge the great importance placed on Pleistocene climatic oscillations in campos rupestres plant diversification and offer an alternative explanation named escape-to-radiate model, which emphasizes niche shifts. Under this biogeographic model of diversification, the long-term fragmentation of campos rupestres combined with recurrent extinctions after genetic drift and sporadic events of adaptive radiation may provide an explanation for the current diversity and endemism in the Espinhaço Range. We conclude that long-term diversification dynamics in campos rupestres are mainly driven by selection, while most endemic diversity is ephemeral, extremely fragile and mainly driven by drift.
Aizoaceae are one of the most diverse succulent plant families in the world, with c. 2 400 species, and they are a major component of the Greater Cape Floristic Region of South Africa. Despite this diversity, genome size (GS) has only been recorded in three of the c. 144 genera of Aizoaceae. This study provides the first comprehensive assessment of GS in the family with 109 genera measured (76% of genera). GS (2C) is conserved in Aizoaceae, varying from 0.54 to 6.34 pg (0.53–6.20 Gbp), with a mean of 2.6 pg. No significant differences between GS and the ecological and environmental traits tested were recovered. Infrageneric GS was explored in the most diverse stoneplant genus, Conophytum, and was found to be extremely conserved [0.98–2.24 pg (1C)]. Furthermore, the extent of endoreduplication in Conophytum was determined across 46 species. Leaf and flower tissues of Conophytum are highly polysomatic and ploidy states of 2C–64C were typically observed across the genus, with some instances of 128C. The relatively conserved and small GS measured across Aizoaceae and in Conophytum is possibly linked to the recent and rapid radiation of the family.
In this chapter, sclerophyllous forests and shrublands are discussed; in contrast to the subtropics with year-round rain, they are located on the western sides of the continents, where precipitation occurs mainly in winter. Hot and dry summers promote trees with a low transpiration rate, particularly in areas with nutrient-poor soils. The five winter rainfall areas (Mediterranean region, California, central Chile, southern Africa, southwestern Australia) differ distinctly with regard to their floristic species pool. They are all species-rich and contain many specialists that are able to cope with aridity during the thermally favorable summer. Fire is a factor that shapes the vegetation in California, South Africa and Australia. The Mediterranean region has a cultural history stretching back thousands of years, which makes it highly difficult to reconstruct the natural vegetation.
Patch size (area) and isolation (inverse distance to source) are key variables of island biogeography, but their application in conservation planning has recently come under scrutiny. Based on animal distribution data in fragmented landscapes from around the world it was postulated that occupancy was poorly predicted by patch size and isolation. Do these findings also apply to arid areas and to plants?
This question was investigated in four inselberg landscapes in the Namib Desert stretching over a 770 km climatic north–south gradient. Inselbergs (isolated mountains) are special habitats and can be considered ‘islands’ of more mesic conditions in an arid matrix. Species richness of inselberg specialists was used as an indicator and regressed against area, distance to nearest habitat and distance to ‘mainland’ (or source pool, which are proxies for level of isolation). Additionally, the influence of landscape geographic position, land use and rock types were studied. Responses of different life forms and individual plant species as well as possible dispersal limitations were also investigated.
Whether patch size is more important than isolation in determining species richness on arid inselbergs could not be answered at a landscape level. However, when investigated on a functional and species level, isolation was of greater importance than patch size for trees and also for selected species such as Commiphora saxicola and Heliotropium steudneri. The effect of distance to source in this study is likely a function of spatial distance as well as a coast-inland moisture gradient. Inselberg specialist-richness was not affected by land use or the bioclimatic position. Yet rock type, which is a reflection of soil physical and chemical properties did affect species richness with granites and basalts supporting more species. Life forms of inselberg specialists were influenced by the investigated environmental variables, but dispersal limitations were not. Despite inconclusive results at a landscape level, functional groups and individual species provided more conclusive results. This points towards the necessity of additional investigations at a finer scale to gain an understanding of the factors driving species distributions. In future more detail regarding the ‘matrix’ surrounding ‘patches’, as well as evolutionary and vegetation historic factors should be explored. Phylogenetic studies would be one tool to help unravelling some of the presently unknown factors affecting species distributions on Namib inselbergs. This study also highlighted the importance of inselbergs in arid landscapes as ‘hotspots’ of species richness and species of conservation importance.
The wide variation of diaspore types in African Restionaceae reflects two different evolutionary strategies for utilisation of resources for reproduction and propagation. The interplay between fecundity and seedling survivorship has apparently resulted in reproductive strategies ranging from the production of a few large dispersal units with comparatively high drought resistance, to production of numerous, smaller dispersal units which experience high levels of drought mortality. A sample of Restionaceae representing all the major African lineages in the family was examined to investigate the influence of diaspore size on diaspore production, seedling growth and seedling survival in the fynbos vegetation of the Western Cape. Correlates of diaspore size were investigated by using phylogenetically independent contrasts to assess which ecological factors may have influenced the evolution of different dispersal mechanisms. Results indicate that diaspore size strongly influences the size to which a seedling can grow in its first few months, which in turn influences the plant's ability to survive summer drought. Larger seedlings, produced by larger diaspores, are less likely to succumb to drought-induced mortality than the smaller seedlings produced by smaller diaspores. The evolution of large, drought-resistant diaspores coincides with a hypothesised drying of the Western Cape climate between 5 and 7 million years ago. This occurrence of seasonal drought may have opened up a new ecological opportunity for plants producing drought-resistant propagules, which, under wetter conditions, would be overwhelmed by less robust seedlings through sheer weight of numbers produced.
The heathy, sclerophyllous vegetation type known locally in South Africa as 'fynbos' is not restricted to the Cape Floral Kingdom (CFK), but occurs throughout sub-Saharan Africa, Madagascar and the Mascarene Islands. The fynbos shrublands of these regions occur mostly in cool, montane environments where rainfall is high and soils are highly leached. Montane environments, however, are not the sole repositories of fynbos-type communities. Outcrops of Msikaba Formation (Pondoland) Sandstone in KwaZulu-Natal, South Africa, support similar shrublands, including many 'typical' fynbos genera and growth forms, The floristic and physiognomic resemblance of communities to the CFK, especially fragments of the high-altitude eastern (Afromontane) corridor extending into tropical East Africa, has prompted much speculation. A preliminary phytogeographical account is presented concerning the distribution of fynbos ('Cape') elements in the Drakensberg Alpine Region (DAR) and Pondoland Sandstone Region: two biotopes in southern Africa which share Cape elements. The significant sharing of Cape elements between biotopes suggests analogous growth environments.
Historical biogeographic patterns of relationships among southern and northern South America, North America, and southern temperate areas were investigated by a cladistic biogeographic analysis of 17 taxon cladograms. Three techniques were applied: Wiley's biogeographic parsimony analysis, Nelson and Platnick's component analysis, and Humphries, Ladiges, Roos, and Zandee's quantification of component analysis. Biogeographic parsimony analysis yielded two general area cladograms (CI = 0.74). Under component analysis, six general area cladograms (two under Nelson and Platnick's assumption 1 and four under their assumption 2) were obtained through the intersection of a maximum of 10 sets of area cladograms. Quantification of component analysis produced nine cladograms (CI = 0.50) under assumption 1 and one (CI = 0.45) under assumption 2. The results support a hybrid origin of the South American biota. The northern South American biota is most closely related to that of North America, and southern South America constitutes a monophyletic group together with Australia, Tasmania, New Guinea, New Caledonia, and New Zealand, reflecting the existence of an ancient austral biota. Four conflicting hypotheses of area relationships concerning southern South America and the other austral areas are proposed, suggesting that southern South America may be a composite area in itself.
