Article

Factors Limiting the Survival of Corynephorus canescens (L.) Beauv. in Great Britain at the Northern Edge of Its Distribution

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Abstract

Corynephorus canescens presents two distributional problems in Great Britain; first, as a species with restricted distribution, and second, as one at the northern edge of its distribution. The first problem may be related to the past history of any one dune system and in particular the continuance in time and space of open sandy habitats of intermediate stability; the possible factors limiting Corynephorus at the northern edge of its distribution are considered in the body of the paper. The maintenance of Corynephorus populations is dependent on successful production and dispersal of seed, germination and seedling establishment. Reproductive capacity and seed viability are high. No dormancy mechanisms have been detected. Seed after-ripening is little affected by low temperature (0°C) and the seed is fully ripe eight weeks after anthesis. Germination is slowed down at temperatures below 15°C. Germination in the field is controlled by the availability of moisture for imbibition and its rate by temperature. The later the emergence date of seedlings in the field, the lower the chances of seedling survival. Seedling mortality occurs at a number of stages. It is concluded that the climate beyond the most northerly locality of Corynephorus in Great Britain (57°45′ N) is severe enough to have a cumulative effect on flowering date and seed germination sufficient to postpone emergence date of the seedlings beyond the critical time for their survival. /// Вопрос о распространении Corynephorus canescens в Великобритании рассматривается в двух аспектах: во-первых, это вид с ограниченным ареалом, во-вторых, Великобритания представляет северную область ареала данного вида. Лервая проблема связана с изучением возникновения и развития дюнного ландшафта, в частности с вопросом о длительности существования во времени и пространстве открытых песчаных местообитаний и их стабильности. В статье обсуждаются факторы, определяющие распределение Corynephorus в северной части его ареала. Состояние популяций Corynephorus эависит от продукции и распространения семян, а также от условий прорастания семян. Репродуктивная способность и жизнеспособность семян довольно высоки. Лериоды покоя у данного вида не установлены. Семена после созревания почти не чувствительны к действию низкой температуры, они полностью созревают через 8 недель после цветения. Всхожесть семян замедляется при температуре ниже 15°C. Всхожесть семян в полевых условиях зависит от количества доступной влаги, а скорость прорастания зависит от температуры. Чем позднее сроки появления проростков, тем менее благоприятны условия для их развития. Определена гибель проростков на разных фазах разнития. Установлено, что климатические условия севернее границы ареала Corynephorus в Великобритании /57°/45′ с.ш., около Лоссимута/ слишком суровы, и сроки цветения растении и появления проростков выходят за пределы критических периодов.

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... Tuttavia, viene riportata anche una riproduzione per via vegetativa in particolari condizioni (schulz, 1950;Frey & heNseN, 1995): C. canescens è infatti in grado di sopportare la copertura della sabbia, poiché i cespi presentano più livelli di crescita che possono produrre radici avventizie (Medwecka-korNas et al., 1966). Sebbene la produzione di semi risulti elevata, sia la vitalità che la dispersione del seme sono limitate, e la distanza di dispersione delle diaspore avviene nell'arco di pochi metri (Marshall, 1968;BöGer, 2007). La sua banca di semi, che non presentano una dormienza primaria, ha una breve durata (JeNtsch, 2001). ...
... Su queste ultime, in un'ottica di ottimizzazione delle risorse, dovrebbero essere di conseguenza concentrate primariamente le misure di conservazione sulla specie. Data la relativa scarsa capacità di dispersione dei semi (Marshall, 1968;BöGer, 2007), le popolazioni isolate, anche se di tipo puntiforme, potrebbero però essere un'importante sorgente di semi per la fondazione di nuove popolazioni, anche numericamente più consistenti di quelle originarie. Le popolazioni isolate dovrebbero subordinatamente ricevere anch'esse adeguate misure di conservazione. ...
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Research on populations of Corynephorus canescens (Poaceae) in the valley of River Ticino. Corynephorus canescens is a plant regarded as endangered species in Italy. The aim of this study was to fill the existing gaps about the knowledge of its distribution within a significant part of its Italian range, by collecting accurate data on the population size, in order to develop practical implications for the species conservation. The results demonstrated the essential role of the River Ticino in creating sandy deposits which are easily colonized by the species. The main risk factor for the species conservation could be the ongoing climate changes, especially events of severe summer drought because of which the populations are strongly injured.
... has occasionally been reported (Schulz 1950;Frey & Hensen 1995). Although seed production is high, seed viability and dispersal capacity of C. canescens are limited, as typical diaspore dispersal distances lie within only a few meters (Marshall 1968;B€ oger 2007). The habitat of C. canescens has been widespread during the last centuries, because forest logging and livestock grazing maintained dry acidic grasslands on coastal and inland dunes (Quinger & Meyer 1995;Jentsch & Beyschlag 2003). ...
