Article

Effects of mistletoe on diversity: A case-study from southern New South Wales

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Abstract

The influence of mistletoe density on avian diversity has been noted previously, with several studies demonstrating a close positive relationship between the two variables. All previous work has been correlative, exploiting naturally occurring variation in mistletoe density, and hence unable to demonstrate a causative link between mistletoe density and avian richness. Here I compare the avifauna of two adjacent woodland remnants, one of which has had most mistletoe plants removed, but otherwise comparable in area, vegetation and grazing history. Ten-hour inventories were conducted in each remnant in both spring and summer, resulting in a total of 40 hours of censuses. Of the 71 species recorded overall, 52 were recorded from the treatment site (with reduced mistletoe density) and 61 species from the control site. Significantly more woodland-dependent species and species known to feed on mistletoe were recorded in the control site, while there was no significant difference for those species known to nest in mistletoe. These results broadly support the idea that mistletoe is a keystone resource, with mistletoe density having a significant positive effect on species richness. These findings reinforce previous correlative studies, and further highlight the importance of mistletoe in Australian woodlands and forests.

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... The importance of canopy organisms and processes is becoming increasingly recognised in relation to understanding biodiversity and ecosystem processes in a globalchange context (Nakamura et al., 2017). inhabiting the canopies (Watson, 2001(Watson, , 2002Thomsen et al., 2018). ...
... Honeybees (Aparicio et al., 1995;Sipes et al., 2014), ies (Player, 1979;Aparicio et al., 1995;Wiesenborn, 2016), and ants ( S4) and fruit available in the pine forest during some periods. In this sense, mistletoe behaves as a secondary foundation species in the organisation of the pine forest ecosystem that it inhabits, inducing changes that are disproportionate to the plant's abundance and biomass, thereby favouring local and regional wildlife diversity (Watson, 2001(Watson, , 2002Watson & Herring, 2012;Mellado & Zamora, 2017). Although Viscum album has traditionally been considered a pest of its pine hosts, it increases the heterogeneity of the forest canopy by providing resources for a new community of consumers. ...
... This 87 work clearly exemplies the mismatch outlined by Watson (2001) between considering mistletoe as a pest that needs to be controlled vs. considering it a keystone species that provides new opportunities for species and ecological interactions. Now widespread evidence characterises mistletoe as a keystone resource, boosting diversity in many ecosystems, such as eucalypt forests of southeastern Australia (Watson, 2001(Watson, , 2002Watson & Herring, 2012), mesquite woodland of the southwestern USA (Anderson & Anderson, 1973), tropical forests in India (Davidar, 1985;Ali & Ripley, 1999) and South America (Fadini et al., 2018), and cactusdominated deserts of Chile Medel, 2000). ...
Thesis
In this thesis, a study is made of the different roles that the European mistletoe (Viscum album subsp. austriacum) can play simultaneously in a Mediterranean pine forest, and their ecological consequences generating multiple plant–plant and plant–animal interactions in their ecosystem. Due to their hemiparasitic nature, the mistletoe has been traditionally regarded as a host pathogen, causing detrimental effects on growth, morphology, and reproduction. However, recently other ecological interactions that mistletoe establishes in the forest ecosystem have been found to be noteworthy, not only with its host but also with the rest of the community where they live. Consequently, the presence of mistletoe in the forest canopy can cause direct and indirect effects in their ecosystem through trophic and non– trophic relationships, favoring the restructure of community composition. Therefore, this thesis has been split into three main parts examining the role of mistletoe: I) as a keystone resource for its associated arthropods (Chapters 1–3); II) as direct competitor with its host (Chapters 4–5); and III) as indirect competitor with host–feeding herbivores (Chapter 6) and facilitator for the herbaceous community (Chapter 7). From a holistic view, it is concluded that mistletoes are keystone species that trigger a series of interactions with important ecological consequences at the community level, causing direct and indirect effects at different trophic levels. This has profound implications for the dynamics of the forest ecosystem, restructuring the entire community, from nutrient dynamics and herbaceous community to primary and secondary consumers. Thus, by simultaneously providing new resources while acting as a competitor and facilitator, mistletoes become ecosystem engineers, building an additional level of heterogeneity to the forest canopy and amplifying biodiversity and complexity in their ecosystem.
... Yet, these parasites also provide consumers with new resources other than those of the host and therefore boost the overall diversity of species and ecological interactions (Lázaro-González et al., 2017). The resulting association between trees and parasitic plants is thus a useful system in which to assess the contribution of secondary foundation species in fostering plant-animal interactions and assembly rules of communities inhabiting the canopies (Watson 2001(Watson , 2002Thomsen et al., 2018). ...
... In addition, because of their long-lived habit, constant and predictable reproduction due to its hemiparasite habit, mistletoe constitutes a reliable food resource, being the only source of flowers (Supporting Information S1, Fig. S2) and fruit available in the pine forest during some periods. In this sense, mistletoe behaves as a secondary foundation species in the organisation of the pine forest ecosystem that it inhabits, inducing changes that are disproportionate to the plant's abundance and biomass, thereby favouring local and regional wildlife diversity (Watson, 2001(Watson, , 2002Watson & Herring, 2012;Mellado & Zamora, 2017). Although Viscum album has traditionally been considered a pest of its pine hosts, it increases the heterogeneity of the forest canopy by providing resources for a new community of consumers. ...
... This work clearly exemplifies the mismatch outlined by Watson (2001) between considering mistletoe as a pest that needs to be controlled vs. considering it a keystone species that provides new opportunities for species and ecological interactions. Now widespread evidence characterises mistletoe as a keystone resource, boosting diversity in many ecosystems, such as eucalypt forests of southeastern Australia (Watson, 2001(Watson, , 2002Watson & Herring, 2012), mesquite woodland of the southwestern USA (Anderson & Anderson, 1973), tropical forests in India (Davidar, 1985;Ali & Ripley, 1999) and South America (Fadini et al., 2018), and cactus-dominated deserts of Chile (Martínez del Rio et al., 1996;Medel, 2001). ...
Article
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• Forest canopies provide the initial physical and biological framework to secondary, dependent species, such as parasitic plants. In a Mediterranean pine forest, we have taxonomically and functionally characterised the entire arthropod community that interacts with mistletoe during its flowering period. • We hypothesise that a secondary foundation species such as mistletoe enhances the arthropod diversity and abundance, fostering novel plant–animal interactions in the canopy. Our results clearly show contrasting guilds of herbivores (highly specialised) and floral visitors (highly generalist) with markedly different taxonomic and ecological profiles, the latter determining the fruit set of the mistletoe. • By acting as a secondary foundation species, mistletoe, during flowering, increases the diversity and abundance of newcomers in the pine canopy. New species attracted to the canopy include a specialised herbivore, Cacopsylla visci , and a diverse guild of floral visitors, including the orders Hymenoptera, Diptera, Hemiptera, and Lepidoptera. • In conclusion, mistletoe creates conditions that support the co‐occurrence of functionally distinct organisms in the canopies, fostering pine forest biodiversity and complexity of ecological interactions.
... Yet, these parasites also provide consumers with new resources other than those of the host and therefore boost the overall diversity of species and ecological interactions (Lázaro-González et al., 2017). The resulting association between trees and parasitic plants is thus a useful system in which to assess the contribution of secondary foundation species in fostering plant-animal interactions and assembly rules of communities inhabiting the canopies (Watson 2001(Watson , 2002Thomsen et al., 2018). ...
... In addition, because of their long-lived habit, constant and predictable reproduction due to its hemiparasite habit, mistletoe constitutes a reliable food resource, being the only source of flowers (Supporting Information S1, Fig. S2) and fruit available in the pine forest during some periods. In this sense, mistletoe behaves as a secondary foundation species in the organisation of the pine forest ecosystem that it inhabits, inducing changes that are disproportionate to the plant's abundance and biomass, thereby favouring local and regional wildlife diversity (Watson, 2001(Watson, , 2002Watson & Herring, 2012;Mellado & Zamora, 2017). Although Viscum album has traditionally been considered a pest of its pine hosts, it increases the heterogeneity of the forest canopy by providing resources for a new community of consumers. ...
... This work clearly exemplifies the mismatch outlined by Watson (2001) between considering mistletoe as a pest that needs to be controlled vs. considering it a keystone species that provides new opportunities for species and ecological interactions. Now widespread evidence characterises mistletoe as a keystone resource, boosting diversity in many ecosystems, such as eucalypt forests of southeastern Australia (Watson, 2001(Watson, , 2002Watson & Herring, 2012), mesquite woodland of the southwestern USA (Anderson & Anderson, 1973), tropical forests in India (Davidar, 1985;Ali & Ripley, 1999) and South America (Fadini et al., 2018), and cactus-dominated deserts of Chile (Martínez del Rio et al., 1996;Medel, 2001). ...
Article
Full-text available
1. The colonisation of a new habitat by a community is led by deterministic and stochastic processes at different spatio‐temporal scales. Parasitic plants, such as mistletoe, represent a new habitat within forest canopy that is free to be colonised by many organisms. 2. This study investigates how ecological factors operating at forest and plant scales drive changes in both specialist (mistletoe‐dwelling) and tourist (transient visitors) arthropod communities inhabiting European mistletoe, Viscum album subsp. austriacum, in a Mediterranean pine forest. The influence of elevation along a broad elevational gradient was tested by sampling arthropod communities dwelling in mistletoe plants and host pine branches and the effects of mistletoe plant size, distances to other mistletoes, and temporal variation in arthropod assemblages inhabiting mistletoes. 3. The diversity of the specialist community remained constant along the elevational gradient and over the summer period, while the tourist and pine‐dwelling arthropod communities showed species turnover. Larger mistletoes were occupied by more species and individuals, whereas more isolated mistletoes presented the same equilibrium point as the more aggregated ones. Thus, mistletoe size is key to the composition of the arthropod community. 4. In conclusion, this study's findings indicate contrasting assembly rules for specialised and tourist arthropod communities associated with mistletoe. The specialist community was highly stable and followed a deterministic trophic sequence of colonisation as the assemblage rule: first, colonisation by the main specialist herbivore, Cacopsylla visci, and, second, by its predator Anthocoris visci. Meanwhile, the tourist community, being a subset of the arthropod assemblage of the pine, acts independent of mistletoe presence.
... Similarly, the litter of the root parasite Bartsia alpina L. was found to increase the growth (~50 %) of two commonly co-occurring species, Betula nana L. and Poa alpina L. (Quested et al., 2003a). In addition, the introduction of nutrients along with the patchy occurrence of hemiparasites has potential to increase the spatial heterogeneity of soil nutrients enhancing local plant community richness (Watson, 2002;March, 2007). Further, this increase in resource patchiness may drive small-scale heterogeneity in productivity and food availability for animals resulting in increased species richness (e.g., birds, Watson and Herring, 2012). ...
... Mistletoes are a diverse group of aerial parasitic plants occurring in all terrestrial vegetation types (Kuijt, 1969), which alter nutrient availability and the structure and composition of plant and animal assemblages (Watson, 2001(Watson, , 2002(Watson, , 2009March andWatson, 2007, 2010;Watson and Herring, 2012;Ndagurwa et al., 2013Ndagurwa et al., , 2014. They draw up nutrients and water from the host xylem by maintaining higher transpiration rates than their hosts (Ehleringer and Marshall, 1995), potentially altering host tree water use. ...
... Parasitic plants have been found to influence host water use (Sala et al., 2001), species richness (e.g. birds and mammals, Watson, 2001Watson, , 2002Shaw et al., 2004;Watson, 2009;Watson and Herring, 2012), and soil microbial communities (Cullings et al., 2005;Mueller and Gehring 2006;Cullings and Hanely, 2010) in a range of systems. Consistent with these studies, this study shows that mistletoes alter soil moisture content and the litter layer insect abundance and diversity in semi-arid savanna. ...