It is often claimed that we do not understand the forces driving the global diversity gradient. However, an extensive literature suggests that contemporary climate constrains terrestrial taxonomic richness over broad geographic extents. Here, we review the empirical literature to examine the nature and form of the relationship between climate and richness. Our goals were to document the support for the climatically based energy hypothesis, and within the constraints imposed by correlative analyses, to evaluate two versions of the hypothesis: the productivity and ambient energy hypotheses. Focusing on studies extending over 800 km, we found that measures of energy, water, or water-energy balance explain spatial variation in richness better than other climatic and non-climatic variables in 82 of 85 cases. Even when considered individually and in isolation, water/ energy variables explain on average over 60% of the variation in the richness of a wide range of plant and animal groups. Further, water variables usually represent the strongest predictors in the tropics, subtropics, and warm temperate zones, whereas energy variables (for animals) or water-energy variables (for plants) dominate in high latitudes. We conclude that the interaction between water and energy, either directly or indirectly (via plant pro- ductivity), provides a strong explanation for globally extensive plant and animal diversity gradients, but for animals there also is a latitudinal shift in the relative importance of ambient energy vs. water moving from the poles to the equator. Although contemporary climate is not the only factor influencing species richness and may not explain the diversity pattern for all taxonomic groups, it is clear that understanding water-energy dynamics is critical to future biodiversity research. Analyses that do not include water-energy variables are missing a key component for explaining broad-scale patterns of diversity.
Taxa have been dated using three methods: equating their age with the age of the oldest known fossil, with the age of strata the taxa are endemic to, and with the age of paleogeographic events. All three methods have been adopted as methods of dating nodes in molecular phylogenies. The first method has been the most popular, but both this and the second method involve serious difficulties. Studies often, correctly, introduce oldest known fossils as providing minimum ages for divergences. However, in the actual analyses these ages, and ages derived from them, are often treated as absolute ages and earlier geological events are deemed irrelevant to the phylogeny. In fact, only younger geological events can be irrelevant. Studies correlating the age of nodes with age of volcanic islands often overlook the fact that these islands have been produced at subduction zones or hot spots where small, individually ephemeral islands are constantly being produced and disappearing, and a metapopulation can survive indefinitely. Correlating the age of taxa with that of associated paleogeographic events is probably the most promising method but has often been used in a simplistic way, for example in assuming that all divergence across the Isthmus of Panama dates to its final rise. Most workers now agree that a global molecular clock does not exist, and that rates can change between lineages and within a lineage over time. New methods of estimating branch lengths do not assume a strict clock, but the number of models for molecular evolution is then effectively infinite. Problems with calibrating the nodes, as well as with substitution models, mean that phylogeography's claim to be able to test between vicariance and dispersal is not justified.
© The Willi Hennig Society 2005.
The studies presented in this paper analyse diversity patterns of land plants (mosses, ferns, gymnosperms, and angiosperms) at continental to global scales. A revised version of our earlier world map of vascular plant species richness and the first maps of species richness of mosses and gymnosperms on a global scale are presented. Diversity patterns of vascular plants are correlated with different measures of geodiversity (the diversity of the abiotic environment). Global centres of vascular plant diversity coincide with highly structured, geodiverse areas in the tropics and subtropics. These are the Chocó-Costa Rica region, the tropical eastern Andes and the north western Amazonia, the eastern Brazil, the northern Borneo, and New Guinea, as well as the South African Cape region, southern Mexico, East Himalaya, western Sumatra, Malaysia, and eastern Madagascar. Constraints imposed by the physical environment, such as the length of the thermal vegetation period or water availability, shape large scale trends of biodiversity. However, important centres of species richness and endemism can only be explained when taking into account the history of the floras. The main diversity centres in SE Asia are the same for gymnosperms as for all other vascular plants, but in other parts of the tropics and subtropics there is low gymnosperm diversity. The exceptions to this pattern are Mexico and California, which have almost as many species of gymnosperms as SE Asia. The increase in the number of species and genera published during the last 250 years is documented, based on data from the Index Kewensis. The first continental maps of Cactaceae diversity at species and genus level are used to show how choice of the taxonomic level affects the analysis and its implications for priority setting in biodiversity conservation. In this context, global biodiversity hotspots are discussed and an alternative world map of hotspots is proposed.
The high plant diversity of mediterranean-climate regions has attracted much attention over the past few years. This review discusses patterns and determinants of local, differential and regional plant diversity in all five regions. Local diversity shows great variation within and between regions and explanations for these patterns invoke a wide range of hypotheses. Patterns of regional diversity are the result of differential speciation and extinction rates during the Quaternary. These rates have been influenced more by the incidence of fire and the severity of climate change than by environmental heterogeneity. All regions have a high number of rare and locally endemic taxa that survive as small populations, many of which are threatened by habitat transformation.
Heliophila (ca. 73 spp.), the ditypic Cycloptychis and Thlaspeocarpa, and the monotypic Schlechteria, Silicularia, Brachycarpaea, and Chamira are endemic to the Cape region of South Africa, where they are the dominant genera of Brassicaceae. They may be regarded as the most diversified Brassicaceae lineage in every aspect of habit, leaf, flower, and fruit morphology. The characters used in the separation of these genera and their species, especially fruit type (silique vs. silicle), dehiscence (dehiscent vs. indehiscent), compression (latiseptate vs. angustiseptate), and cotyledonary type (spirolobal, diplecolobal, twice conduplicate), have been used extensively in the delimitation of tribes. The relationship and taxonomic limits among these genera are unclear and controversial. The present ITS study demonstrates the monophyly of tribe Heliophileae, with Chamira as sister clade. The other five smaller genera above are nested within two of the three main lineages of Heliophila, to which they should be reduced to synonymy. The current study reveals parallel evolution of fruit characters often used heavily in the traditional classification schemes of the family. However, the arrangement of species into three main clades largely corresponds with the distribution of morphological characters (e.g., habit, leaf shape, seed structure, inflorescence type, and presence/absence of basal appendages on the pedicels, petals, and staminal filaments) not adequately accounted for in previous studies. Estimation of divergence times of the main lineages of Heliophila is in agreement with recent estimations in other plant groups, all of which date the diversification against a background of aridification in the Pliocene and Pleistocene. Species of one main clade are perennial, microphyllous shrubs/subshrubs typically restricted to poor sandstone soils in the southwestern and western parts of the Cape Floristic Region of South Africa. Species of the other two clades are predominantly annuals that grow in more arid regions of Namibia and Namaqualand, as well as in the above sandstone areas of the Cape Region. The adaptive significance of various floral structures is discussed in terms of their possible role in the rapid diversification within Heliophila.
A deep-sea sediment core underlying the Benguela upwelling system off southwest Africa provides a continuous time series of sea surface temperature (SST) for the past 4.5 million years. Our results indicate that temperatures in the region have declined by about 10 degrees C since 3.2 million years ago. Records of paleoproductivity suggest that this cooling was associated with an increase in wind-driven upwelling tied to a shift from relatively stable global warmth during the mid-Pliocene to the high-amplitude glacial-interglacial cycles of the late Quaternary. These observations imply that Atlantic Ocean surface water circulation was radically different during the mid-Pliocene.
Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which
are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming
and cooling driven by tectonic processes on time scales of 105to 107 years, rhythmic or periodic cycles driven by orbital processes with 104- to 106-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 103 to 105 years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily
on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation
of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen
mechanisms for altering climate.
I propose that global patterns in numbers of range-restricted endemic species are caused by variation in the amplitude of climatic change occurring on time-scales of 10-100 thousand years (Milankovitch oscillations). The smaller the climatic shifts, the more probable it is that palaeoendemics survive and that diverging gene pools persist without going extinct or merging, favouring the evolution of neoendemics. Using the change in mean annual temperature since the last glacial maximum, estimated from global circulation models, I show that the higher the temperature change in an area, the fewer endemic species of mammals, birds, reptiles, amphibians and vascular plants it harbours. This relationship was robust to variation in area (for areas greater than 10(4) km2), latitudinal position, extent of former glaciation and whether or not areas are oceanic islands. Past climatic change was a better predictor of endemism than annual temperature range in all phylads except amphibians, suggesting that Rapoport's rule (i.e. species range sizes increase with latitude) is best explained by the increase in the amplitude of climatic oscillations towards the poles. Globally, endemic-rich areas are predicted to warm less in response to greenhouse-gas emissions, but the predicted warming would cause many habitats to disappear regionally, leading to species extinctions.
Climatic and geological change may play a key role in stimulating biological radiations. Here, we use phylogenetic data to test whether the comparatively high diversity of ehrharteoid grasses in the Cape region of South Africa is the result of rapid radiation associated with the onset of a seasonally arid climate during the late Miocene. A phylogenetic hypothesis based on morphological and nucleotide sequence (nuclear ITS1 and plastid trnL-F) data confirms the monophyly of the African Ehrharta species and shows that the diversification of this lineage was centered in the Cape region. Sequence divergence data (ITS1 + trnL-F) indicate a pulse of rapid speciation, which may explain poor phylogenetic resolution within the African Ehrharta clade. Alternative calibrations yield a broad range of time estimates for the start and end of this radiation, most of which indicate a radiation inside the last 11 million years. A calibration based on the age of Ehrhartoideae suggests that radiation started 9.82 +/- 0.20 million years ago and ended 8.74 +/- 0.21 million years ago. Under alternative calibrations, estimated speciation rates during the period of radiation range between 0.87 and 4.18 species per million years. Parsimony optimization of habitat parameters reveals that radiation was correlated with the occupation of seasonally arid succulent karoo environments, wet heathy (fynbos) environments being ancestral. These data support earlier suggestions that late Miocene climatic change stimulated floristic radiation at the Cape, and highlight the potential importance of environmental change in powering diversification in continental floras.
The Succulent Karoo is an arid region, situated along the west coast of southern Africa. Floristically this region is part of the Greater Cape Flora and is considered one of the Earth's 25 biodiversity hotspots. Of about 5,000 species occurring in this region, more than 40% are endemic. Aizoaceae (ice plants) dominate the Succulent Karoo both in terms of species numbers (1,750 species in 127 genera) and density of coverage. Here we show that a well-supported clade within the Aizoaceae, representing 1,563 species almost exclusively endemic to southern Africa, has diversified very recently and very rapidly. The estimated age for this radiation lies between 3.8 and 8.7 million years (Myr) ago, yielding a per-lineage diversification rate of 0.77-1.75 per million years. Both the number of species involved and the tempo of evolution far surpass those of any previously postulated continental or island plant radiation. Diversification of the group is closely associated with the origin of several morphological features and one anatomical feature. Because species-poor clades lacking these features occur over a very similar distribution area, we propose that these characteristics are key innovations that facilitated this radiation.
Angiosperms are among the major terrestrial radiations of life and a model group for studying patterns and processes of diversification. As a tool for future comparative studies, we compiled a supertree of angiosperm families from published phylogenetic studies. Sequence data from the plastid rbcL gene were used to estimate relative timing of branching events, calibrated by using robust fossil dates. The frequency of shifts in diversification rate is largely constant among time windows but with an apparent increase in diversification rates within the more recent time frames. Analyses of species numbers among families revealed that diversification rate is a labile attribute of lineages at all levels of the tree. An examination of the top 10 major shifts in diversification rates indicates they cannot easily be attributed to the action of a few key innovations but instead are consistent with a more complex process of diversification, reflecting the interactive effects of biological traits and the environment.
Data assembled from recent publications on plant-pollinator systems in southern African plants reveal a pattern of remarkable specialization by the plants. Analysis of plant species in two large families - the Orchidaceae and Iridaceae - showed that most have been found to be pollinated by a single animal species. Similar levels of specialization are evident in southern African plants pollinated by oil-collecting bees, long-proboscid flies, butterflies and hopliine beetles. By contrast, analysis of published data for the Orchidaceae and Polemoniaceae in the northern hemisphere showed that most species have relatively generalized pollination systems (median number of pollinator species = 3.5 and 5, respectively). Claims made in the literature that generalization is the rule rather than the exception in plant pollination systems have been based solely on studies in cool temperate ecosystems in the northern hemisphere and may be premature if there are strong regional differences in the degree of specialization in plants. This highlights the need for more studies of pollination systems across a range of ecosystems and geographical regions in orderto obtain an accurate global view of the diversity of plant pollination systems.
The study of rates of character evolution has been a cornerstone of evolutionary biology since the pioneering work of Simpson (1944). It has occupied a similar position in molecular evolutionary studies since Zuckerkandl and Pauling’s (1962, 1965) proposal of the molecular clock. There is a fascinating contrast between these two works, however. Simpson used information about time, from the fossil record, to draw inferences about rates and modes of evolution. His main conclusion was that such rates are highly variable. Although also using information from fossils, Zuckerkandl and Pauling came to just the opposite conclusion about rates of protein evolution. They then argued that if proteins evolved at a roughly constant rate, a study of rates and modes of evolution could be used to say something about timing of events in evolutionary history. Both these ideas about the tempo of character evolution have achieved nearly the status of null hypotheses in their respective disciplines. Although Simpson clearly inferred that some morphological rates have been nearly linear, or “clock-like” over at least moderate periods of time (e.g., Simpson, 1944, pp. 203-204), few paleontologists or morphologists give credence to the notion of morphological clocks. And although there is indisputable evidence that many genes and proteins do not evolve at a constant rate through time (Britten, 1986; Avise, 1994), molecular rate constancy continues to be viewed as a reasonable model even across vast reaches of the tree of life (Wray et al., 1996).
Johnson, S. D.: Pollination, adaptation and speciation models in the Cape flora of South Africa. – Taxon 45: 59‐66. 1996. – ISSN 0040‐0262.
Recent species definitions have placed emphasis on “diagnostic characters” rather than isolating mechanisms. Such characters can be informative about the evolutionary processes which lead to speciation in highly diversified plant groups, such as those found in the Cape floral region of South Africa. Rampant speciation in the Cape flora has often been attributed to heterogeneity of the physical environment, yet many large Cape genera show radiation in floral, rather than vegetative, characters, which suggests that adaptation to pollinators has played a major role in speciation. Selection for more efficient pollination systems in a pollinator‐limited context, rather than isolating mechanisms, is suggested to be the primary driving force behind floral evolution in the Cape flora.