... The placement of distribution borders is not trivial for C. canescens as the current range extends to the Atlantic coastlines. However, recent range maps place the distribution borders off the coast following assumed bioclimatic limitations (Marshall 1968;Hegi & Conert 1998;see Fig. 1). For the calculations of marginality we therefore took these sea areas into account. ...
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Corynephorus canescens (L.) P.Beauv. is an outbreeding, short-lived and wind-dispersed grass species, highly specialised on scattered and disturbance-dependent habitats of open sandy sites. Its distribution ranges from the Iberian Peninsula over Atlantic regions of Western and Central Europe, but excludes the two other classical European glacial refuge regions on the Apennine and Balkan Peninsulas. To investigate genetic patterns of this uncommon combination of ecological and biogeographic species characteristics, we analysed AFLP variation among 49 populations throughout the European distribution range, expecting (i) patterns of SW European glacial refugia and post-glacial expansion to the NE, (ii) decreasing genetic diversity from central to marginal populations, and (iii) interacting effects of high gene flow and disturbance-driven genetic drift. Decreasing genetic diversity from SW to NE and distinct gene pool clustering imply refugia on the Iberian Peninsula and in western France, from where range expansion originated towards the NE. High genetic diversity within and moderate genetic differentiation among populations, and a significant pattern of isolation-by-distance indicate a gene flow drift equilibrium within C. canescens, probably due to its restriction to scattered and dynamic habitats and limited dispersal distances. These features, as well as the re-colonisation history, were found to affect genetic diversity gradients from central to marginal populations. Our study emphasises the need for including the specific ecology into analyses of species (re–)colonisation histories and range centre–margin analyses. To account for discontinuous distributions, new indices of marginality were tested for their suitability in studies of centre–periphery gradients.This article is protected by copyright. All rights reserved.
... Many species exhibit a decline in seed production toward their range boundary (Pigott, 1968;Pigott & Huntley, 1981;Reinartz, 1984b;Eckert & Barrett, 1993;García et al ., 2000;Dorken & Eckert, 2001). The reproductive phase of the plant lifecycle shows particular sensitivity to climate (Marshall, 1968;Pigott, 1968;Pigott & Huntley, 1981;Houle & Filion, 1993;Despland & Houle, 1997;Woodward, 1997;García et al ., 2000). Variation in vegetative characters such as plant size (Marshall, 1968;Clevering et al ., 2001) and differential allocation to above-and below-ground organs (Benowicz et al ., 2000) toward a species' range limit have also been reported. ...
... The reproductive phase of the plant lifecycle shows particular sensitivity to climate (Marshall, 1968;Pigott, 1968;Pigott & Huntley, 1981;Houle & Filion, 1993;Despland & Houle, 1997;Woodward, 1997;García et al ., 2000). Variation in vegetative characters such as plant size (Marshall, 1968;Clevering et al ., 2001) and differential allocation to above-and below-ground organs (Benowicz et al ., 2000) toward a species' range limit have also been reported. Differences in plant size may ultimately be reflected in the reproductive success of the plant (Reinartz, 1984a,b;Primack, 1987;Wesselingh et al ., 1997). ...
Article
Summary • Patterns in population density and abundance, community composition, seed production and morphological traits were assessed across the UK geographical range of Cirsium acaule , Cirsium heterophyllum and Cirsium arvense based on the expectation that environmental favourability declines from core to periphery of a species range. • These traits were measured in natural populations along a latitudinal transect in the UK and using botanical survey data. •A significant decline in population density and seed production occurs approach- ing the range edges of C. acaule and C. heterophyllum . There is no latitudinal trend in these traits in the widespread C. arvense and no latitudinal pattern to variation in morphological traits or community composition in any of these species. • Although seed production is reduced at the range edge of C. acaule and C. het- erophyllum, peripheral populations of these species may persist through clonal reproduction. Low seed production may interact with reduced availability of favour- able habitat to limit range expansion in these species.
... Marginal populations are valuable sources of information on evolutionary processes (CARSON St;TEMPLETON 1984), and studies of marginal populations are often motivated in terms of conservation biology (e.g. MARSHALL 1968, HUTCHINGS 1987, BURGMAN et al. 1993. ...
... PIGOTT & WALTERS 1954, SKRE 1979, HUNTLEY & BmKS 1983. The dynamics of local populations may also be determined by climatic variation (MARSHALL 1968, MACK & PYKE 1983, BULLARD et al. 1987, DUNNE'rr et al. 1998. The possibility that the local abundance of a species is determined by the same factor~ that shape the species overall distribution range is discussed in several papers (e.g. ...