Thesis
Full-text available
Parasitic plants are nutrient parasites and thus are expected to influence nutrient cycling in environments where they occur. However, the role of parasitic plants has largely been ignored in many studies of nutrient cycling. This thesis investigated the effects of hemiparasitic mistletoes, i.e. Erianthemum ngamicum (Sprague) Danser (Loranthaceae), Plicosepalus kalachariensis (Schinz) Danser (Loranthaceae) and Viscum verrucosum Harv. (Viscaceae), on nutrient cycling in an Acacia dominated semi-arid savanna woodland in southwest Zimbabwe. Since litterfall is the major pathway for the transfer of carbon and nutrients from plants to the soil, this study assessed the influence of mistletoes on litterfall, nutrient transfer, decomposition and the subsequent effects on soil nutrient concentrations. First, I investigated the patterns of mistletoe infection of Acacia trees and tested the relationship between tree size (measured as tree height and trunk diameter) and mistletoe infection intensity. Mistletoe infections were significantly greater in the larger A. robusta trees than in A. gerrardii, A. karroo and A. nilotica. Large trees had more mistletoe infections than small trees, and this was true for P. kalachariensis and V. verrucosum but not for E. ngamicum. Similarly, in experimentally disinfected trees, mistletoe reinfections were higher in large than small trees. As a result, there was a positive relationship between mistletoe infection and tree size. However, these relationships were generally weak suggesting that tree size may explain differences in mistletoe infection among host Acacia species but other factors may be important in determining mistletoe infection. Given that litterfall and nutrient transfers are driven by the traits of individual plant species, different plant species can be expected to make different contributions to nutrient cycling. Litterfall and nutrient transfers varied among the study species, with results showing that E. ngamicum and P. kalachariensis and to a lesser extent V. verrucosum increase litterfall and nutrient transfers and the effects were greater at high mistletoe density. The increase in nutrient returns was due to both the effect of enriched mistletoe litter and increased volumes of litterfall beneath host trees. Associated with these changes in litterfall was an increase in the abundance and diversity of the litter-layer insects. Additionally, the soil moisture content and bacterial and fungal colony numbers changed with mistletoe infection. These changes were considered to alter litter processing rates, and consequently decomposition and overall nutrient cycling. However, there was little evidence to suggest that they had an effect on litter decomposition. Nevertheless, the high quality mistletoe litters, particularly V. verrucosum, decomposed and released nutrients faster than A. karroo litter. Nutrient release patterns varied among the mistletoe species, with the loss of N, P and C being higher in E. ngamicum, V. verrucosum and P. kalachariensis, respectively. As a result, mistletoe infection was associated with elevated soil nutrient concentrations, also with higher concentrations at high mistletoe density. Similarly, soil nitrogen (N) transformations and mineral N increased with mistletoe infection but were greatest beneath trees infected by E. ngamicum and litter quality, i.e. the condensed tannin, lignin and lignin/N content, was shown to regulate soil N transformations. These findings show that mistletoes significantly enhance nutrient cycling in semi-arid savanna, which supports the notion that mistletoes can substantially influence nutrient availability to other plants. The variation in nutrient cycling attributes among mistletoe species and with mistletoe density along with the patchy distribution of mistletoes was considered to increase the spatial heterogeneity of nutrient availability with important implications for the structure and function of this semi-arid savanna ecosystem. The findings reported herein along with findings in other systems that contain hemiparasites suggest that enhanced nutrient cycling may be a general property of hemiparasites.
... Likewise, most parasitic plant groups use animals (generalist nectarivorous birds and insects) as pollen vectors, rewarding pollinators with abundant nectar rich in available carbohydrates. Finally, their nutrient and waterrich foliage is widely consumed by mammalian and arthropod folivores (Watson 2001(Watson , 2009, with increased prey availability (especially herbivorous insects; Anderson & Braby 2009;Burns, Cunningham & Watson 2011) potentially having indirect effects on higher trophic levels, especially spiders (Burns 2009, Halaj, Ross & Moldenke 2000Shaw, Watson & Mathiason 2004) and insectivorous birds (Turner 1991;Watson 2002). ...
... While observational and experimental data with aerial hemiparasites have documented positive relationships between mistletoe density and avian species richness (Bennetts et al. 1996;Watson 2002;Mathiasen et al. 2008), it is unclear which resources contribute to this response -structure, direct nutritional resources (leaves, fruit, nectar) or indirect nutritional resources (foliar arthropods, litter-dwelling prey). Previous studies have used either natural variation in parasite density (e.g. ...
... Turner 1991;Bennetts et al. 1996) or patch-scale removal experiments (e.g. Watson 2002;Watson & Herring 2006) and, although reporting broad-based changes in diversity and community composition associated with hemiparasite occurrence, they have been unable to attribute recorded variation in richness with particular resources. Moreover, background variation in the same structural and nutritional resources is rarely considered, preventing estimation of the community-level influence of parasitic plants on resource availability and constraining our understanding of their ecological function. ...
Article
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1. Parasitic plants are components of many habitats and have pronounced effects on animal diversity; shaping distributions, influencing movement patterns and boosting species richness. Many of these plants provide fleshy fruit, nectar, foliar arthropods and secure nest sites, but the relative influence of these nutritional and structural resources on faunal species richness and community structure remains unclear. 2. To disentangle these factors and quantify the resources provided by parasitic plants, we focused on the hemiparasitic shrub Exocarpos strictus (Santalaceae). Twenty-eight Eucalyptus camaldulensis forest plots were studied in the Gunbower-Koondrook forest in southeastern Australia, comparing riparian forests with an Exocarpos-dominated understorey with otherwise similar habitats with or without equivalent cover of the non-parasitic Acacia dealbata. Analyses of avian richness and incidence (overall and in six feeding guilds) were complemented by explicit measures of resources in both shrub types; foliage density, standing crop of fleshy fruit and foliar arthropod abundance and biomass. 3. Avian species richness was c. 50% greater and total incidences for five guilds were significantly greater in forests with the parasitic shrub, with no appreciable differences between the other two habitat types. In addition to plentiful fleshy fruits, Exocarpos supported abundant arthropods in their foliage – significantly higher in biomass than for equivalent volumes of Acacia foliage. Exocarpos had a shorter and denser structure, providing a greater range of microhabitats than the more open growing Acacia. 4. Our results demonstrate that structural and nutritional resources (both direct and indirect) provided by Exocarpos affect diversity and community composition, with each set of resources affecting different organismal groups. Rather than an exceptional system or an aberrant result, we suggest the influence of Exocarpos on species richness relates to their parasitic habit, supporting the hypothesis that parasitic plants mobilize resources from their hosts and make them available to a range of trophic levels.
... They exert considerable impacts on multiple trophic levels within communities, affecting population dynamics, diversity, and distributions of other plants as well as invertebrates, birds, and mammals (Press and Phoenix 2005;Barea and Watson 2007;Bowen et al. 2009;Watson 2016). Their broad geographic distributions and long and unique flowering and fruiting periods make them an attractive resource for wildlife, and they provide structural and nutritional resources within canopies (Barlow 1983;Watson 2002Watson , 2004Cooney and Watson 2005;Barea 2008;Napier et al. 2014;Watson 2015;Sayad et al. 2017). ...
... The adverse effects of parasitism on trees have concerned ecologists and agroforesters, as the direct use of host resources and physiological consequences caused by mistletoes make them potentially damaging to the host plants (Mathiasen et al. 1990;Watson 2002;Dobbertin and Rigling 2006;Way 2011;Henriquez-Velasquez et al. 2012;Edagbo et al. 2012a;Sangüesa-Barreda et al. 2012;Kolb et al. 2016;Mutlu et al. 2016;Gebriel 2017). However, some studies suggest that mistletoe infection may also have benefits to their host plants by the indirect benefit of attracting potential pollinators, seed dispersers, and insectivores for the parasitised host, so improving the rate of visitation to the host (Van Ommeren and Whitham 2002; Carlo and Aukema 2005;Cooney and Watson 2005;Bowen et al. 2009;Watson 2009;Ndagurwa et al. 2016). ...
Article
The relationship between mistletoes and their host trees constitutes one of the unique host–parasite interactions in ecosystems. Most West African studies have reported on the parasitic nature of the relationship between Tapinanthus dodoneifolius mistletoes and Parkia biglobosa trees. However, there is little on bird species’ use and subsequent dispersal of the mistletoe on P. biglobosa, and consequently, we investigated aspects of this relationship in the present study. We conducted our study in Amurum Forest Reserve, located in the central part of Nigeria, from May to September 2017. The study area consists of a mosaic of savanna, gallery forest, and rocky outcrops. Of the bird community in this area, the yellow-fronted Tinkerbird Pogoniulus chrysoconus had the highest number of visits to T. dodoneifolius fruits, while the Senegal Eremomela Eremomela pusilla spent the most time foraging on the fruits. Four sunbird species were recorded feeding on T. dodoneifolius flowers for nectar; all but the Copper Sunbird Cinnyris cupreus were observed opening the flowers of T. dodoneifolius. Other bird species were recorded foraging on insects on T. dodoneifolius, and some simply perching on twigs or pecking on mistletoe fruits. This was a mutualistic relationship between the respective bird species and the mistletoe. This indirectly benefitted the parasitised host by attracting potential pollinators, seed dispersers, and insectivores for the host, hence, improving the rate of visitation to the host. These patterns of visitation behaviours highlighted the ecological importance of T. dodoneifolius within the reserve, particularly in enhancing the survival of other taxa within the reserve. Findings from this study contribute to developing more-nuanced conservation strategies for mixed high savannah habitat types across the tropics.
... If mistletoes are to be managed and threatened species conserved, their population biology must be sufficiently well understood to formulate management strategies. Furthermore, most of the studies about mistletoe are from Australia and New Zealand (Ladley and Kelly, 1996;Norton and De Lange, 2002;Stafford-Smith, 1998 cited in Clyde andCarol, 1995;Watson, 2002). According to Watson (2001), tropical regions are underrepresented in the mistletoe literature. ...
... This is because of the presence of branches in the canopy layer that may result in accumulation of dusts, which encourages mistletoes plants to grow (Kartoolinejad et al., 2007). Mistletoes that prefer the upper portions of their host tree canopies may have higher light requirements than those in the lower parts of the canopies, or they may be more tolerant of lower humidity, and/or greater degree of drought stress (Watson et al., 2002). The lower tree trunk has been reported to contain the lowest mistletoes diversity. ...
... Indeed, we proposed that mistletoe functions as a keystone resource, having a disproportionately positive influence on diversity patterns in woodlands and forests worldwide (Watson 2001). A comparison of two woodlands near Canberra (one of which had been cleared of all mistletoe for five years but otherwise similar in all respects) revealed that mistletoe boosted the richness of woodland bird species by approximately 20% (Watson 2002b)-strong evidence that mistletoe can have a substantial direct effect on biodiversity. ...
... Through a combination of fire suppression, fewer leaf-eating marsupials (known to favour mistletoe foliage, Watson 2001;2004a), and the increased availability of water, nutrients and light in woodlands (especially associated with edge habitats), mistletoe density has increased 10-100 fold in many regions. So, while fragmentation continues to cause widespread declines in woodland biota, mistletoe may be a key factor allowing woodland-dependent animals to persist in the remainder of their habitat, providing critical food and shelter in an otherwise resource-poor ecosystem (Watson 2002b). Moreover, unlike hollows and coarse woody debris that may take centuries to develop, mistletoe responds more rapidly and can therefore be manipulated more easily. ...
Article
Mistletoe is a prominent component of woodlands throughout south-eastern Australia. Unlike many woodland plants and animals that are becoming increasingly scarce, mistletoe has responded positively to habitat fragmentation and has become more abundant in many areas. These parasitic plants are widely regarded as introduced pests that kill trees and degrade the landscape, yet our research is revealing quite a different story. All mistletoes in Australia are native and they engage in a range of interactions with many animals, having a positive influence on overall biodiversity. Yet, in high densities mistletoes can be detrimental to individual trees and, in extremely high densities, they can contribute to premature tree mortality. Accordingly, we need to understand better the role of mistletoe in remnant woodlands and determine mistletoe densities that achieve these biodiversity benefits without compromising the long-term viability of tree populations. To address this issue, we are conducting a large-scale investigation in the upper Billabong Creek catchment near Holbrook, NSW known as the RIFLE study (Resources in Fragmented Landscapes Experiment). Forty grassy box woodland remnants occurring on private land were selected and surveyed for all terrestrial vertebrates over 12 months. All mistletoes were then removed from twenty of the remnants, leaving the other twenty as controls. Over the next two decades, biodiversity will be compared in these two groups of fragments, with birds, mammals, reptiles and butterflies monitored seasonally and related to a range of resources. Preliminary data indicate that mistletoe provides critical nutritional and nesting resources for many animals, determining distributions for many species and potentially offsetting many of the deleterious consequences of habitat fragmentation. Mistletoe also plays a key role in nutrient dynamics, affecting litter and soil composition which may modify stand-level productivity and successional processes. Rather than a threatening process or a weed that should be controlled, mistletoe appears to be crucial to the ongoing maintenance and conservation of our threatened woodlands. While our research is focused on mistletoe in remnant woodlands, the implications of our work extend much further. Our long term aim is to inform restoration and rehabilitation efforts, augmenting existing practices and giving resource managers the process-based knowledge required to implement on-ground works designed for maximum ecological benefit.
... Moreover, the vastness of burnt areas, and the likelihood that adjacent seed sources had burnt before hosts in the original area had regenerated, often seemed to prohibit mistletoe recovery. Thus, it appeared that current fire regimes could be threatening a guild of plants of considerable ecological importance (e.g. Watson 2001 Watson , 2002). The objectives of this study were to establish the effects of fire on mistletoes and to investigate the mechanisms that have enabled them to persist in the Pilbara's arid, fire-prone environments. ...
... They are often the principal pollinators (e.g. Reid 1989 Reid , 1990 Watson 1997 Watson , 2002 Higgins et al. 2001) and they, too, are important to other plant species on which they feed. Finally it should be noted that the loss of mistletoes and mistletoe-dependent species can have a cascading effect on regional biodiversity. ...