ABSTRACT Comprising a land area of ca. 90,000 km,, less than one twentieth (5%) the land area of the southern African subcontinent, the Cape Floristic Region (CFR) is, for its size, one of the world’s richest areas of plant species diversity. A new synoptic flora for the Region has made possible an accurate reassessment of the flora, which has an estimated 9030 vascular plant species (68.7% endemic), of which 8920 species are flowering plants (69.5% endemic). The number of species packed,into so small an area is remarkable,for the temperate,zone and compares,favorably with species richness for areas of similar size in the wet tropics. The Cape region consists of a mosaic,of sandstone,and shale substrata with local areas of limestone. It has a highly dissected, rugged topography, and a diversity of climates with rainfall mostly falling in the winter months and varying from 2000 mm,locally to less than 100 mm. Ecological gradients are steep as a result of abrupt differences in soil, altitude, aspect, and precipitation. These factors combine to form an unusually large number of local habitats for plants. Sandstone-derived soils have characteristically low nutrient status, and many plants present on such soils have low seed dispersal capabilities, a factor promoting localized distributions. An unusual family composition includes Iridaceae, Aizoaceae, Ericaceae, Scrophulariaceae, Proteaceae, Restionaceae, Rutaceae, and Orchidaceae among the 10 largest families in the flora, following Asteraceae and Fabaceae, as the most speciose families. Disproportionate radiation has resulted in over 59.2% species falling in the 10 largest families and 77.4% in the largest 20 families. Twelve genera have more than 100 species and the 20 largest genera contribute some 31% of the total species. Species richness of the Cape flora is hypothesized to be the result of geographic and parapatric radiation in an area with a mosaic of different habitats due to local soil, climate, and altitudinal differences that combine,to produce steep ecological gradients. Also contributing to the diversity has been a relatively stable geological history since the end of the Miocene that saw the establishment,of a semi-arid and extreme seasonal climate at the southwestern,part of southern Africa. Key words: floristics, Mediterranean-type climate, phytogeography, plant diversity, southern Africa, speciation. Situated at the southwestern tip of the African
The leaf-anatomy, palynology, seed-morphology, vegetative morphology and especially the highly complicated floral morphology of theCoryciinae s. str. (Diseae: Orchidoideae: Orchidaceae) are described and illustrated in detail. On the basis of these characters the presumed phylogeny, based on a rigorous cladistic analysis, is presented. The cladistic biogeographical analysis of theCoryciinae s. str. shows that it is a member of the Afrotemperate Track, with a pattern of vicariance events typical of the members of this track. An analysis of the patterns of speciation shows that allopatric speciation appears to be rare, and that parapatric speciation across edaphic boundaries may be the most important factor. Proceeding from the information presented, a new classification of the group is proposed in which we recognize the four generaCeratandra, Evotella, Pterygodium andCorycium. The new monotypic genusEvotella comprises a species originally described asPterygodium rubiginosum. The three species of the genusAnochilus are transferred toCorycium andPterygodium. P. magnum, which was originally described asPterygodium but was transferred toCorycium lately, is placed in a monotypic section ofPterygodium.
Pollination strategies adopted by the largely sub-Saharan African Gladiolus (approximately 260 species), one of the largest genera of the monocot family Iridaceae, are unusually diverse. The primary or sole pollinators include long-tongued apid and amhophorine bees (Apidae), short-tongued halictid and andrenid bees (Halictidae, Andrenidae), sometimes in combination with hopliine beetles (Scarabaeidae), long-prohoseid flies (Nemestrinidae, Tabanidae), large butterflies (Satyridae), moths (mostly Noctuidae and Sphingidae), and sunbirds (Passerinae.). Floral form correlates closely with pollination strategy, allowing us to infer the pollination ecology of almost all 165 species in southern Africa, although we have observations of animal visitors capable of accomplishing pollen transfer in only half this number. Pollination by apid bees foraging for nectar and passively transferring pollen brushed onto their bodies during feeding occurs in all seven sections of the genus in southern Africa and is also the most common strategy in five of these sections. Other pollinators include female bees actively foraging for pollen, or long-proboseid flies, sunbirds, moths, the satyrid butterfly, Aeropetes, all foraging for nectar, and in one species hopliine beetles that use the flowers as sites for assembly and copulation. Shifts in floral form associated with changes in pollination appear complex in the large flowers of Gladiolus species, but may in fact involve relatively simple developmental modifications, involving changes in perianth pigmentation, and often the type of marking on the tepals, presence or absence of scent, length of the perianth tube, and occasionally a shift from zygomorphy to actinomorphy. Associated with these changes is a correlated adjustment in nectar characteristics, including volume, sugar concentration, and sometimes sugar chemistry. With an inferred minimum of 32 shifts in pollination system in the 165 species in southern Africa, Gladiolus appears to have an unusually labile floral morphology, which may account for its extensive adaptive. radiation.
Some 14 species of long-proboscid flies (Diptera) in two families, Nemestrinidae and Tabanidae, with elongated mouth parts are known to pollinate species in several plant families, most importantly Geraniaceae, Iridaceae, and Orchidaceae, across southern Africa. Long-proboscid fly pollination appears to comprise three discrete guilds of flies in the genera Prosoeca, Moegistorhynchus, and Stenobasipteron (Nemestrinidae) and Philoliche (Tabanidue). Flies in the three guilds are on the wing at different times of the year and pollinate different suites of plant species, sometimes with different floral characteristics. The three pollinator guilds operate for the most part in different parts of the subcontinent. Where there is geographical overlap, the periods of activity differ. Plants pollinated by long-proboscid flies have flowers with an elongate, cylindrical floral tube, mostly 35-60 cm long, a perianth of specific colors and marking, a floral reward of nectar, and lack floral fragrance. Pollen is not eaten by these flies, and anthers and pollen are often cryptically colored. Flowers are usually zygomorphic and bilabiate, and the petal or tepal lobes have characteristically shaped nectar guides. With few exceptions, the flowers offer ample nectar of sugar concentration mainly in the 20-30% range. Several orchids and one Pelargonium using long-proloscid flies for pollination offer no nectar, and pollination is accomplished through floral mimicry and deception. In long-proboscid fly pollination systems, plasement of pollen on the insect's body is highly specific, and there are at least six mutually exclusive sites of pollen deposition on an insect's body. When two or more long-proboscid-fly-pollinated plant species co-occur, each typically utilizes a different pollen deposition site. This suggests that pollen contamination is detrimental to reproductive success and that differential pollen deposition sites are important for plants pollinated by long-proboscid flies. Since these flies are the sole or main pollinators of at least 120 plant species and the inferred pollinators of at least 80 more species in southern Africa, they must be considered keystone species in the ecosystems where they occur.