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... Therefore, we can only assume that, at this stage, the main part of soil formation under these communities consists of an accumulation of organic matter. In fact, soil profiles are absent under pioneer succession, but conditions are conducive to the encroachment of organisms with a high level of ecological requirements [52,74,75]. These organisms are algal communities (Figure 3). ...
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... These factors usually influence the survival and propagation ability of plants. For instance, Corynephorus canescens is widely distributed in mid and south Europe, and its northern distribution limit in Europe coincides with the 15˚C isotherm in July, as its germination and flowering are affected by low temperature [60]. The winter distribution and abundance patterns of several avian species are directly linked to their physiological limits, with the northern range limit being associated with the −4˚C isotherm of the average minimum January temperature [61]. ...
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Fritillaria spp. constitute important traditional Chinese medicinal plants. Xinjiang is one of two diversity hotspots in China in which eight Fritillaria species occur, two of which are endemic to the region. Furthermore, the phylogenetic relationships of Xinjiang Fritillaria species (including F. yuminensis) within the genus are unclear. In the present study, we sequenced the chloroplast (cp) genomes of seven Fritillaria species in Xinjiang using the Illumina HiSeq platform, with the aim of assessing the global structural patterns of the seven cp genomes and identifying highly variable cp DNA sequences. These were compared to previously sequenced Fritillaria cp genomes. Phylogenetic analysis was then used to evaluate the relationships of the Xinjiang species and assess the evolution of an undivided stigma. The seven cp genomes ranged from 151,764 to 152,112 bp, presenting a traditional quadripartite structure. The gene order and gene content of the seven cp genomes were identical. A comparison of the 13 cp genomes indicated that the structure is highly conserved. Ten highly divergent regions were identified that could be valuable in phylogenetic and population genetic studies. The phylogenetic relationships of the 13 Fritillaria species inferred from the protein-coding genes, large single-copy, small single-copy, and inverted repeat regions were identical and highly resolved. The phylogenetic relationships of the species corresponded with their geographic distribution patterns, in that the north group (consisting of eight species from Xinjiang and Heilongjiang in North China) and the south group (including six species from South China) were basically divided at 40°N. Species with an undivided stigma were not monophyletic, suggesting that this trait might have evolved several times in the genus.
... The species composition in coastal dunes is strongly correlated with climatic stresses, eolian dynamics, and soil development (Arens & Geelen, 2006;Honrado et al., 2010;Miller, Gornish, & Buckley, 2009;Provoost, Ampe, Bonte, Cosyns, & Hoffmann, 2004;van der Hagen, Geelen, & de Vries, 2008). The relationships between microclimate and patterns in vegetation composition have been extensively studied on sites differing in topography, for example, on polar-and equator-facing slopes (Bartholomeus, Witte, & Runhaar, 2011;De Jong & Klinkhamer, 1988;Marshall, 1968;Stoutjesdijk, 1959;Stoutjesdijk, 1977;Stoutjesdijk & Barkman, 1992;Ten Harkel, 1992). ...
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... Even fewer studies report a quantitative estimate of lifetime fitness or population growth rate based on multiple fitness components across the life cycle (but see Purves 2009). This is of particular significance when the accumulation of small fitness differences across the life cycle yields substantial differences in overall fitness (Marshall 1968). When studies are grouped by species (rather than separated by fitness components), 49 out of 73 found at least one of the examined fitness components to be lower at the range edge compared to the range center. ...
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... We examined seed germination and seedling establishment, which are critical to population invasion and persistence and are important factors in species' responses to global change (Williams et al. 2007). Furthermore, seed germination and seedling growth are generally susceptible to extreme temperature changes (Marshall 1968;Woodward et al. 1990). Ecological and physiological traits such as seed germination, RGR, and other characteristics were examined to explore the response of these species to extreme temperatures. ...