Article
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Between 1982 and 2008, data were collected on Loranthaceous mistletoes, their hosts and the fire responses of both, in and adjacent to the Pilbara, an arid region in Western Australia where hummock grasslands (dominated by Triodia sp. R.Br., Poaceae) and mulga woodlands (dominated by Acacia aneura Benth., Mimosaceae) are widespread. Hummock grasslands are fire prone and highly flammable. Mulga woodlands are less so, except in an inter-zone where Triodia in the understorey may be sufficiently dense to carry fire. The foliage (and fresh seed) of all mistletoe species was killed if scorched. Moreover, none had any means of long-term, in situ seed-storage. Three fire-survival strategies were observed across the 16 mistletoe taxa. One species (two varieties) was a resprouter. The other 14 were obligate seeders. Post-fire regeneration of those taxa depended on fresh seed being imported and deposited in suitable host canopies by birds. Twelve of them reduced fire risk by varying degrees of host specificity, favouring hosts that grew in fire-sheltered sites. However, two species had very low host specificity and grew on fire-vulnerable hosts in fire-prone hummock grasslands. Their low host specificity increased the likelihood that imported seed would be deposited on suitable hosts. Since pastoral settlement, fire regimes have changed and current regimes are eroding many mistletoe populations. None of the species occurring in the study area is threatened at bioregional or National levels. Nevertheless, the outlook is bleak for mistletoes growing in areas dominated by hummock grasslands, subregional extinction is likely and there are broader implications for biodiversity.
... Rather than operating independently, the effects of parasitic plants on resource provision, nutrient availability, habitat structure, and microclimate are additive and interacting; their combined in uence on ecological communities is best quanti ed by controlled comparisons of species composition and diversity (Lafferty et al. 2006, Watson 2016). An increasing number of these comparative studies are available, uni ed by ndings of strong positive in uences of parasitic plant occurrence on the species richness of both plants and animals (Ameloot et al. 2005;Cooney et al. 2006;Davies et al. 1997;Grewell 2008;Mellado et al. 2019;Mellado & Zamora 2017;Pennings & Callaway 1996;Press & Phoenix 2005;Shaw et al. 2004;Watson 2001Watson , 2002Watson , 2011Watson , 2015Watson , 2016Watson & Herring 2012). A smaller number of studies nd a broader range of responses in soil microbial communities (Bardgett et al. 2006, Spasojevic & Suding 2011. ...
Article
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We consider the mechanistic basis and functional significance of the pervasive influence of parasitic plants on productivity and diversity, synthesizing recent findings on their responses to drought, heat waves, and fire. Although parasites represent just 1% of all angiosperms, the ecophysiological traits associated with parasitism confer pronounced impacts on their hosts and disproportionate influence upon community structure, composition, and broader ecosystem function. New insights into the roles of their pollinators, seed dispersers, and litter-dependent detritivores have advanced our understanding of how parasitic plants modulate animal communities via their extended and complementary phenology. Direct and indirect impacts of climate change on parasitic plants and their ecological roles are already apparent. Trade-offs between maximizing efficiency at obtaining water from hosts and sensitivity to water stress underlie range shifts and host switching of parasitic plants and increased reliance on these plants by animal communities for food and shelter. Expected final online publication date for the Annual Review of Ecology, Evolution, and Systematics, Volume 53 is November 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... This leads to the speculation that infection with mistletoes may have a positive influence on the ecosystem by improving soil fertility and hence increase the primary production of understory vegetation (Fisher et al. 2013), especially in nutrient-poor environments (Ndagurwa et al. 2014;Spasojevic and Suding 2011). Several studies have shown that soil nutrient concentration varies with host and mistletoe species (Ndagurwa et al. 2014;Watson 2002). Litter quality may also influence the structure and composition of soil decomposer communities of microorganisms, thus resulting in changes in the soil nutrient matrix (Bardgett 2005;Wardle 2002;Watson 2009). ...
... This leads to the speculation that infection with mistletoes may have a positive influence on the ecosystem by improving soil fertility and hence increase the primary production of understory vegetation (Fisher et al. 2013), especially in nutrient-poor environments (Ndagurwa et al. 2014;Spasojevic and Suding 2011). Several studies have shown that soil nutrient concentration varies with host and mistletoe species (Ndagurwa et al. 2014;Watson 2002). Litter quality may also influence the structure and composition of soil decomposer communities of microorganisms, thus resulting in changes in the soil nutrient matrix (Bardgett 2005;Wardle 2002;Watson 2009). ...
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Mistletoes are epiphytic hemiparasitic plants that are known to negatively affect the growth of their hosts, increase tree mortality, and as a consequence change the community dynamics. Mistletoe alters the mineral nutrition of the host and the nutrient cycle in the soil. In the present study, the elemental nutrient status is described for Acacia asak, A. ehrenbergiana, A. gerrardii, and A. tortilis that were infected with the mistletoe Plicosepalus curviflorus, at three levels of infection (no infection, low and high infection). The nutrients of the mistletoe and the soil under the studied acacias were also determined. The elemental contents of the infected Acacia species were significantly reduced compared to non-infected trees, particularly for potassium and sodium. The reduction in the elemental composition was also species-specific and dependent on infection density. Elemental contents of the mistletoe were significantly higher than their Acacia hosts, particularly for nitrogen, phosphorus, and potassium, and the concentrations of minerals in mistletoe tissues were host- and density-dependent. This study revealed a significant increase in nutrients in the soil beneath the canopy of infected Acacia compared to the non-infected trees. Overall, it appears that mistletoe infection has a dual effect. It threatens the health of the Acacia, potentially killing its host tree due to absorption of host nutrients particularly when the infection intense. It also has a positive effect in that it improves the availability of the micro-habitat of nutrients under the canopy, which in turn may contribute to the maintenance of biodiversity.
... Honeyeaters have also diversified extensively across Oceania, where several widespread lineages (Myzomela, Philemon) and about 35 microendemic taxa cover an immense footprint of more than 20 degrees of longitude and 30 degrees of latitude. Arguably, meliphagids are key ecosystem engineers, acting as pollinators, seed dispersers, and plumage mimics and models (Diamond 1982;Watson 2002;Miller et al. 2013;Jønsson et al. 2016). Indeed, by means of their extreme aggression, some species even serve as modifiers of continental-scale avifaunal community structure (Maron et al. 2013;MacNally et al. 2014;O'Loughlin et al. 2015). ...
Article
The honeyeaters are the most species-rich clade of birds east of Wallace's Line. They occupy a wide range of habitats, from desert to rainforest, and occur throughout Australia, New Guinea, and oceanic islands across Wallacea and the Pacific. Honeyeater natural history is well charac-terised, but comparative studies of this group are hampered by the lack of a well-supported phylogeny. Here, we infer the first genome-scale, genus-level phylogeny of the honeyeaters using 4397 ultraconserved elements from 57 species. We analysed the data using concatenated and species-tree approaches, and we found support for novel clades previously undetected in analyses of single-or multi-locus datasets. Despite sequencing thousands of loci, phylogenetic relationships of the New Caledonian Crow Honeyeater (Gymnomyza aubryana) remain equivocal. This study provides a new phylogenetic framework from which to study the ecology and evolution of one of Australasia's most iconic avian clades. ARTICLE HISTORY
... and Stermitz 1997;Schneider and Stermitz 1990;Stermitz et al. 1989). Thus, parasitic plants give rise to new ecological interactions that modify biological communities (Hartley et al. 2015;Pennings and Callaway 1996;Press and Phoenix 2005;Watson 2002) and are thus recognized as keystone species (Watson 2001;Watson and Herring 2012). However, despite the ample information concerning mistletoe effects on host physiology, morphology, and growth patterns, the changes in the host chemical profile while parasitized and the cascading effects of this response on other organisms, remain unclear. ...
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Stress caused by parasitic plants, e.g. mistletoes, alters certain host-plant traits as a response. While several physical implications of the parasite-host relation have been well studied, shifts in the host chemical profile remain poorly understood. Here we compare the chemical profiles of mistletoe (Viscum album subsp. austriacum) leaves and host pine (Pinus nigra subsp. salzmannii) needles and we investigate chemical changes in host needles of trees with different parasite loads (control, low, medium, and high). Our results reveal that despite the intimate contact between mistletoe and host pine, their chemical profiles differed significantly, revealing extremely low concentrations of defense compounds (including a complete lack of terpenes) and high levels of N concentrations in mistletoe leaves. On the other hand, parasitized pines showed unique chemical responses depending on parasite loads. Overall, the content in monoterpenes increased with parasitism. Higher parasitized pines produced higher amounts of defense compounds (phenols and condensed tannins) than less parasitized trees, but amounts in samples of the same year did not significantly differ between parasitized and unparasitized pines. Highly parasitized pines accumulated less N than pines with other parasite loads. The strongest response was found in sesqui- and diterpenes, which were at lower levels in pines under medium and high parasitism. Chemical responses of pines to mistletoe parasitism resembled reactions to other kinds of stress. Low levels induced reactions resembling those against drought stress, while medium and high parasitism elicited responses comparable to those against burning and defoliation.
... Hemiparasitic plants are important contributors to soil nutrient cycles in ecosystems around the world, through litterfall rich in nutrients such as K and P (Quested et al. 2003;March and Watson 2010;Ndagurwa et al. 2014;Scalon et al. 2017). Litterfall from hemiparasitic species has positive effects on community productivity (March and Watson 2007;Spasojevic and Suding 2011;Fisher et al. 2013) and bottom-up effects on diversity (Watson 2002), leading some to describe them as a keystone resource (Watson and Herring 2012). It is concerning that the two hemiparasitic species observed in our study were among the least frequently encountered species. ...
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Nutrient cycling is greatly influenced by dominant plants that contribute high amounts of leaf litter to soils; however, less-dominant and rare species can play keystone roles in nutrient cycling if they have unique nutrient acquisition traits and provide high-quality litter. In many parts of the world, wildfire is likely to become more frequent and intense under a changing climate. The effect this will have on plant rarity and on species with unique nutrient acquisition traits, and thus nutrient cycling, remains poorly understood. Working within an Australian box-ironbark forest, we determined if a relationship existed between species rarity and the uniqueness of their leaf nutrient profiles, and if this relationship changed after prescribed burning. We created an index of species rarity from a data set of woody perennial species abundance in areas before and after autumn or spring burns, or left unburnt. We created indices of uniqueness for the leaf nutrient profiles of 42 woody perennial species occurring in the ecosystem, based on amounts of six macronutrients and four micronutrients found in fresh and senesced leaves of each species. Five nutrient acquisition strategies (mycorrhizal, N-fixing, carnivorous, hemiparasitic and proteoid roots) were represented in the data set. There was no community-wide relationship between rarity and uniqueness of leaf nutrient profiles, and this did not change as a result of fire. However, two hemiparasitic species were relatively rare in the ecosystem studied, and differed greatly from other species due to high K and P in senesced leaves. Thus, some of the rarest species, such as hemiparasites, can be functionally unique. Understanding the functional characteristics of rare species is important so that unique functional contributors can be identified and conserved to prevent local extinction.
... We analysed how nested co-occurrences (that is, where multiple foundation species are found in the same sample) affect inhabitants. Secondary FS were either (1) attached to primary FS (algal filaments attached to freshwater plants by holdfasts; mistletoes penetrating trees with hypocotyls and haustoreums 22,46 ), (2) entangled around primary FS (seaweeds trapped by seagrass blades or mangrove pneumatophores; juvenile mistletoes on tree bark) or (3) embedded within primary FS (shell-forming bivalves growing between salt marsh stems or seagrass leaves 47,48 ). These classes reflect the decreasing structural dependencies, contact intimacies and physical forces required to remove the secondary FS. ...
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It has long been recognized that primary foundation species (FS), such as trees and seagrasses, enhance biodiversity. Among the species facilitated are secondary FS, including mistletoes and epiphytes. Case studies have demonstrated that secondary FS can further modify habitat-associated organisms ('inhabitants'), but their net effects remain unknown. Here we assess how inhabitants, globally, are affected by secondary FS. We extracted and calculated 2,187 abundance and 397 richness Hedges' g effect sizes from 91 and 50 publications, respectively. A weighted meta-analysis revealed that secondary FS significantly enhanced the abundance and richness of inhabitants compared to the primary FS alone. This indirect facilitation arising through sequential habitat formation was consistent across environmental and experimental conditions. Complementary unweighted analyses on log response ratios revealed that the magnitude of these effects was similar to the global average strength of direct facilitation from primary foundation species and greater than the average strength of trophic cascades, a widely recognized type of indirect facilitation arising through sequential consumption. The finding that secondary FS enhance the abundance and richness of inhabitants has important implications for understanding the mechanisms that regulate biodiversity. Integrating secondary FS into conservation practice will improve our ability to protect biodiversity and ecosystem function.