To test the molecular dating results and biogeographic in-terpretations reported by Conti et al. (2002), R. G. Moyle reanalyzed our published dataset of 13 rbcL sequences rep-resenting Melastomataceae and five small taxa: the Southeast Asian Crypteroniaceae (the C clade) and their western Gond-wanan sister clade, formed by the South American Alzatea and the African Rhynchocalyx, Oliniaceae, and Penaeaceae (the AROP clade). Using a single calibration point and non-parametric rate smoothing (NPRS; Sanderson 2003), Moyle (2004) estimated an age of 68 million years ago (mya; 10.6 mya) for the split between Crypteroniaceae and the AROP clade, which contrasts with our published age of 116 mya (24 mya), obtained with fossil calibration and pe-nalized likelihood (PL; Sanderson 2003), and an age range of 50 to 151 mya, obtained by using three different calibration points and three different dating methods. Moyle (2004) con-cludes that his estimated age for the origin of the Crypter-oniaceae stem lineage is ''not congruent with a strict Gond-wanan vicariance hypothesis for the distribution of Crypter-oniaceae and nearest relatives'' and that the differences in calibration ''explain most of the differences in results.'' Although Moyle's comment is timely by focusing on one of the most problematic issues in molecular dating analyses— namely, calibration—we would like to highlight some weak-nesses in his chosen analytical procedure, along with factual inaccuracies and misrepresentations of our original article. At the same time, we offer some general reflections on the controversial issue of calibration in molecular dating anal-yses. The criticism posed by Moyle that is most readily ad-dressed concerns the phylogenetic placement of the South American Alzatea. Moyle's (2004) maximum likelihood (ML) analyses supported the placement of the South Amer-ican Alzatea within the African clade, rather than as sister to the African clade as reported in Conti et al. (2002). He pro-posed that this discrepancy may be explained by the use of different models of nucleotide substitution in the two anal-yses, adding that low statistical support for the position of Alzatea suggests that its relationships remain unresolved. However, we would like to note that Moyle used outgroups (Hauya, Onagraceae and Quisqualis, Combretaceae) that are phylogenetically more distant from the CAROP/Melasto-mataceae clade than the outgroup we used (Heteropyxis, rep-resenting the sister clade of the CAROP/Melastomataceae clade; see Conti et al. 1996). After rerunning ML analyses with different combinations of outgroups and substitution models, we have concluded that instability in the position of Alzatea is caused primarily by different outgroup choices. A second point of disagreement concerns the properties and inferential value of the estimated age ranges. Moyle (2004) states: ''Because of the wide range of age estimates produced by the different calibration points and molecular dating procedures, I re-examined the biogeographic history of Crypteroniaceae with particular attention to calibration procedure.'' He then elaborates on results based on a single dating method (NPRS) and a single calibration point (an age of 23 mya assigned to node E). This methodological approach will tend to provide a narrower range of estimated ages than would be obtained by using a number of different methods, but such a superficially precise result may not be indicative of increased accuracy. Indeed, from a strictly analytical per-spective, the choice of NPRS as the single dating method is questionable, since NPRS tends to overfit the data, especially when rates of molecular evolution change abruptly (Sander-son 2002). A more critical issue, however, is the way in which fossils are used to calibrate trees. Moyle used a single calibration point based on seeds that are dated at 23–26 mya and char-acterized by the large testa tubercles arranged in rows. These seeds have been assigned confidently to Melastomeae, which were monophyletic in recent analyses (Renner et al. 2001; Renner and Meyer 2001; see also Collinson and Pingen 1992). Yet, most likely due to scarce sampling, the three representatives of Melastomeae (Tibouchina, Osbeckia, and Rhexia) included in our rbcL analysis did not form a mono-phyletic group, but were members of a clade that also in-cluded Medinilla from the Dissochaeteae/Sonerileae (Conti et al. 2002, fig. 3). It was for this reason that we refrained from using this fossil as a calibration point. Moyle (see his fig. 1), in contrast, used the age of 23 mya to constrain node E, which subtends a clade formed by members of Melasto-meae and Dissochaeteae/Sonerileae. Since node E necessarily predates the origin of the Melastomeae, to which the fossil seeds may be assigned (see also Renner et al. 2001, fig. 1; Renner and Meyer 2001, fig. 3), Moyle's improper calibration procedure automatically produces an underestimation of all nodal ages. A further source of disagreement between Moyle's and our analyses concerns the nodal assignment of fossil leaves (dat-ed at 53 mya) that are characterized by acrodromous venation, a synapomorphy exclusive for Melastomataceae among the sampled taxa (Renner et al. 2001). Moyle criticizes our de-cision to use these fossil leaves to constrain the base of the Melastomataceae crown group (corresponding to node E in his fig. 1), instead of the base of its stem lineage (corre-sponding to node D in his fig. 1). Although we agree with
Aim
To evaluate competing views on the origin and distribution of the New Zealand flora by testing the hypothesis that the geographical distribution of species is unrelated to ecological traits such as habitat requirements and dispersal capabilities.
Location
The New Zealand archipelago.
Methods
An analysis of the factors correlated with distribution and endemism for alpine plants within New Zealand, and for the New Zealand biota as a whole.
Results
Woody plants are highly endemic; nonendemic plants tend to be herbaceous and are concentrated among the highly dispersible ferns and fern allies, orchids and wetland plants. These groups make up 32% of the total flora but contribute 78% of nonendemics. Alpine plants with wide spatial distribution tend to have greater altitudinal ranges, a broader habitat preference and better dispersal ability.
Main conclusions
Most vascular plants reached New Zealand by long‐distance transoceanic dispersal, probably during the Late Miocene to early Pleistocene period. During the Miocene and Pliocene, similar climates and landscapes to those of Australia and northern island groups, and highly invasible terrain, permitted dispersal of woody plants. Cooling climates and formation of a more mountainous, more compact landscape after that time reduced dispersal of woody plants and favoured herbaceous, wetland and highly dispersible plant groups. The prominence of dispersal has led to intense selective immigration, and is responsible for many characteristic features of the flora. Species selection by glacial–interglacial cycles has restricted acquisition or retention of cool or arid climate adaptations, particularly in the lowland flora. Endemic and range disjunction patterns in the New Zealand mainland are not, in general, directly caused by Pliocene inundations or the faulting and associated horizontal displacement of terrain that has continued since the Miocene. They have arisen mainly through Pleistocene extinctions, speciation and dispersal, and some patterns are strongly linked to repeated glaciation. Endemic centres are associated with differentiated terrain and climates providing isolation, distinctive environments, and habitat continuity conducive to speciation.
Aim The flora characteristic of the Cape Floristic Region (CFR) is dominated by a relatively small number of clades that have been proposed as ‘Cape clades’. These clades have variously been suggested to have African or Austral affinities. Here we evaluate the support for these conflicting hypotheses. In addition, we test the hypothesis that these clades share a common time of differentiation from their geographical neighbours.
Location The Cape Floristic Region, South Africa
Methods We use both published and unpublished phylogenetic information to investigate the geographical sister areas of the Cape clades as well as the timing and the direction of biogeographical disjunctions.
Results Almost half of the Cape clades for which unambiguous sister areas could be established show a trans-Indian Ocean disjunction. The earliest trans-Indian Ocean disjunction dates from 80 Ma. Other disjunctions date from various times in the Cenozoic, and we suggest that the process of recruiting lineages into the Cape flora might be ongoing. Relatively few Cape clades show a sister relationship with South America and tropical Africa, despite their relative geographical proximity. Numerous Cape clades contain species also found on tropical African mountains; in all cases tested, these species are shown to be embedded within the Cape clades. While many Cape clades show a relationship with the Eurasian temperate flora, this is complicated by their presence in tropical Africa. The single case study addressing this to date suggests that the Cape clade is nested within a European grade.
Main conclusions Although many Cape clades show Austral rather than African relationships, there are numerous other patterns suggestive of a cosmopolitan flora. This spatial variation is echoed in the temporal data, from which, although there is wide variance around the dates of disjunctions, it is clear the Cape flora has been assembled over a long time period. There is no simple hypothesis that can account for the geographical sources of the currently distinctive Cape flora. The phylogenetic positions of Afromontane members of Cape clades suggest a history of dispersal from the CFR, rather than the reverse.
The recent proliferation of methodological advances in molecular phylogenetic and paleobiological research has resulted in powerful approaches to investigate the temporal framework of lineages. This article is a review of molecular and paleontological methods to estimate ages of clades. Inferring ages of clades is complicated by the nature of the process of molecular substitution and the uncertainties of the paleontological record. Some of the greatest problems associated with molecular methods include the stochastic nature of molecular substitution, the assumption of rate constancy among lineages when such constancy is absent, and the inextricable link between substitution rate and elapsed time on the branches of phylogeny. Molecular methods to estimate ages are ultimately based on the fact that as time elapses, molecular differences accumulate among sequences. Under rate constancy, methods to estimate ages include linear regression of molecular distance on elapsed time and maximum likelihood optimization of node ages under a single rate. Recently developed methods that allow rate heterogeneity are powerful approaches to estimate rates and divergence times under more realistic assumptions. Among-lineage rate variation is introduced as a compound Poisson process or more frequently is guided by the principle of temporal rate autocorrelation. These methods are based on numerical, semiparametric, and Bayesian parametric approaches, and some allow incorporation of constraints on the ages of nodes (derived, e.g., from fossils), conferring additional realism to age estimates. The paleontological record provides times of first appearances of morphological traits but not of lineage divergences; nevertheless, it represents one of the few sources of absolute information to decouple rates and times in a phylogeny. Analytical methods applied to paleontological data provide an alternative source of information about lineage duration. Stratigraphic confidence intervals that contain the time of origin of a lineage under a known probability are based on the frequency and abundance of fossil finds through the lineage's fossil record. Tests of postulated lineage durations, derived, for example, from a molecular age estimate, are available under probabilistic or likelihood frameworks. A powerful approach toward achieving more robust inferences about evolutionary rates and timing of lineage divergence lies in the complementary use of molecular-and paleontological-based approaches. While incorporating fossil information as age constraints confers further realism to molecular-estimated rates and ages, such estimates may be evaluated against expectations derived from paleontological information.
Cutler suggested almost 30 years ago that there was convergent evolution between African and Australian Restionaceae in the distinctive culm anatomical features of Restionaceae. This was based on his interpretation of the homologies of the anatomical features, and these are here tested against a ‘supertrec’ phylogeny, based on three separate phvlogenies. The first is based on morphology and includes all genera; the other two are based on molecular sequences from the chloroplast genome-, one covers the African genera, and the other tin-Australian genera. This analysis corroborates Cutler's interpretation of convergent evolution between African and Australian Restionaceae. However, it indicates that for the Australian genera, the evolutionary pathway of the culm anatomy is much more complex than originally thought. In the most likely scenario, the ancestral Restionaceae have protective cells derived from the chlorenchyma. These persist in African Restionaceae, but are soon lost in Australian Restionaceae. Pillar cells and sclerenchyma ribs evolve early in the diversification of Australian Restionaceae, but are secondarily lost numerous times. In some of the reduction cases, the result is a very simple culm anatomy, which Cutler had interpreted as a primitively simple culm type, while in other cases it appears as if the functions of the ribs and pillars may have been taken over by a new structure, protective cells developed from epidermal, rather than chlorenchyma, cells. Cutler suggested that this convergent evolution might have been in response to Tertiary climatic deterioration, but this study finds no strong corroborating evidence for this.
Phylogenetic analysis of nrDNA ITS and trnL (UAA) 5 exon-trnF (GAA) chloroplast DNA sequences from 17 species ofPelargonium sect.Peristera, together with nine putative outgroups, suggests paraphyly for the section and a close relationship between the highly disjunct South African and Australian species of sect.Peristera. Representatives fromPelargonium sectt.Reniformia, Ligularia s. l. andIsopetalum (the St. Helena endemicP. cotyledonis) appear to be nested within thePeristera clade. The close relationship between the South African and AustralianPeristera is interpreted as being caused by long-range dispersal to Australia, probably as recent as the late Pliocene.
A widely accepted paradigm for speciation in tropical forests, the refuge theory, requires periodic habitat fragmentation driven by global climatic fluctuations to provide conditions for allopatric speciation. This implies that comparative species richness in refugia is due to loss of diverse communities in areas affected by climatic cycles. In this study we compare distribution patterns of bird and plant taxa which we consider to be of either deep phylogenetic lineages or recent radiations. It is demonstrated that lowland areas which have been postulated as Pleistocene refugia are dominated by species which represent lineages of pre-Pleistocene age. Since variations in species richness within these forest tracts reflect currently apparent environmental variables which might be considered to determine carrying capacity, we do not need to postulate that richness is the result of changes in forest cover in the past. Recently diversified taxa of plants and birds are found mainly at the periphery of the main rain forest blocks and in habitat islands outside them. Here, peak concentrations of young restricted-range species are often congruent with clusters of old and biogeographically relictual species. It is suggested that this reflects special intrinsic environmental properties of these areas, in the form of long-term environmental stability caused mainly by persistent orographic rain or mist. In this case, richness is not necessarily due to extinction outside these areas. Stability not only enables survival of relictual taxa, but also promotes morphological differentiation of radiating taxa, leading to aggregates of taxa of restricted distribution.
Sites 1085, 1086 and 1087 were drilled off South Africa during Ocean Drilling Program (ODP) Leg 175 to investigate the Benguela Current System. While previous studies have focused on reconstructing the Neogene palaeoceanographic and palaeoclimatic history of these sites, palynology has been largely ignored, except for the Late Pliocene and Quaternary. This study presents palynological data from the upper Middle Miocene to lower Upper Pliocene sediments in Holes 1085A, 1086A and 1087C that provide complementary information about the history of the area. Abundant and diverse marine palynomorphs (mainly dinoflagellate cysts), rare spores and pollen, and dispersed organic matter have been recovered. Multivariate statistical analysis of dispersed organic matter identified three palynofacies assemblages (A, B, C) in the most continuous hole (1085A), and they were defined primarily by amorphous organic matter (AOM), and to a lesser extent black debris, structured phytoclasts, degraded phytoclasts, and marine palynomorphs. Ecostratigraphic interpretation based on dinoflagellate cyst, spore-pollen and palynofacies data allowed us to identify several palaeoceanographic and palaeoclimatic signals. First, the late Middle Miocene was subtropical, and sediments contained the highest percentages of land-derived organic matter, even though they are rich in AOM (palynofacies assemblage A). Second, the Late Miocene was cool-temperate and characterized by periods of intensified upwelling, increase in productivity, abundant and diverse oceanic dinoflagellate cysts, and the highest percentages of AOM (palynofacies assemblage C). Third, the Early to early Late Pliocene was warm-temperate with some dry intervals (increase in grass pollen) and intensified upwelling. Fourth, the Neogene “carbonate crash” identified in other southern oceans was recognized in two palynofacies A samples in Hole 1085A that are nearly barren of dinoflagellate cysts: one Middle Miocene sample (590 mbsf, 13.62 Ma) and one Upper Miocene sample (355 mbsf, 6.5 Ma). Finally, the extremely low percentages of pollen suggest sparse vegetation on the adjacent landmass, and Namib desert conditions were already in existence during the late Middle Miocene.