... Increasing the mistletoe load on individual trees will start to show notable effects on the host tree after a few years, as described in figure 2. These can be detrimental for young trees, which due to their small canopy volume seem especially vulnerable to mistletoe infection (Carnegie et al 2009). At this early infection stage initial impacts on biodiversity can be noted, as the mistletoe brooms provide favorable nesting sites and food resources for woodland dependent species (Watson 2002, Cooney and Watson 2005, Barea 2008, Napier et al 2014. ...
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Biotic disturbances are affecting a wide range of tree species in all climates, and their occurrence is contributing to increasing rates of tree mortality globally. Mistletoe is a widespread group of parasitic plants that establishes long-lasting relationships with a diverse range of host tree species. With climate change, ecophysiological stress is increasing, potentially making trees more susceptible to mistletoe infection, which in turn leads to higher forest mortality rates. The perception of mistletoe presence in individual trees and forest stands is divided within the scientific community, leading to an ongoing debate regarding its impacts. Forest managers concerned about stand health and carbon sequestration may view mistletoe as a foe that leads to reduced productivity. In contrast, ecologists may see mistletoe as a friend, in light of the wildlife habitat, biodiversity and nutrient cycling it promotes. However, individual studies typically focus on isolated effects of mistletoe presence within their respective research area and lack a balanced, interdisciplinary perspective of mistletoe disturbance. With this conceptual paper we aim to bring together the positive and negative impacts of mistletoe presence on tree physiology, soil nutrient cycling as well as stand health and stand dynamics. We focus on the role of mistletoe-induced tree mortality in ecosystem succession and biodiversity. In addition, we present potential modifications of mistletoe presence on the energy budget and on forest vulnerability to climate change, which could feed back into stand dynamics and disturbance patterns. Lastly, we will identify the most pressing remaining knowledge gaps and highlight priorities for future research on this widespread agent of biotic disturbance.
... For that rea- son, mistletoe management is commonly related to pest control as it usually involves the removal of mistletoes to avoid damage to trees of commercial importance (Mathiasen et al., 2008). However, mistletoes are more than tree pests, they constitute a key forest resource (Watson, 2001) as they establish complex interactions with other species in different ecosystems across the world ( Shaw et al., 2004;Watson, 2002). Although mistletoes can damage native trees in some extent (e.g., Henr?quez-Vel?squez ...
Article
Mistletoes rely on biotic seed dispersal to ensure their recruitment on appropriate host plants, as their seeds must be deposited on safe sites to allow attachment. As most host-parasite systems, mistletoe's spatial distribution depends on the spatial arrangement of the hosts and on the seed disperser's behavior. We used the mistletoe Tristerix corymbosus, which is solely dispersed by the arboreal marsupial Dromiciops gliroides, and it is capable to parasitize a wide range of hosts. We previously found T. corym-bosus mistletoes to be more abundant and densely aggregated in disturbed habitats, compared to neighboring native forests, at similar levels of disperser abundance and host availability. To explain this pattern, we tested two non-mutually exclusive hypotheses: (1) the larger resource availability in disturbed habitats modify the disperser behavior reducing its home range, and (2) plant species in disturbed habitats are better hosts and offer higher survival probabilities. We sampled 300 mistletoes (98 at the native forest and 202 at the disturbed habitat), which were followed from November 2011 to March 2015 for estimating survival rates and conducting point-pattern analyses. Besides, we tracked ten Dromiciops gliroides individuals using VHF telemetry at both habitats to estimate the home range areas in the two habitats. Mistletoes were aggregated in both habitat types, being stronger at the disturbed habitat with dense plant clumps. Besides, no differences were found on home range of individual D. glir-oides between habitats despite structural and resource availability differences. However, mistletoe survival significantly differed between habitats, as mistletoes had a survival probability of 82.87% at the disturbed habitat, whereas survival probability at the non-disturbed habitat was 53.33%. The most common host species at the non-disturbed habitat is Pluchea absinthioides, a seasonal shrub where mistletoes had a survival probability of 29%. At the disturbed habitat, however, the most common hosts are the shade-intolerant shrubs Aristotelia chilensis and Rhaphithamnus spinosus, which had very low mortality rates. The aggregation pattern found at the disturbed habitat is likely to emerge from differential host mortality rather than behavioral changes on the seed disperser vector.
... Mistletoes are well-known hemiparasitic species that occur throughout the world (Watson 2001 ). They are keystone species in woodlands and forests because they provide high-quality food and nesting or roosting sites for many animals (Watson 2001, 2002, Cooney and Watson 2005, Cooney et al. 2006 ). However, from the phorophyte ' s perspective, mistletoes can be highly detrimental. ...
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Species interactions are susceptible to anthropogenic changes in ecosystems, but this has been poorly investigated in a spatially explicit manner in the case of plant parasitism, such as the omnipresent hemiparasitic mistletoe-host plant interactions. Analyzing such interactions at a large spatial scale may advance our understanding of parasitism patterns over complex landscapes. Combining high-resolution airborne imaging spectroscopy and Li DAR, we studied hemiparasite incidence within and among tree host stands to examine the prevalence and spatial distribution of hemiparasite load in ecosystems. Specifi-cally, we aimed to assess: (1) detection accuracy of mistletoes on their oak hosts; (2) hemiparasitism prevalence within host tree canopies depending on tree height, and (3) spatial variation in hemiparasitism across fragmented woodlands, in a low-diversity mediterranean oak woodland in California, USA. We identifi ed mistletoe infestations with 55-96% accuracy, and detected signifi cant differences in remote-sensed spectra between oak trees with and without mistletoe infestation. We also found that host canopy height had little Influence on infestation degree, whereas landscape-level variation showed consistent, nonrandom patterns: isolated host trees had twice the infestation load than did trees located at the core of forest fragments. Overall, we found that canopy exposure (i.e., lower canopy density or proximity to forest edge) is more important than canopy height for mistletoe infestation, and that by changing landscape structure, parasitic prevalence increased with woodland fragmentation. We conclude that reducing fragmentation in oak woodlands will minimize anthropogenic impact on mistletoe infestation at the landscape level. We argue that advanced remote sensing technology can provide baselines to quantitatively analyze and monitor parasite-host trajectories in light of global environmental change, and that this is a promising approach to be further tested in other temperate and tropical forests.
... Mistletoes are well-known hemiparasitic species that occur throughout the world (Watson 2001 ). They are keystone species in woodlands and forests because they provide high-quality food and nesting or roosting sites for many animals (Watson 2001, 2002, Cooney and Watson 2005, Cooney et al. 2006 ). However, from the phorophyte ' s perspective, mistletoes can be highly detrimental. ...
Article
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Species interactions are susceptible to anthropogenic changes in ecosystems, but this has been poorly investigated in a spatially explicit manner in the case of plant parasitism, such as the omnipresent hemiparasitic mistletoe-host plant interactions. Analyzing such interactions at a large spatial scale may advance our understanding of parasitism patterns over complex landscapes. Combining high-resolution airborne imaging spectroscopy and LiDAR, we studied hemiparasite incidence within and among tree host stands to examine the prevalence and spatial distribution of hemiparasite load in ecosystems. Specifically, we aimed to assess: i) detection accuracy of mistletoes and their oak hosts; ii) hemiparasitism prevalence within host tree canopies depending on tree height, and iii) spatial variation in hemiparasitism across fragmented woodlands, in a low-diversity mediterranean oak woodland in California, USA. We identified mistletoe infestations with 55-96% accuracy, and detected significant differences in remote sensed spectra between oak trees with and without mistletoe infestation. We also found that host canopy height had little influence on infestation degree, whereas landscape-level variation showed consistent, non-random patterns: isolated host trees had twice the infestation load than did trees located at the core of forest fragments. Overall, we found that canopy exposure (i.e. lower canopy density or proximity to forest edge) is more important than canopy height for mistletoe infestation, and that by changing landscape structure, parasitic prevalence increased on specific host locations. We conclude that reducing fragmentation on oak woodlands will minimize anthropogenic impact on mistletoes infestation at the landscape level. Moreover, advanced remote sensing technology can help to quantitatively analyze and monitor parasite-host interactions on oak forests, indicating a promising approach to be further tested on vascular epiphytes over canopies on species-rich tropical forests.
... StructuralGrey et al. 1997; 1998; Major et al. 2001Watson 2001; Watson 2002; Cooney et al. 2006) and are used by Regent Honeyeaters as nesting sites (Oliver et al. 1998). The proportion of total mature trees (>8 m tall) in each transect that were Mugga Ironbarks was included in analyses because previous studies have found strong selection of Mugga Ironbark dominated woodlands by Regent Honeyeaters (Webster and Menkhorst 1992, Oliver et al. 1999). ...
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This is the first Australian study to apply logistical modelling techniques to describe the breeding habitat selection of a widely dispersed, highly mobile, threatened bird species. Landscape and microhabitat structural attributes of breeding habitat occupied by the endangered Regent Honeyeater Anthochaera phrygia in the Bundarra-Barraba region of northern NSW were compared to those of unoccupied habitat using logistic regression modelling. Models containing landscape-scale variables were best at explaining Regent Honeyeater presence. Regent Honeyeater occupation was negatively associated with the amount of woodland cover surrounding a site (1 km and 2 km radius) and distance to patch edge, and was positively associated with site connectivity and linear remnants. Linear, well-connected woodland patches surrounded by cleared grazing land are typical of the remnant native vegetation occupied by Regent Honeyeaters in the Bundarra-Barraba region. The landscape models developed here can be used to identify potential new sites for protection and rehabilitation, and to assess the suitability of unsurveyed or unoccupied sites for the release of captively-bred Regent Honeyeaters, which is identified as one of the priority recovery action for the species.
... Similarly, the litter of the root parasite Bartsia alpina was found to increase the growth (*50 %) of two commonly co-occurring species, Betula nana and Poa alpina (Quested et al. 2003). In addition, the introduction of nutrients along with the patchy occurrence of hemiparasites has potential to increase the spatial heterogeneity of soil nutrients enhancing local plant community richness (Watson 2002;March 2007). Further, this increase in resource patchiness may drive small-scale heterogeneity in productivity and food availability for animals resulting in increased species richness (e.g., birds, Watson and Herring 2012). ...
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Parasitic plants are increasingly becoming the focus of research in many ecosystems. They have been shown to alter litterfall properties and decomposition rates in environments where they occur. Despite this recognition, the role of mistletoes in nutrient cycling in semi-arid savanna remains poorly understood. We investigated the litter input, element returns, and associated below canopy soil nutrient concentrations of three mistletoe species (Erianthemum ngamicum, Plicosepalus kalachariensis, and Viscum verrucosum) that parasitize Acacia karroo trees in a semi-arid savanna, southwest Zimbabwe. Element concentrations in mistletoe leaf litter were enriched relative to the host. Litterfall from mistletoes significantly increased overall litterfall by up to 173 %, with E. ngamicum and P. kalachariensis having greater litterfall than their host trees. Associated with these changes in litterfall was an increase in element returns and the below-canopy soil nutrient concentrations. The increase in nutrient returns was due to both the effect of enriched mistletoe litter and increased volumes of litterfall beneath host trees. Litterfall, element returns, and the below-canopy soil nutrient concentrations were significantly influenced by mistletoe density, with higher values at high mistletoe density. Overall, E. ngamicum and P. kalachariensis had greater influence on litterfall, element returns, and soil nutrient concentrations than V. verrucosum. These findings are consistent with current understanding of enhanced nutrient cycling in the presence of parasitic plants particularly in nutrient-poor ecosystems. We conclude that the introduction of nutrients and associated increase in resource heterogeneity play an important role in determining ecosystem structure and function in semi-arid savannas.
... Mistletoes are a diverse group of aerial parasitic plants occurring in all terrestrial vegetation types (Kuijt 1969), which alter nutrient availability and the structure and composition of plant and animal assemblages (Watson 2001(Watson , 2002(Watson , 2009March andWatson 2007, 2010; Watson and Herring 2012;Ndagurwa et al. 2013Ndagurwa et al. , 2014. They draw up nutrients and water from the host xylem by maintaining higher transpiration rates than their hosts (Ehleringer and Marshall 1995), potentially altering host tree water use. ...
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Aims The below-canopy soil moisture content and litter-layer arthropod abundance and diversity of Acacia karroo trees parasitized by each of three mistletoe species (Erianthemum ngamicum, Plicosepalus kalachariensis, and Viscum verrucosum) and uninfected A. karroo trees were investigated in semi-arid savanna, southwest Zimbabwe. Results The soils below the canopies of mistletoe-infected trees were significantly low in moisture content compared to those beneath uninfected A. karroo trees. Nevertheless, arthropod species diversity was greater by up to 34 % below the canopies of mistletoe-infected trees than beneath uninfected A. karroo trees, with greater abundances beneath trees infected by E. ngamicum and P. kalachariensis. In addition, the majority of the arthropod species associated with mistletoe-infected trees had litter as their dominant foraging substrate. Conclusions Our findings show that mistletoes increase the abundance and diversity of litter-dwelling and –foraging arthropods due to increase in the quality and quantity of litterfall beneath mistletoe-infected trees. By altering the below-canopy arthropod communities and soil moisture content, mistletoes have potential to modify ecosystem processes such as decomposition, soil process rates, and nutrient cycling. Therefore, we suggest that the resulting increase in resource heterogeneity plays an important role in determining the structure and functioning of semi-arid savanna ecosystems.