Environmental theories of African faunal evolution state that important evolutionary changes during the Pliocene–Pleistocene interval (the last ca. 5.3 million years) were mediated by changes in African climate or shifts in climate variability. Marine sediment sequences demonstrate that subtropical African climate periodically oscillated between markedly wetter and drier conditions, paced by earth orbital variations, with evidence for step-like (±0.2 Ma) increases in African climate variability and aridity near 2.8 Ma, 1.7 Ma, and 1.0 Ma, coincident with the onset and intensification of high-latitude glacial cycles. Analysis of the best dated and most complete African mammal fossil databases indicates African faunal assemblage and, perhaps, speciation changes during the Pliocene–Pleistocene, suggesting more varied and open habitats at 2.9–2.4 Ma and after 1.8 Ma. These intervals correspond to key junctures in early hominid evolution, including the emergence of our genus Homo. Pliocene–Pleistocene shifts in African climate, vegetation, and faunal assemblages thus appear to be roughly contemporary, although detailed comparisons are hampered by sampling gaps, dating uncertainties, and preservational biases in the fossil record. Further study of possible relations between African faunal and climatic change will benefit from the accelerating pace of important new fossil discoveries, emerging molecular biomarker methods for reconstructing African paleovegetation changes, tephra correlations between terrestrial and marine sequences, as well as continuing collaborations between the paleoclimatic and paleoanthropological communities.
Influx of aeolian pollen trapped in marine sediments off Namibia provides a wind variation record for the last 135 kyr. The influx of major pollen components is derived from the southwest African desert/semi-desert zone and shows six periods during which enhanced southeast trade winds contributed to strong upwelling and reduced sea surface temperatures. The most prominent of these occurred during 17–23 cal. kyr, 42–56 kyr and before 130 kyr B.P. Correspondence between the pollen influx record and the Vostok deuterium isotope record suggests that pronounced glacial Antarctic cooling was accompanied by intensification of the southeast trades throughout the Late Quaternary. However, during 42–23 kyr B.P. the combination of strong Antarctic glaciation with a decrease of wind zonality induced by low latitude precessional insolation changes caused strong alongshore winds and Ekman pumping that resulted in strong upwelling and reduced sea surface temperatures without pollen influx enhancement.
The ecological hypothesis of speciation is that reproductive isolation evolves ultimately as a consequence of divergent natural selection on traits between environments. Ecological speciation is general and might occur in allopatry or sympatry, involve many agents of natural selection, and result from a combination of adaptive processes. The main difficulty of the ecological hypothesis has been the scarcity of examples from nature, but several potential cases have recently emerged. I review the mechanisms that give rise to new species by divergent selection, compare ecological speciation with its alternatives, summarize recent tests in nature, and highlight areas requiring research.
The geography of speciation has long been contentious. In recent years, phylogenetic approaches have been proposed to determine the geographical mode of speciation. If reliable, these methods not only provide a means of settling the debate about the geography of speciation, but also indicate that sympatric speciation is surprisingly common and that peripatric speciation is relatively rare. Similar to any phylogenetic inference, reconstructions of speciation mode are only useful if the underlying assumptions of the method are met. In this case, the key assumption is that the geographical range of both extant and ancestral species at the time of speciation can be inferred from present-day distributions. We discuss whether, and under what circumstances, such assumptions could be met. We conclude that interspecific phylogenies are unable to test alternative hypotheses concerning the geography of speciation rigorously because of the lability of geographical ranges and the lack of correlation between the role of adaptive processes and geographical mode of speciation.
Dipsacales is an asterid angiosperm clade of ca. 1100 species, with most of its lineages occupying temperate regions of the Northern Hemisphere. A recent phylogenetic analysis based on 7593 nucleotides of chloroplast DNA recovered a well-resolved and strongly supported phylogenetic hypothesis, which we use here to estimate divergence times within the group. A molecular clock is strongly rejected, regardless of data partition. We used recently proposed methods that relax the assumption of rate constancy among lineages (local clocks, nonparametric rate smoothing, penalized likelihood, and Bayesian relaxed clock) to estimate the ages of major lineages. Age estimates for Dipsacales varied widely among markers and codon positions, and depended on the fossils used for calibration and method of analysis. Some methods yielded dates for the Dipsacales diversification that appear to be too old (prior to the presumed 125 my [million years] age of eudicots), and others suggested ages that are too young based on well-documented Dipsacales fossils. Concordant penalized likelihood and Bayesian studies imply that Dipsacales originated in the Cretaceous, as did its two major lineages, Adoxaceae and Caprifoliaceae. However, diversification of crown Adoxaceae and Caprifoliaceae mainly occurred in the Tertiary, with the origin of major lineages within these clades mainly occurring during the Eocene. Another round of diversification appears to have occurred in the Miocene. Several radiations, such as Valerianaceae in South America and Dipsacaceae around the Mediterranean, are even more recent. This study demonstrates the wide range of divergence times that can be obtained using different methods and data sets, and cautions against reliance on age estimates based on only a single gene or methodology. Despite this variance, significant conclusions can be made about the timing of Dipsacales evolution.
The Cape Floristic Region of South Africa is a global biodiversity hotspot. In 1998, a process of conservation planning began in the region that required quantitative targets for biodiversity. We combined new information and previously available data sets on biodiversity pattern and process to formulate targets for five groups of features: 102 broad habitat units (land types); locality records for 364 plant species in the family Proteaceae; locality records for 345 species of reptiles, amphibians and freshwater fish; estimated distributions and densities of 41 species of large and medium-sized mammals; and six types of spatial surrogates for ecological and evolutionary processes. We discuss our approach to formulating quantitative targets in the context of the general role of targets in conservation planning, the inadequacy of commonly used standard targets such as 10% of features or whole regions, and the uncertainties around setting targets for land types. We then describe our reasoning and methods for analysing data and identifying targets for each group of features. Our targets are not theoretical-they have been used to develop a regional conservation plan for which implementation is underway. Our targets are, however, provisional. Like any other conservation targets, they are estimates of the requirements for persistence of a region's biodiversity made within the constraints of limited information. We expect them to be improved in future reviews of appropriate targets for the Cape Floristic Region and elsewhere. Crown Copyright (C) 2003 Published by Elsevier Science Ltd. All rights reserved.
Phylogenetic relationships of the five families of the order Commelinales remain an area of deep uncertainty in higher-level monocot systematics, despite intensive morphological and anatomical study. To test the monophyly of the Commelinales and the subclass Commelinidae, evaluate their relationships, and analyze evolutionary trends in their morphology, ecology, and biogeography, we conducted parsimony analyses on 95 rbcL sequences representing 17 taxa of Commelinales, 16 taxa of other Commelinidae, and 63 taxa from Arecidae, Liliidae, and Zingiberidae. Commelinales is polyphyletic and Commelinidae paraphyletic, with Eriocaulaceae and Xyridaceae sister to Poaceae and its relatives, Rapateaceae sister to Bromeliaceae and Mayacaceae, and Commelinaceae sister to Philydrales and allies. Thurnia is sister to Prionium at the base of Cyperaceae-Juncaceae; only 1 of Cronquist's multifamily commelinoid orders is diagnosed as monophyletic. We propose a revised Commelinidae, incorporating 4 revised superorders (Bromelianae, Commelinanae, Dasypogonanae, Arecanae) and 10 orders ((Poales, Eriocaulales, Cyperales, Typhales, Bromeliales), (Commelinales, Philydrales, Zingiberales), (Dasypogonales), (Arecales)). Morphological and anatomical characters used to define the original Commelinales and Commelinidae appear to be plesiomorphic or to reflect convergence or recurrent mutation; several characters supporting our revised classification are anatomical traits that seem relatively insulated from environmental selection pressures. The Commelinidae distal to the Arecales arose in South America, with amphiatlantic Bromeliaceae-Mayacaceae-Rapateaceae originating in the Guayana Shield. Ecological diversification involved the repeated invasion of shady, infertile, or arid microsites. The numbers of species in families of the revised Commelinidae are related partly to the extent of adaptive radiation in those families, but seem more strongly related to nonadaptive features promoting speciation, such as restricted seed dispersal (especially in forest interior groups with fleshy fruits), polyploidy, aneuploidy, and apomixis. Species diversity is unrelated to the rate/amount of rbcL sequence evolution.