... It should be noted that shrub cover is only one aspect of structural complexity, which also includes tree density, logs, woody debris and ground cover etc., however many of these habitat variables are intercorrelated. We estimated mistletoe abundance because the availability of mistletoe plants has also been shown as important for many species of woodland birds (Watson 2001(Watson , 2002Bowen et al. 2009). ...
Article
Globally, modification of landscapes for agriculture has had a strong influence on the distribution and abundance of biota. In particular, woodland-dependent birds are under threat across agricultural landscapes in Britain, North America and Australia, with their decline and extirpation attributed to the loss and fragmentation of habitat. Other native species have become over-abundant in response to anthropogenic landscape change and have strong interactive effects on avian assemblage structure. In eastern Australia, the hyper-aggressive noisy miner (Manorina melanocephala) often dominates woodlands in agricultural landscapes through interspecific competition, resulting in declines of species richness of woodland-dependent birds. We aimed to determine the relative influence and importance of interspecific competition, in situ habitat structure and landscape structure for woodland-dependent bird species at the landscape level. We recorded species-specific landscape incidence of woodland-dependent birds in 24 agricultural-woodland mosaics (25 km2) in southern Queensland, Australia. We selected extensively cleared landscapes (10–23 % woodland cover) where fragmentation effects are expected to be greatest. We applied generalised linear models and hierarchical partitioning to quantify the relative importance of the landscape-level incidence of the noisy miner, mistletoe abundance, shrub cover, woodland extent, woodland subdivision and land-use intensity for the incidence of 46 species of woodland birds at the landscape-scale. The landscape-level incidence of the noisy miner was the most important explanatory variable across the assemblage. Both in situ habitat structure and landscape structure were of secondary importance to interspecific aggression, although previous research suggests that the increasing incidence of the noisy miner in fragmented agricultural landscapes is itself a consequence of anthropogenic changes to landscape structure. Species’ responses to fragmentation varied from positive to negative, but complex habitat structure had a consistently positive effect, suggesting in situ restoration of degraded habitats could be a conservation priority. Landscape wide conservation of woodland-dependent bird populations in agricultural landscapes may be more effective if direct management of noisy miner populations is employed, given the strong negative influence of this species on the incidence of woodland-dependent birds among landscapes.
... Parasitic plants in general can strongly affect plant communities because of disproportional effects among potential host species, contributions to nutrient cycling and interactions with other consumers (Watson 2001(Watson , 2002(Watson , 2004Press & Phoenix 2005;Spasojevic & Suding 2011). As consumers, parasitic plants might alter net interactions among plants through preferentially feeding on one of the interacting species (Huntly 1991;Callaway & Pennings 1998). ...
Article
Although there is a large amount of information about the anatomy, physiology and auto ecology of parasitic plants, much less is known about how they affect the interaction among other species and if they present gender preferences when the host is dioecious. The little knowledge available is focused on the effects of parasitic plants on negative plant interactions, but their indirect effects on facilitative interactions remains unexplored. We examined whether the parasitic plant Cuscuta chilensis showed gender preference on its host, the dioecious nurse cushion species Laretia acaulis, and how the presence of the Cuscuta affects relationships between Laretia and its community of beneficiary species.
... Mistletoes are hemi-parasitic plants recognized for their important role in stability and functioning of tropical, temperate and arid systems (Watson 2002, Aukema 2003, Mathiasen et al. 2008. Within these ecosystems, mistletoes often exhibit patterns of clumping (also called aggregation or clustering of multiple mistletoe on a single tree); where compatible host trees (Rödl and Ward 2002) carry multiple infections and neighboring trees harbor significantly fewer numbers of mistletoe (Hoffman et al. 1986, Yan 1990, Lavorel et al. 1999, Reid and Smith 2000, Watson 2009a, b, Carnegie et al. 2009, Rist et al. 2011. ...
Article
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Network theory in ecology has been central to understanding species co-occurrence patterns, specialization and community stability. However, network theory has traditionally focused on the 'higher' trophic level where exploitation of network 'partners' (i.e. individual interactions in response to resource availability) have remained underappreciated. In this study we tested how clumping and host availability influenced mistletoe-host interactions in a semi-arid woodland, central Australia. We used a hierarchical approach that evaluated individual interactions by modifying the traditional randomization technique to simulate clumping and host exploitation. Using published literature we then compared our results with mistletoes from other genera. We found that mistletoes clump on fewer trees than predicted, even though interaction strength was no different from random expectations, and we found no evidence that common trees were heavily infected as predicted by the host availability hypothesis. The rate of host exploitation (measured as the proportion of trees infected) in semi-arid Australia is similar to that for mistletoe genera in other parts of the world. We hypothesize that specific host trees act as a focal point for infection that facilitates the spread and overall population size of mistletoes. Overall our results indicate that resources, such as the number of trees in a mistletoe network, are less important than clumping of individual plants. We suggest that exploitation of available resources may play a similar role in other networks that extend beyond antagonistic relationships such as parasite or herbivore interactions.
... The mistletoebird was a singular exception possibly due to of the occurrence of parasitic mistletoe in all habitat types. Mistletoe is a keystone species with a significantly positive effect on species richness, as it is used by a large number species for food and nesting, disproportionate to their availability (Watson, 2002;Cooney et al., 2006). ...
Article
Eucalypt plantations are expanding rapidly in Australia, and their value for native fauna requires investigation. The relative conservation value of young eucalypt plantations was investigated through assessment of avifauna richness, abundance and composition using transect surveys incorporating point counts in five broad habitat types—dryland forests, riparian forests, dryland plantations, riparian plantations, and riparian pastures (strips of riparian vegetation surrounded by pastures). A total of 73 species were recorded during formal surveys. Species richness and abundance were comparable among all habitat types except dryland plantations, which supported fewer species and in lower numbers. The avifauna assemblage differed according to broad habitat types. Forest habitats (dryland and riparian) harboured more forest- and woodland-dependent species, and a greater abundance of nectarivores and insectivores. Riparian plantations supported a similar number of forest- and woodland-dependent species to forest habitats, but also retained some open-country species. Riparian pastures had the highest cumulative species richness, reflecting a diverse mix of forest- and woodland-dependent birds and open-country species. It was the preferred habitat type for granivores and vertebrate eaters. Dryland plantations were dominated by common species and omnivores, and supported fewer forest- and woodland-dependent birds, insectivores and frugivores compared with other habitat types. The presence of riparian strips increased avifauna diversity and abundance in plantations and pastures to a greater extent than predicted by the proportional area of riparian habitat. The importance of riparian habitats needs to be recognised and incorporated into management policies if biodiversity conservation is to be an objective of plantation establishment.
... For example, the loss of top predators may lead to an increase in herbivores and loss of plant diversity and environmental degradation though overgrazing. Watson (2001) contends that mistletoes are keystone species in Australian woodlands because they provide an array of resources for many other species (e.g., nectar, fruit, foliage, nest sites), and ha s shown that woodlands without mistletoes may have lower bird diversity (Watson 2002). Ecosystem engineer s, species that directly modulate the availability of resources to other species by causing physical state changes in biotic or abiotic materials (Law ton 1994), are a special case of keystone species. ...
... Moreover, Amyema represents an important food source for many animals-both directly in terms of nectar, fruit and leaves, and also indirectly as a foraging substrate for insectivorous birds. These interactions have been found to have an effect on the distribution patterns of particular species (Thompson and Owen 1964;Oliver et al. 2003) and diversity patterns of birds generally (Watson 2002). Although fragmentary, these findings are remarkably congruent with research on Arceuthobium-wildlife interactions, highlighting the analogous roles they play in their respective systems. ...
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Whereas the biology, physiology and systematics of mistletoes have been explored in considerable detail, their ecology has received less attention and our understanding is highly fragmentary. A conspicuous exception is the dwarf mistletoes (Arceuthobium spp.)—a genus that exclusively parasitises coniferous trees, including many commercially valuable species in the forests of the western United States. Accordingly, these plants have been the subjects of intensive cross-disciplinary research for the past five decades, initially from a control and management perspective but extending into most aspects of their ecology and life history. This review summarises our understanding of dwarf mistletoes, focusing on recent developments in the areas of mistletoe-wildlife interactions, fire, ecosystem ecology and conservation biology. We also compare dwarf mistletoes with Australian mistletoes in the genus Amyema, a diverse suite of species found throughout the continent. Despite fundamental differences in their evolutionary origin and most aspects of their autecology and life history, the genera exhibit many similarities in terms of their ecological role in forests and woodlands, and their influence on stand- and forest-scale dynamics. In particular, both groups provide nesting resources for a range of birds and mammals, and nutritional resources for a diverse assemblage of species. Both also interact with fire, potentially leading to changes in successional dynamics at the stand scale. At an applied level, both groups are widely considered as pests but, as our understanding of these keystone species improves, they have the potential to serve as sensitive ecological indicators for their respective ecosystems. Key research priorities are identified for further research on both groups of mistletoes and more explicit comparative research, with Arceuthobium serving as a valuable template for future work on Amyema and Australian mistletoes in general.
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Part A2 : Surrogate measures to assess environmental and silvicultural outcomes of the NSW private native forestry (PNF) Code of Practice
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Mistletoe proliferation has contributed to eucalypt decline in rural lands in south-eastern Australia, but has seldom been recorded within forests. We report here on mistletoes increasing deep inside extensive eucalypt forest near Eden. Mistletoes (chiefly Amyema pendula (Sieber ex Spreng.) Tiegh., some Muellerina eucalyptoides (DC.) Barlow) were counted in 180 plots in various logging and burning treatments within a long-term experimental area. In 141.4ha, there were 516 mistletoes in 1990-1991, and 1478 mistletoes in 2004-2006. The number of trees with mistletoes increased (doubling in logged coupes and almost tripling in unlogged coupes), and the number of mistletoes per tree increased (by ∼30%). However, mistletoe prevalence remained low in 2004-2006 (2.7% of trees in logged coupes and 3.7% in unlogged coupes). Intensive logging limited the increase in mistletoe-bearing trees, probably because there were fewer trees available in logged coupes, but had no significant effect on the increase in mistletoes per tree. Low-intensity prescribed burns had no significant effect on mistletoe numbers, even with a high frequency of burning, probably because of their low scorch heights. We suggest that the observed increase in mistletoes in this forest, rather than indicating an ecological imbalance, is part of a natural cycle of boom and bust, with populations crashing in severe wildfires.
Chapter
Mistletoes are a polyphyletic group of approximately 1,400 species of obligate hemiparasites, distributed worldwide. While they obtain all of their minerals and water from their host (typically a tree or shrub), they are green plants that generally manufacture their own carbohydrates by photosynthesis. They maintain low water potentials relative to their hosts by concentrating soluble cations and organic compounds in their tissues, and typically have higher rates of transpiration than their hosts. They are pollinated primarily by birds, and birds are also the main vector for fruit dispersal. In addition to these mutualistic interactions, mistletoe is a popular food source for a wide variety of animals, often providing nutritional resources when little else is available. They are also highly favored roost and nest sites for a wide range of animals and are considered one of the main causes of hollow formation in many regions. Mistletoe can therefore be considered a keystone resource, having a disproportionate influence on the ecosystem as a whole, affecting distribution patterns of organisms both directly and indirectly. While some mistletoe species can have deleterious effects on their host, most mistletoes are best regarded as water-parasites, having a negligible effect on host survivorship. Given the range of interactions mistletoes have with pollinators, dispersers, herbivores, and hosts, they are a sensitive assay of environmental integrity and have been used as indicators of overall habitat health.
Chapter
Mistletoes are a functional category of plants, defined as shrubby, aerial hemiparasites which depend on their host plants for water and mineral nutrition. Although three aberrant species (all in monotypic genera) are root parasitic, mistletoes are stem parasites, attaching to their hosts via specialized organs called haustoria. Mistletoes belong to the order Santalales and are arranged in the families Loranthaceae, Viscaceae, Misodendraceae, and Santalaceae, with the great majority of species belonging to the first two families (Nickrent et al. 2010). Although some species regularly parasitize lianas and other mistletoes, most species are dependent on trees and shrubs as principal hosts. The more than 1,500 species worldwide live in diverse habitats from rainforest to semiarid woodlands and are absent only from habitats devoid of woody hosts (e.g., polar, alpine and desert environments). Mistletoes are an important food source and nesting site for many birds and mammals (Watson 2001; Cooney et al. 2006; Mathiasen et al. 2008) and have a positive effect on the diversity and distribution of vertebrate animals in a range of habitats (Mathiasen et al. 2008; Watson 2002). By comparison, the ecological interactions between mistletoes and invertebrates—particularly arthropods—are poorly known. Unlike birds and mammals—long-lived and highly mobile animals that visit mistletoes periodically—many insects live their entire lives within mistletoe clumps, completely dependent on them for food and shelter. In this contribution, we summarize recent research on mistletoe-dependent arthropods, contrasting the extreme specialism exhibited by herbivorous groups, with lower substrate specificity (and greater dependence on structural complexity) displayed by predatory taxa. Rather than simply a subset of the biota found in the host canopy, we demonstrate that arthropods in mistletoes represent discrete and complementary assemblages, hitherto overlooked islands within a sea of forest and woodland treetops. Finally, we consider these findings in terms of the threats facing many forested systems, demonstrating the utility of mistletoe-dependent arthropods as sensitive indicators of overall forest health and ecosystem integrity.
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A regional survey of 253 forest sites on the southwestern slopes and adjacent highlands of New South Wales recorded a total of 530 animals from five species of nocturnal forest birds and nine species of arboreal marsupials. One additional species, the Squirrel Glider Petaurus norfolcensis, was trapped during supplementary searches. Elevation (climate) and forest type were the major factors accounting for the distribution of this fauna. Minor environmental gradients included geology, the density of hollow-bearing trees, topography, logging intensity and fire. The patterns of landuse in the region contributed to interactions between elevation, forest type and management history (logging, fire and grazing) which restricted inferences about the habitat requirements of animals. Forest types occurring at either end of the elevational (wet-dry) gradient (Alpine Ash and Box-Stringybark) were poorer in species than forests occurring at intermediate elevations (Alpine Gums, Wet Peppermint and Dry Peppermint). The Wet Peppermint forest type, which was the richest in species of nocturnal animals, has been deliberately selected in the past for conversion to pine plantations. The fauna of the region was generally more sparse and patchy compared to four other regions (northeastern and southeastern New South Wales, and northeastern and Central Highlands of Victoria) where similar studies have been undertaken. Numbers of large forest owls and the Greater Glider Petauroides volans were recorded less commonly than expected and may have declined in the region. The Common Brushtail Possum Trichosurus vulpecula was particularly abundant. This species and the Common Ringtail Possum Pseudocheirus peregrinus appeared to maintain their numbers in small (<2 000 ha), isolated forest fragments.
Article
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Remnant ecosystems in agricultural landscapes are poorly understood in terms of their diversity, function and dynamics under altered disturbance regimes, and of how these influence resilience to future disturbance. Understanding native ecosystem responses to novel and multiple disturbances is a crucial foundation for adaptive management to maintain and enhance biodiversity and critical ecosystem services in production landscapes. This is particularly significant where environmental change drives irreversible threshold responses and ecosystem transitions to less functional, or less preferred, alternative ecological states. This research was conducted in remnant riparian woodland ecosystems along a regulated section of the Condamine River, southern Queensland, an ephemeral dryland river system draining an intensively farmed landscape in eastern Australia. Riparian woodland remnants on the Upper Condamine floodplain are subject to significant changes in hydrological regimes and land use intensity. They also exhibit dieback and limited recruitment of canopy species, as well as widespread invasion by the introduced perennial herb Phyla canescens (lippia); however, efforts to address these issues have largely failed to curb ongoing degradation, potentially due to a lack of understanding of the key drivers of ecological change operating in this complex socio-ecological landscape. This research addressed questions about the drivers of floristic composition, functional diversity and woodland condition in fragmented riparian woodland communities associated with a regulated dryland river system, and embedded in a production landscape. In particular, it investigated ecological responses to the range of disturbances (including altered hydrology, land use intensity, resource availability, and key species interactions) prevalent in this highly modified landscape. Two of the four studies presented test the hypothesis that the composition and condition of riparian woodland remnants on the Upper Condamine floodplain are associated with current levels of longitudinal and lateral hydrological connectivity. These studies used a stratified sampling design which partitioned the study area into river sections, and also considered the influence of lateral overbank and overland flood flows, and grazing within ecosystem fragments (remnants). Full floristic sampling and condition assessments of mature Eucalyptus camaldulensis/E. tereticornis trees were conducted at a total of 24 sites in 2004/05. Significant patterns in floristic composition, functional diversity and woodland condition were explained by differences in hydrological variability; however, the confounding influence of land use and interaction between within-remnant land use (specifically grazing) and hydrological factors for some measures, indicated response to a complexity of drivers. A third study investigated the influence of local and landscape-scale hydrological and land use variables. It used a Bayesian model averaging (BMA) approach to identify informative model sets of explanatory variables, and key environmental predictors of floristic composition, community structure and ecological condition. A novel method was developed to examine dynamic transitions in species richness and abundance between reciprocal pairs of functional groups; this method used the ratio of species richness (or total abundance) in corresponding pairs of functional trait groups (e.g. C3:C4 species) as a community response variable reflecting the relative importance of each group along the environmental gradients tested. Groundwater decline was the primary predictor of ecosystem response, with lower floristic and functional diversity and more severe dieback associated with increasing depth to groundwater; this result suggests an overarching reliance on shallow groundwater resources for maintenance of ecosystem resilience not previously reported for this ecosystem type in Australia. Lippia abundance and dominant tree condition were also important biotic drivers of ecosystem condition in these communities, and key predictors of floristic composition and functional group richness and abundance transitions. Poor tree condition and loss of hydraulic function was associated with secondary impacts on less well adapted ‘terrestrial’ groundcover species, while the subdominant species Acacia stenophylla responded positively to competitive release due to poor tree function and reduced tree density. Lippia cover was also strongly associated with the density (positively) and mortality (negatively) of mature trees. Small scale species interactions were investigated in a study which tested differences in groundcover vegetation composition and lippia cover, reproductive condition and growth habit between ‘distance from tree’ and topographic position treatments in a riparian woodland on the Upper Condamine floodplain. Sampling was conducted along twelve transects extending from the base of mature Eucalyptus camaldulensis/E. tereticornis trees into canopy gaps. Results indicated that scattered trees play a significant role in facilitating the abundance and condition of lippia in this landscape, with evidence of high lippia abundance, reproductive effort and consolidated clonal growth under trees canopies (described as a ‘halo’ effect). This interaction is likely to play a significant role in the persistence of this mesic, though highly adaptive, species in this drought prone landscape. Lippia cover greater than approximately 20% was also found to have a significant impact on the abundance and diversity of non-lippia species in these grassy woodlands. Results of this research are synthesised in a conceptual resilience-based state and transition ‘riparian woodland response’ model identifying three critical transitions for riparian ecosystem condition and function related to effectively irreversible changes in the landscape: (i) transformation to a lippia-invaded landscape with the introduction, establishment and spread of lippia on the floodplain; (ii) transformation from riparian communities which are well buffered against drought, due to connection with shallow groundwater, to communities reliant on and susceptible to stochastic climatic variability; and (iii) population failure in the dominant functional canopy species complex, Eucalyptus camaldulensis/E. tereticornis, and transformation to non-eucalypt-dominant floodplain ecosystem types such as Acacia stenophylla-dominant woodlands, floodplain grasslands or lippia-dominant herblands with significantly reduced capacity to provide essential ecosystems services in riparian contexts. In conclusion, this research indicates that observed condition in riparian woodlands on the Upper Condamine floodplain is an integrated response to a range of disturbances, but that certain changes (in particular, groundwater decline due to overextraction in combination with extended drought) may be critical to the long-term persistence and function of these remnants. This study indicates the importance of systems-based empirical research to developing better understanding of the function and dynamics of remnant ecosystems in highly modified landscapes subject to both natural and anthropogenic disturbance regimes. The resilience-based approach also focuses attention on the key drivers of stability and critical transitions in these complex socio-ecological systems. Such research is vital to evaluating and predicting changes in remnant native ecosystems and the provision of important ecosystem services, and as a basis for adaptive management in multi-use production landscapes.
Article
Worldwide, mistletoes act as a keystone resource, providing food (nectar, fruit and foliage) and structural (nesting sites) resources to hundreds of fauna species. In Australia, loranthaceous mistletoes depend on birds for pollination and dispersal, and provide important nectar and fruit resources to a large number of nectarivorous and frugivorous species of bird. We investigated whether avian species richness and community structure varies with flowering and fruiting of two common mistletoe species (Loranthaceae : Wireleaf Mistletoe, Amyema preissii; and Box Mistletoe, A. miquelii), conducting monthly surveys of both birds and mistletoes over 1 year at five sites in south-western Western Australia (WA). Flowering and fruiting periods were distinct and differed both among sites and between mistletoe species. Nectar and ripe fruit were available for up to 5 months (Box Mistletoe) or 6-7 months (Wireleaf Mistletoe) at individual sites, but were available every month of the year across all sites. The presence of fruiting, but not flowering, mistletoe was associated with changes in bird community structure. Mistletoebirds (Dicaeum hirundinaceum) were significantly more likely to be recorded during months when ripe mistletoe fruit was present and the overall bird species richness was higher for these survey months. Mistletoes provide important resources, but further investigation is required to assess whether they act as a keystone resource in south-western WA.
Article
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Ecology is the study of interactions that determine the distribution and abundance of organisms and its main goal is to discover widely applicable, general principles in nature [[1][1]]. Ecology therefore integrates traditional disciplines like zoology and botany, and terrestrial, marine and
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This study investigated the effects of mistletoe infection on N cycling in a semi–arid savanna, south-west Zimbabwe. We established five plots (10 × 10 m) which each included three large canopy-dominant Acacia karroo trees infected by one of three mistletoes (Erianthemum ngamicum, Plicosepalus kalachariensis and Viscum verrucosum) and non-infected A. karroo trees. In each plot, we measured litterfall, litter quality (N, phenolics, tannins and lignin), soil nutrient concentrations and N transformations beneath tree canopies. Soil N, P and Ca were greatest beneath trees infected by P. kalachariensis than beneath non-infected trees. Litterfall and litter N returns were 1.5, 2 and 1.4 times more beneath A. karroo trees infected by E. ngamicum, P. kalachariensis and V. verrucosum, respectively. Mineral N increased with mistletoe infection but did not exceed 20%. Soil N transformations were greater beneath trees infected by E. ngamicum (> 40%), and lower beneath trees infected by P. kalachariensis (<50%) and V. verrucosum (<48%) than beneath non-infected A. karroo trees. Soil N transformations were negatively correlated with condensed tannins, lignin and lignin : N. We conclude that the improved N concentration can increase resource heterogeneity, which may alter the ecosystem structure and functioning in the semi-arid savanna.
Article
Increases in populations of mistletoes were observed in undisturbed eucalypt forest near Eden, New South Wales. Repeated counts in an ecological research area showed that there were large increases in mistletoes over 13 years. Populations of mistletoes quadrupled in areas that had few or no prescribed burns. Mistletoes doubled in areas that were patchily burnt by fires of generally low intensity six times in 13 years, but this increase was not statistically significant. Hypotheses advanced to explain the perceived proliferation of mistletoes in rural lands cannot account for the increases in undisturbed forests. However, the results of this study are consistent with a general hypothesis of tree decline in rural lands and forests caused by chronic abiotic stress. Unnatural exclusion of low intensity fire may impair the health of eucalypt forests and cause outbreaks of pests, pathogens and parasites. Populations of mistletoes or other parasites could readily be monitored as indicators of ecological imbalance.
Article
Interactions between birds and mistletoes have been described in many regions worldwide, with most research focusing exclusively on the role of birds as seed and pollen vectors for these hemiparasitic plants. Mistletoe is also widely used by birds as a nesting site, with a recent family-level compilation identifying species in 43 families worldwide nesting in mistletoes. We reviewed breeding and nesting accounts of Australian birds to explore the extent of mistletoe nesting at the species level within an entire avifauna. In total, 217 species of Australian arboreal nesting bird from 29 families are here reported nesting in mistletoes, representing 66% of Australian species that nest in the foliage of trees. A further 28 species are also known to nest in mistletoes incidentally. This increases the total number of avian families known to exhibit this behaviour worldwide to 60, across 16 orders. Although no species can be considered an obligate mistletoe nester, several families regularly nest in mistletoes with >90% of Australian species known to have nested in mistletoes, including Pomatostomidae, Artamidae, Corvidae and Ptilonorhynchidae. Determining preference for mistletoe nesting is a priority for understanding this behaviour and we present guidelines for evaluating whether a particular species preferentially uses mistletoe as a nest-site. We postulate that the evergreen, dense habit of mistletoes provide a strong structural substrate on which to build a nest, offering a higher level of concealment and a more moderate nest microclimate than otherwise similar arboreal nest-sites. These features may also have a role in reducing nest predation and enhancing survivorship of nestlings. Future studies should focus on the mechanisms underlying this pattern using field experiments to evaluate the influence of mistletoe on nest microclimate, rates of predation and nest success.