The long-standing notion that most angiosperm flowers are specialized for pollination by particular animal types, such as birds or bees, has been challenged recently on the basis of apparent widespread generalization in pollination systems. At the same time, biologists working mainly in the tropics and the species-rich temperate floras of the Southern hemisphere are documenting pollination systems that are remarkably specialized, often involving a single pollinator species. Current studies are aimed at understanding: (1) the ecological forces that have favoured either generalization or specialization in particular lineages and regions; (2) the implications for selection on floral traits and divergence of populations; and (3) the risk of collapse in plant-pollinator mutualisms of varying specificity.
Systematic conservation planning is a branch of conservation biology that seeks to identify spatially explicit options for the preservation of biodiversity. Alternative systems of conservation areas are predictions about effective ways of promoting the persistence of biodiversity; therefore, they should consider not only biodiversity pattern but also the ecological and evolutionary processes that maintain and generate species. Most research and application, however, has focused on pattern representation only. This paper outlines the development of a conservation system designed to preserve biodiversity pattern and process in the context of a rapidly changing environment. The study area is the Cape Floristic Region (CFR), a biodiversity hotspot of global significance, located in southwestern Africa. This region has experienced rapid (post-Pliocene) ecological diversification of many plant lineages; there are numerous genera with large clusters of closely related species (flocks) that have subdivided habitats at a very fine scale. The challenge is to design conservation systems that will preserve both the pattern of large numbers of species and various natural processes, including the potential for lineage turnover. We outline an approach for designing a system of conservation areas to incorporate the spatial components of the evolutionary processes that maintain and generate biodiversity in the CFR. We discuss the difficulty of assessing the requirements for pattern versus process representation in the face of ongoing threats to biodiversity, the difficulty of testing the predictions of alternative conservation systems, and the widespread need in conservation planning to incorporate and set targets for the spatial components (or surrogates) of processes.
The Cape flora of South Africa grows in a continental area with many diverse and endemic species. We need to understand the evolutionary origins and ages of such 'hotspots' to conserve them effectively. In volcanic islands the timing of diversification can be precisely measured with potassium-argon dating. In contrast, the history of these continental species is based upon an incomplete fossil record and relatively imprecise isotopic palaeotemperature signatures. Here we use molecular phylogenetics and precise dating of two island species within the same clade as the continental taxa to show recent speciation in a species-rich genus characteristic of the Cape flora. The results indicate that diversification began approximately 7-8 Myr ago, coincident with extensive aridification caused by changes in ocean currents. The recent origin of endemic species diversity in the Cape flora shows that large continental bursts of speciation can occur rapidly over timescales comparable to those previously associated with oceanic island radiations.
The sudden, widespread glaciation of Antarctica and the associated shift towards colder temperatures at the Eocene/Oligocene boundary (approximately 34 million years ago) (refs 1-4) is one of the most fundamental reorganizations of global climate known in the geologic record. The glaciation of Antarctica has hitherto been thought to result from the tectonic opening of Southern Ocean gateways, which enabled the formation of the Antarctic Circumpolar Current and the subsequent thermal isolation of the Antarctic continent. Here we simulate the glacial inception and early growth of the East Antarctic Ice Sheet using a general circulation model with coupled components for atmosphere, ocean, ice sheet and sediment, and which incorporates palaeogeography, greenhouse gas, changing orbital parameters, and varying ocean heat transport. In our model, declining Cenozoic CO2 first leads to the formation of small, highly dynamic ice caps on high Antarctic plateaux. At a later time, a CO2 threshold is crossed, initiating ice-sheet height/mass-balance feedbacks that cause the ice caps to expand rapidly with large orbital variations, eventually coalescing into a continental-scale East Antarctic Ice Sheet. According to our simulation the opening of Southern Ocean gateways plays a secondary role in this transition, relative to CO2 concentration.
The flora of the south-western tip of southern Africa, the Cape flora, with some 9000 species in an area of 90,000 km2 is much more speciose than can be expected from its area or latitude, and is comparable to that expected from the most diverse equatorial areas. The endemism of almost 70%, on the other hand, is comparable to that found on islands. This high endemism is accounted for by the ecological and geographical isolation of the Cape Floristic Region, but explanations for the high species richness are not so easily found. The high species richness is accentuated when its taxonomic distribution is investigated: almost half of the total species richness of the area is accounted for by 33 'Cape floral clades'. These are clades which may have initially diversified in the region, and of which at least half the species are still found in the Cape Floristic Region. Such a high contribution by a very small number of clades is typical of island floras, not of mainland floras. The start of the radiation of these clades has been dated by molecular clock techniques to between 18 million years ago (Mya) (Pelargonium) and 8 Mya (Phylica), but only six radiations have been dated to date. The fossil evidence for the dating of the radiation is shown to be largely speculative. The Cenozoic environmental history of southern Africa is reviewed in search of possible triggers for the radiations, climatic changes emerge as the most likely candidate. Due to a very poor fossil record, the climatic history has to be inferred from larger scale patterns, these suggest large-scale fluctuations between summer wet (Palaeocene, Early Miocene) and summer dry climates (Oligocene, Middle Miocene to present). The massive speciation in the Cape flora might be accounted for by the diverse limitations to gene flow (dissected landscapes, pollinator specialisation, long flowering times allowing much phenological specialisation), as well as a richly complex environment providing a diversity of selective forces (geographically variable climate, much altitude variation, different soil types, rocky terrain providing many micro-niches, and regular fires providing both intermediate disturbances, as well as different ways of surviving the fires). However, much of this is based on correlation, and there is a great need for (a) experimental testing of the proposed speciation mechanisms, (b) more molecular clock estimates of the age and pattern of the radiations, and (c) more fossil evidence bearing on the past climates.
Phylogenetic analyses of four plastid DNA regions, the rbcL exon, trnL intron, trnL-trnF intergenic spacer, and rps16 intron from each of 73 species in the African genus Moraea (Iridaceae: Irideae) including accessions of all major species clusters in the genus, show Moraea to be paraphyletic when Barnardiella, Galaxia, Hexaglottis, Homeria (all southern African), and Gynandriris (Eurasian as well) were recognized as separate genera. There are several small, isolated species clusters at the basal nodes of the tree that are all restricted to the winter-rainfall zone of southern Africa (the Greater Cape floral kingdom) and a few, highly derived, large species groups that have radiated extensively within the winter-rainfall zone. Mapping of floral traits shows that an Iris-type flower is ancestral in Moraea. Floral changes are associated with shifts in pollination systems, either from passive pollen deposition on long-tongued bees foraging for nectar to active pollen collection by female bees foraging for pollen, fly, or hopliine scarab beetle pollination. Dating the nodes of the phylogenetic tree using non-parametric rate smoothing with a calibration point derived from broad dating of the angiosperms indicates that the divergence between Moraea and its sister genus Ferraria occurred about 25 mya in the early Miocene. The early radiation of Moraea took place against a background of aridification and the spread of open habitats, such as desert, shrubland, and fynbos.