Article
Parasitic plants are less affected by resource constraints than other plants and most exhibit broad host tolerances, occupy large distributional ranges, and produce high numbers of propagules. Yet, parasitic plants are characteristically rare in undisturbed habitats, and patterns of distribution within host populations are often highly nonuniform. Previous work on root and shoot parasites has identified strict germination requirements for many species but, while explaining host ranges and site-microsite preferences for particular species, this cannot account for the highly clumped spatial structure of many parasitic plant populations. Other research has examined the role of seed vectors, but in most systems studied, dispersers are not limiting and their dietary breadth, substrate use, habitat preferences, and distributional ranges exceed the extent of the parasitic plant. Here, I propose the "host-quality hypothesis," suggesting that variation in the quality of potential hosts can account for nonrandom occurrence patterns of parasitic plants in many systems. "Quality" can relate to access to water, nutrients, or other resources that are generally limiting to hosts, whereby parasites are more likely to establish and survive on hosts with greater access (i.e., higher quality from the parasite's perspective). Rather than supplanting germination requirements operating at the individual host plant scale or disperser behaviour operating at the landscape scale, this resource-based hypothesis applies at stand and population scales, explaining why some individuals within a stand or population are infected, while other apparently similar hosts are not susceptible. This hypothesis is explored using case studies on root and shoot hemiparasites. and is consistent with a diverse array of findings from a range of temperate and and systems.
Thesis
Human domination of the planet is driving species extinct. Each species has not only intrinsic value, but ecological functions of organisms are also essential for the integrity of ecosystems that allow people to benefit from key ecosystem services. In order to retain global biodiversity, we must study the factors behind species' declines, understand their consequences, improve biodiversity capacity of human-dominated landscapes, and persuade human communities to preserve their natural heritage. I address these issues by modeling bird extinctions in the 21st century, investigating effects of habitat degradation on tropical forest birds, and reviewing birdwatching tourism. Analyzing a database of all bird species, I found that certain groups, such as frugivores, piscivores and scavengers, are more extinction-prone than average, and oceanic islands and forested landscapes have more threatened species than average. These patterns are likely to deteriorate in the 21st century, signaling the potential loss of crucial ecosystem services such as pest control, pollination, and seed dispersal. In Uganda, I found that past forestry practices had long-term negative impacts on forest birds, whereas low intensity forestry was compatible with the preservation of local biodiversity. In Costa Rica, I showed that understory insectivorous birds disappeared from forest fragments not due to lack of food, but because of limited mobility. Three forest bird species that persisted in agricultural countryside did so either by being pre-adapted to disturbed habitats ( Catharus aurantiirostris ) or by being mobile and making efficient use of 11% of the landscape still covered by trees ( Tangara icterocephala and Turdus assimilis ). Radio telemetry underlined the importance of remnant trees, riparian strips, and small forest patches for native forest species. Analysis of birdwatching tourism revealed that, just as human-dominated landscapes are often excluded from conservation initiatives, most local people in less-developed areas are also excluded from income generated by birdwatching that is overwhelmingly conducted by wealthy citizens of developed countries. If the combination of large scale habitat clearance, exclusion of human-dominated landscapes from conservation policies, and alienation of local communities from ecotourism initiatives continues, consequent disappearance of species is likely to cause collapses in ecosystems and their services that are crucial for humanity.
Chapter
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Overview: Birds’ ecological functions cover a wide spectrum, from creating soil to shaping primate behavior, and many species play key ecological roles, such as decomposition, predation, pollination, nutrient deposition, and seed dispersal. From an ecosystem functional perspective, birds are mobile links that are crucial for maintaining ecosystem function, memory, and resilience. The three main types of mobile links, genetic, process, and resource linkers, encompass all major avian ecosystem services. Rapid losses of tropical bird species may cause substantial reductions in certain ecosystem processes before we have time to study and understand the underlying mechanisms.
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Conservation of Tropical Birds has been written by four conservation biologists whose expertise spans all the tropical regions of the world. It is the first book to cover all the major issues in tropical bird conservation. Current problems faced by tropical bird conservationists are summarised and potential solutions outlined based on the results of case studies. Birds are key indicators of ecosystem health, and such a well-studied group of organisms, that they provide an excellent lens through which to examine global conservation problems caused by phenomena such as climate change, declines in ecosystem services, habitat loss, fires, overexploitation, and invasive species. Therefore, the book also provides an engaging synopsis of the general issues in conservation and the problems faced by other wildlife. This book serves as an important resource and companion to all people interested in observing and conserving birds in the tropics and elsewhere. © 2011 Navjot S. Sodhi, Cagan H. Sekercioglu, Jos Barlow, Scott K. Robinson.
Article
Parasitic plants, such as mistletoes, are important components of tree canopies, providing food and shelter for a range of vertebrates and invertebrates. Arthropods from several orders are known to inhabit mistletoes but no direct comparisons between these plants and their host plants have been conducted until present. In this study, the composition and abundance of arthropods occurring on hemi-parasitic box mistletoe, Amyema miquelii ((Lehm. ex Miq.) Tiegh., Loranthaceae), on Eucalyptus (L., Myrtaceae) trees from the south-west slopes region of eastern Australia were investigated. Here a comparison of the arthropod assemblages at the ordinal level is presented. Specimens of Insecta and Arachnida were sampled from box mistletoe and three of its most common host species, using restricted canopy fogging, in two consecutive years, in nine remnants of grassy-box woodlands. The same 10 arthropod orders were sampled from the mistletoes and their eucalypt hosts but the total density of arthropods was greater on the eucalypt foliage. The latter result might be attributed to the significantly greater nitrogen content of the eucalypt foliage than the mistletoe foliage. One year after de-faunation, all but one of the arthropod orders had re-colonised the mistletoe plants. The total abundance of arthropods (particularly Hemiptera and Hymenoptera) on the mistletoes was greater in the second year of sampling, in which drought conditions occurred. Future research of arthropod assemblages in tree canopies should be more inclusive of the full range of substrates or habitats within canopies. Furthermore, investigation of the nutritional quality of mistletoe foliage compared with their host trees is required for a better understanding of the factors driving variation in community composition of arthropod assemblages.
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We analysed distribution records of mistletoes (Loranthaceae and Viscaceae) in South Africa in terms of host taxa and geographic patterns. Few species are found in nutrient-poor Cape shrublands (fynbos) and in the southern evergreen forests on nutrient-poor sands. The most species-rich areas are the nutrient-rich mesic savannas (including Valley Bushveld, a subset of savanna). Mistletoe species richness is significantly correlated with the average nitrogen levels of the woody plants in any biome, suggesting that the overall nutrient status of a biome influences mistletoes species richness. The analysis of host-choice of mistletoes also indicates a non-random distribution; thirty-three genera in twenty-two plant families host from three to twenty-four different mistletoe species, suggesting that parasitism is not related to phylogenetic position. The most important host genera are Acacia (hosting twenty-four spp. mistletoes), followed by Combretum (fourteen), Maytenus (thirteen) and Rhus (twelve). The species richness of mistletoes on host genera is significantly correlated with mean host N, and in four of five areas sampled, the number of mistletoes on host trees was significantly correlated with host N.
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Ten major forest types were distinguished in the Bega-Bermagui region on the south coast of New South Wales: Acmena rainforest, coastal Banksia-Eucalyptus scrub, five types of mature Eucalyptus forest, and three types of forest regenerating after intensive logging. A total of 123 bird species were recorded in these forests between 1977 and 1983. The bird communities of the rainforest and the coastal scrub were the most distinctive in that a number of species that were common in eucalypt forest were absent or rare. Among the various types of mature and regenerating eucalypt forest the major differences in birds were between the dry forests of the ridges and the moist forests of the gullies. Forest types with winter-flowering Eucalyptus or Banksia species attracted many honeyeaters and lorikeets at that season. In eucalypt forest 0 - 4 years after intensive logging many bird species were less frequent than in mature forest and few species were found breeding. There was no appreciable colonization of these logged areas (which were only 10 - 20 ha in size) by non-forest birds. In eucalypt forest 9 - 17 years after intensive logging the bird community more closely resembled that of mature forest.
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Red Wattlebird Anthochaera carunculata (n = 97) and Noisy Friarbird Philemon corniculatus (n = 229) nests were monitored over eight breeding seasons in eucalypt woodland in northern New South Wales. Red Wattle-birds nested in Eucalyptus viminalis and E. bridgesiana more frequently than expected from their relative abundance at the site. Noisy Friarbirds avoided stringybarks (E. caliginosa) but selected other eucalypts disproportionately. Nest success was similar in the two species (33% in Red Wattle-birds and 38% in Noisy Friarbirds), despite Friarbird nests being placed further horizontally from the base of the nest tree and being more conspicuous. The similar success may be because Noisy Friarbird nests are more inaccessible to mammalian predators and Red Wattlebird nests are less conspicuous to avian predators. In addition, Noisy Friarbirds tend to be more aggressive to avian predators than Red Wattlebirds, which may allow them to benefit from nests that have a good view of their surroundings. Neither species showed a relationship between nest success and nest height, horizontal distance from the base of the tree, nest tree height and trunk diameter or nest conspicuousness. Noisy Friarbird nests in E. blakelyi, although chosen most frequently, were less successful than those in other tree species and nests around mean height were less often successful than those higher or lower. The difference in nest locations between the species and diversity of nest sites chosen within each species could reduce the chance of a nest predator developing search images for specific nest locations. The suggestion that Noisy Friarbird nests in less common locations are more likely to be successful supports this hypothesis. Nests at the edge of the habitat patch and near tracks used by humans did not differ in their success rate from nests in the centre of the patch or away from tracks.
Article
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The damaging effects of mistletoes Amyema spp. on host eucalypts in rural Australia concern many landholders, but few data are available to evaluate mistletoe impacts or formulate management strategies. We used an experimental disinfection approach to determine the effects of a putative pest mistletoe, Amyema miquelii, on its two principal hosts, Blakely's red gum (Eucalyptus blakelyi) and yellow box (Eucalyptus melliodora), on pastoral properties in northern New South Wales. For each host species, pairs of nearby trees were matched for heigth, diameter at breast height, level of mistletoe infestation and distance to neighbouring trees. One tree per pair was chosen at random and all the mistletoes pruned. After 33 months all treated trees were still alive, but among control trees seven of 29 red gums and one of 20 yellow box trees had died. The difference in survival between treated and control trees was significant for red gum. Among surviving pairs of trees, treated trees of both species had significantly greater diameter increments and significantly more foliage than untreated trees. After 33 months, the average increase in relative host foliage biomass attributable to removal of mistletoes was 22% in red gum and 24% in yellow box, compared with untreated controls. The average increase in radial growth attributable to mistletoe removal was 55% in red gum and 49% in yellow box. Diameter increment was negatively and linearly related to mistletoe infestation level in control trees of both species. The differences between infected and disinfected trees in this experiment may underestimate the impact of Amyema miquelii on host growth because small amounts of host biomass were unavoidably lost during disinfection. In a separate experiment, loss of host biomass had a significant negative impact on diameter increment. Although the results indicate that control of serious Amyema miquelii infestation of individual trees will be worthwhile in terms of immediate host survival and higher growth rate, prudent long-term management may well allow for the loss of small numbers of farm trees to mistletoes when planning tree recruitment and utilisation.
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Thesis (M.S.)--Colorado State University, 1991. Includes bibliographical references.
Book
This book lists the stomach contents of Australian songbirds collected by the CSIRO Wildlife and Ecology from 1963 to 1980.
Book
This book lists the stomach contents of Australian non-passerine birds collected by the CSIRO Wildlife and Ecology from 1963 to 1980.
Article
Buloke Allocasuarina luehmanni woodland is an endangered habitat type that was once widespread in southern Australia but now is restricted to a series of remnants, many of which are located in the Wimmera region of western Victoria. The bird communities inhabiting 27 remnants were sampled on transects of 1.0 ha at 6-week intervals over one year. Ninety-five species of birds were observed in Buloke woodlands, of which 66 species were recorded during transect counts. The total species richness, the richness of groups of birds based on their habitat use, and the composition of assemblages on transects, were examined in a series of analyses with respect to habitat type (which probably reflects 'quality'), remnant area, shape, isolation and geographic location. There was little evidence for attributes of remnants significantly influencing species richness per transect, but the composition of avifaunal assemblages varied in relation to habitat type, size and geographic location. The Buloke woodlands supported a diverse assemblage, including numerous species believed to be experiencing a regional decline in southern Australia. The composition of the Buloke assemblage has similarities to those of dry eucalypt woodlands across the plains of central Victoria, but elements contributing to a distinctive avifauna include species associated with semi-arid and mallee environments, and a high frequency of occurrence of a group of small insectivores (thornbills, robins) that favour dry She-oak and Callitris woodlands. A likely reason for the rich representation of small insectivores in woodland stands, even in small degraded remnants grazed by stock, was the scarcity of the Noisy Miner Manorina melanocephala that are often common in eucalypt remnants and known to aggressively exclude other species. The results of this study add weight to the recommendation that protection and restoration of Buloke woodlands is a priority for conservation in the Wimmera bioregion of Victoria.
Article
The incidence of mistletoe plants on eucalypt trees in dry sclerophyll forest was recorded in Eden Forestry Region, New South Wales. Before logging there were 210 trees per hectare over 10 cms diameter breast height. On average 2.8 trees per hectare carried mistletoe at the rate of 5.0 mistletoe plants per hectare. In similar forest logged to 91 trees per hectare there remained 1.8 trees per ha carrying 2.3 mistletoe plants per ha. Yertchuk, Eucalyptus consideniana, Maiden, was the most common tree and had the most mistletoe plants in the study area with an average of 1.7 plants per tree. Birds foraging in mistletoe flowers were compared with birds foraging in eucalypt blossom to determine the use of these resources. Out of 180 plots 41 individuals were recorded as foraging in mistletoe while only eleven birds were recorded feeding amongst blossom of Eucalyptus sieberi L. Johnson. Logging reduced the number of trees per ha and therefore of mistletoe plants per ha and the number of bird foraging activity in approximately the same proportion. Birds acknowledged as common to abundant were involved in this foraging data.
Article
Dwarf mistletoes (Arceuthobium spp.) are parasitic plants that are widely distributed in coniferous forests of the northern hemisphere. Because the effects of dwarf mistletoes on their host trees include stunted growth, reduced seed production, and death, these mistletoes may have a substantial influence on forest structure. Studies of the effects of dwarf mistletoe on forest communities have focused primarily on their influence on timber production. We studied the effects of southwestern ponderosa pine dwarf mistletoe (A. vaginatum) on the abundance and diversity of bird communities in central Colorado. Four stands, which ranged in level of mistletoe infestation from none to heavy, were selected at each of two locations. Each stand was surveyed approximately once per week during the avian breeding seasons of 1989 and 1990 by spot mapping. The number of bird registrations and bird species richness were positively correlated with the level of dwarf mistletoe, and this pattern was consistent among 24 of 28 avian species. No species had a significant negative correlation with the level of dwarf mistletoe. The relative abundance of bird species (i.e., evenness) did not differ among stands. The number of cavity-nesting birds detected also was positively correlated with both dwarf-mistletoe levels and number of snags. The number of snags and dwarf-mistletoe levels also were highly correlated. Most snags had been infected as live trees by dwarf mistletoe and the mistletoe probably contributed to their death. While dwarf mistletoe has traditionally been viewed as a forest pest because of reductions in timber volume, we suggest that in areas where management goals are not strictly focused on timber production, control of dwarf mistletoe may not be justified, practical, or even desirable. Our data suggest that dwarf mistletoes may have positive influence on wildlife habitat. Consequently, we suggest that eradication efforts be reconsidered given that dwarf mistletoes have been a part of these forest ecosystems for thousands, and possibly millions, of years.
Article
Control of mistletoe, a cause of tree decline and death, was investigated in north-eastern Victoria because of reports that mistletoe infestations had increased in recent years. The potential of four herbicides to control mistletoe (Amyema spp.) by injection of the trunks of host eucalypts was evaluated. Eleven eucalypt species were injected in different months in 1984 and 1985 with solutions of the translocatable herbicides GARLON, LONTREL, ROUNDUP and VELPAR. Evaluation of mistletoe control in conjunction with host health at 12 and 24 months after injection showed that mistletoes could be partially controlled on most species with certain herbicides. The best results were given by ROUNDUP (diluted 1:3 in water) or GARLON (1:4) injected at the rate of 1 mL per cut, with cuts spaced at 10 cm intervals around the lower trunk of the host tree. LONTREL and VELPAR gave unsatisfactory results, though they received only limited testing. The particular herbicide and month of injection that gave the greatest percentage control of mistletoes with no or limited host mortality varied according to the eucalypt species, although the most effective months were commonly January and June. Smaller host trees (< 30 cm diameter) were significantly more susceptible to death following injection than larger trees. This study has established that host injection with certain herbicides is a feasible and effective technique for reducing Amyema spp. populations on many eucalypt species. The results should be applicable to the 11 studied host eucalypt species infested with Amyema spp. growing elsewhere under similar conditions, but extrapolation to other species or genera (of host or mistletoe) would be inadvisable without further tests.
Article
Reproductive data from 83 female and 34 male ringtail possums, living in natural populations, have been accumulated over a 3-yr period (March 1960-May 1963). Reproductive tracts from 75 females killed during this period have been examined. Pseudocheirus is polyoestrous and breeds between the latter half of April and the end of November. The whole female reproductive tract and, in the male, the testes then undergo involution until the next breeding season. The majority of conceptions occur early in the breeding season when one to three eggs are shed and fertilized at one time. Supra-ovulation was not observed and the reproductive wastage was very low during pouch life. The mean litter size was two. It is exceptional for females to conceive a second time in one breeding season. Of the four teats, the posterior pair were selected by 85 % of the new-born young. The frequency of lactation in each posterior teat was approximately equal in 58 females. In advanced pregnancy (foetal head length, 6.5 mm) the subepithelial blood net of the uterine mucosa was more highly developed adjacent to a dorsal and ventral area of the vascular portion of the foetal yolksac. In these regions dense foetal blood vessel nets were formed by intense localized branching of the foetal vitelline veins on the yolksac. The foetal membrane, the allantois, was surprisingly large (8 mm diam.), and although not attached to the chorion possessed a conspicuous blood net in its base. An account of the histology of the ovary and reproductive tract includes the following reproductive conditions : juvenile, oestrus, early and late pregnancy, lactation, and anoestrus. Reproduction in Pseudocheirus is briefly compared to that of other marsupial species.
Article
The diet of the greater glider consisted almost entirely of eucalypt foliage, a poor source of nutriment. Eucalypt foliage varied widely according to tree species and leaf age in its concentration of both N and ligno-cellulose. The young leaves of eucalypts generally contained higher concentrations of N and lower concentrations of ligno-cellulose than mature leaves. Greater gliders ate young leaves whenever they were available, and throughout the year the animals foraged in trees with the greatest amounts of new leaf growth. A marked pattern of selection by greater gliders for particular eucalypt species, notably Eucalyptus viminalis, was related to the concentration of nutrients in the foliage. -from Authors
Article
Seven methods for predicting species diversity from inventory data were tested based on two model data sets. These data sets, derived from state automobile license plates observed in Mexico City and Lawrence, Kansas, had the advantage of providing known ‘communities’ to be sampled, allowing evaluation of different inference methods. Of the seven methods, those of Chao (1984), Clench (Soberón & LLorente, 1993), and model Mth of CAPTURE (Otis et al., 1978) were the most robust. Error inherent in calculations based on raw data was reduced substantially using a series of bootstrap manipulations. We recommend that optimal design of inventories should include stopping rules based on precision of results rather than on effort expended, an approach that offers considerable advantages, in terms of both accuracy of results and efficiency of sampling efforts.
Article
Mistletoes are a diverse group of parasitic plants with a worldwide distribution. The hemiparasitic growth form is critical to understanding their biology, buffering variation in resource availability that constrains the distribution and growth of most plants. This is manifested in many aspects of mistletoe life history, including extended phenologies, abundant and high-quality fruits and nectar, and few chemical or structural defenses. Most mistletoe species rely on animals for both pollination and fruit dispersal, and this leads to a broad range of mistletoe-animal interactions. In this review, I summarize research on mistletoe biology and synthesize results from studies of mistletoe-animal interactions. I consolidate records of mistletoe-vertebrate interactions, incorporating species from 97 vertebrate families recorded as consuming mistletoe and from 50 using mistletoe as nesting sites. There is widespread support for regarding mistletoe as a keystone resource, and all quantitative data are consistent with mistletoe functioning as a determinant of alpha diversity. Manipulative experiments are highlighted as a key priority, and six explicit predictions are provided to guide future experimental research. The facts which kept me longest scientifically orthodox are those of adapta-tion—the pollen-masses in Asclepias—the misseltoe, with its pollen carried by insects and seed by Birds—the woodpecker, with its feet and tail, beak and tongue, to climb the tree and secure insects. To talk of climate or Lamarckian habit producing such adaptation to other organic beings is futile. This diffi-culty, I believe I have surmounted. From a letter to Asa Gray by Charles Darwin, 1857.
Article
Spatial heterogeneity and patchy distributions of species in intact landscapes are likely to lead to complex and unpredictable distribution patterns in remnants following fragmentation. We examined this proposition in relation to the mistletoe Amyema miquelii, which exhibits a clumped distribution in Eucalyptus salmonophloia woodlands in the Western Australian wheatbelt. We sampled mistletoe distribution and abundance in 14 woodland fragments ranging from 2.4 to 60.5 ha and in 14 sections of roadside corridors. These sites represent all known fragments and corridors containing E. salmonophloia in a 1680-km2 study area. We found that large fragments were more likely to have mistletoes than small fragments, but that small fragments either contained many or few to no mistletoes, reflecting the way fragmentation “samples” the pre-existing distribution. Superimposed on this sampling effect is the influence of disturbance. Fragments subjected to stock grazing contained no mistletoes. This indicates that grazing modified the habitat either for the mistletoe itself, through changed water relations, or for the frugivorous birds which may disperse mistletoe fruit, through removal of the shrubby understory. Only one A. miquelii plant was found on 26.3 km of roadside corridor, despite tree densities in corridors being similar to those in fragments. Roadside areas are generally considered good habitat for mistletoes, and their absence suggested that fruit-dispersing birds either did not use the corridors or did not stay in them long enough to deposit mistletoe seeds. These results indicate that, in order to predict biotic responses to fragmentation, information on distribution patterns and scales of patchiness in the prefragmentation landscape is required and the effects of fragmentation per se are likely to be confounded by other factors such as disturbance. Furthermore, quantifying fragmentation effects is difficult because of the small sample sizes typical of highly fragmented landscapes. La heterogeneidad espacial y la distribución en parches de especies en paisajes intactos son proclives a conducir a patrones de distribución complejos e impredecibles en los remanentes que suceden a la fragmentatión. Examinamos este tema en relación al muérdago Amyema miquelii, una especie que exhibe una distribución contagiosa en los bosques de Eucalyptus salmonophloia del cinturón de trigo de Australia occidental. Muestreamos la distribucion y abundancia del muérdago, en 14 fragmentos de bosques que oscilaban entre 2.4 y 60.5 ha y en 14 secciones de corredores de los bordes de rutas. Estes sitios representan todos los fragmentos y corredores conocidos que contienen E. salmonophloia en los 1680 km2 del área de estudio. Encontramos que los fragmentos más grandes eran más proclives a tener muérdago que los fragmentos más chicos, pero los fragmentos más pequeños contenían mucho, poco o ningún muérdago, reflejando el modo en que la fragmentatión “muestrea” la distribución pre-existente. Superpuesto a este efecto de muestreo está la influencia de las perturbaciones. Los fragmentos sujetos a pastoreo de ganado no tuvieron muérdagos. Esta situación indica que el pastoreo modificó el hábitat para los muérdagos, a través del cambio en las relaciones hídricas, o bien para los pájaros frugívoros que pueden dispersar los frutos del muérdago, a través de la remoción de las área arbustivas del sotobosque. Sólamente una planta de A. miquelii fue encontrada en los 26.3 km de corredor a lo largo de la ruta, a pesar que la densidad de árboles en los corredores fue similar a la encontrada en los fragmentos. Las áreas a lo largo de las rutas son generalmente consideradas como buenos hábitats para los muérdagos, pero su ausencia sugiere que los pájaros dispersores de los frutos no utilizaron los corredores o bien no estuvieron un tiempo suficiente como para dspositar las semillas de muérdago. Estos resultados indican que, a efecto de predecir las respuestas bióticas de la fragmentación, se requiere información sobre los patrones de distributión y las escalas de la distributión contagiosa del paisaje previo a la fragmentación. Los resultados también indican que los efectos de la fragmentación en sí mismos tienden a confundirse con otros factores tales como la perturbación. Más aún, la cuantificación de los efectos de la fragmentación resulta dificil debidio al pequeño tamaño de muestra típico en los paisajes altamente fragmentados.
Article
Loranthaceous mistletoes are interesting because of their complex dependence on suitable host trees and avian dispersers and because of their patchy distribution at the landscape level. Although their over- and under-abundance in Australia and New Zealand have been widely documented, little attention has been given to the need for an ecosystem approach to their management. Although the current status of mistletoes is very different in Australia and New Zealand, some of the causal factors and the long-term effects of changes in mistletoe abundance are similar in the two countries. We suggest that mistletoe abundance in pre-European landscapes was dependent on a series of evolutionary and environmental filters relating to host specificity, pollination, dispersal, infection, environmental habitat quality, predation, and disturbance. European settlement modified these filters in a number of ways, resulting in either increases or decreases in mistletoe abundance. The three broad groups of changes that have occurred with European settlement involve fragmentation, predation, and altered disturbance regimes. Although managers have usually addressed mistletoe over- or under-abundance with short-term solutions (e.g., pruning infected trees), we suggest that management must address the underlying causes of the problems involving mistletoes. This requires an ecosystem approach to management that addresses both the direct and indirect causes of the current status of mistletoes.
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