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Climate change and plant invasion are two of the most important ecological issues facing the world today. Extreme events are likely to play an important role in plant invasion. For example, tolerance to temperature stress is critical for plant germination and survival of seedlings. Nonnative invasive species tend to differ from co-occurring native species in several traits. Increased mean temperatures are known to enhance the risk of plant invasions, but few experimental studies have linked plant invasion to both increasing mean temperature and extreme (low and high) temperatures. Ten plant species from Asteraceae (six nonnative invasive and four native species) were chosen and six temperatures (extremely low, average winter, average annual, average summer, high and extremely high) were used to test the effects of extreme temperatures on plant invasion in southern China. The results showed that nonnative invasive plant species (IS) germinated more readily and the seedlings grew better than those of native plant species (NS) at high temperatures, suggesting that global warming may facilitate invasion. Extreme temperatures decreased the seed germination rate and seedling growth of both IS and NS, although NS were more tolerant of extremely low temperatures (5/0 °C). IS, in turn, were more tolerant of extremely high temperatures (40/35 °C). Extreme high temperatures may increase the risk of plant invasion because IS seedlings are better able to become established, whereas low temperatures may hinder invasion. In addition, the species-specific differences in plant origin (IS and NS) and temperature tolerance were correlated with other climatic factors and should be considered in managing invasive species in a changing world.
... We examined seeds and seedlings because these life history stages are under strong selective pressure, particularly as they relate to climatic factors. Unsuitable timing of germination can result in exposure of seedlings to fatal freeze events (Marshall 1968;Woodward et al. 1990), and plants are most vulnerable to cold temperatures and other environmental stresses at the seedling stage (Larcher 2003). Additionally, the presence of profuse seed production among isolated Chinese tallow transplanted as saplings to sites well beyond its current invasive range (I. ...
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... The factors that constrain species' ranges have long been a focus of ecological research (e.g., Darwin 1859;MacArthur 1972), and are currently important because of concern over the spread of non-native species (Vitousek et al. 1996) and strong interest in predicting distributional changes in response to climate change Morin et al. 2008). If climate continues to follow the prevailing warming trend (IPCC 2007), rising temperatures could expand the ranges of non-native species with limited cold and frost tolerance (Jarnevich and Stohlgren 2009;Kriticos et al. 2003). ...
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... Even fewer studies report a quantitative estimate of lifetime fitness or population growth rate based on multiple fitness components across the life cycle (but see Purves 2009). This is of particular significance when the accumulation of small fitness differences across the life cycle yields substantial differences in overall fitness (Marshall 1968). When studies are grouped by species (rather than separated by fitness components), 49 out of 73 found at least one of the examined fitness components to be lower at the range edge compared to the range center. ...
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Species range limits involve many aspects of evolution and ecology, from species distribution and abundance to the evolution of niches. Theory suggests myriad processes by which range limits arise, including competitive exclusion, Allee effects, and gene swamping; however, most models remain empirically untested. Range limits are correlated with a number of abiotic and biotic factors, but further experimentation is needed to understand underlying mechanisms. Range edges are characterized by increased genetic isolation, genetic differentiation, and variability in individual and population performance, but evidence for decreased abundance and fitness is lacking. Evolution of range limits is understudied in natural systems; in particular, the role of gene flow in shaping range limits is unknown. Biological invasions and rapid distribution shifts caused by climate change represent large-scale experiments on the underlying dynamics of range limits. A better fusion of experimentation and theory will advance our...
... In the northern hemisphere, low temperatures often limit the viability of plant populations at their northern boundary (e.g. Marshall 1978;Woodward 1990Woodward , 1997Pigott 1992;Loik & Nobel 1993), while water availability is the main limiting factor at the southern boundary (e.g. Pigott & Pigott 1993;Gardner & Fisher 1996;GarcõÂ a et al. 1999). ...
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1. The geographical variation of seed production, predation and abortion was analysed in Juniperus communis for 31 populations in seven distinct regions throughout the species' distribution range in Europe, including both the northern and southern boundaries. 2. The number of seeds per cone and the number of filled seeds per cone varied significantly between geographical regions and among populations within regions. Populations from the Mediterranean mountains (south-east Spain) showed the highest values in the number of seeds per cone but the lowest values in the number of filled seeds per cone. 3. Losses due to predispersal seed predation varied significantly among populations within a region but not between regions, suggesting that predation incidence depends on local-scale factors. Seed abortion rates were higher in southern Iberian populations than in the other regions, and varied significantly among populations and regions. As a result of predation and abortion, seed production was lowest in the Iberian regions. 4. Seed abortion showed a significant quadratic relationship with latitude, with higher values of abortion at either end of the gradient, but particularly at the southern limit. 5. The production of filled seeds declined gradually towards both northern and southern distribution limits. In the Mediterranean mountains (southern limit), low seed production coincided with a marked limitation placed upon natural regeneration by summer drought, leading to a demographic bottleneck in populations. Although seed abortion levels were relatively high in the subarctic tundra (northern limit) populations, they were free from predispersal seed predators, suggesting that population viability here may be under less pressure.
... The geographical range of many plant species is determined by climate (Woodward & Williams 1987; Woodward 1990; Pigott 1992; Archibold 1995). In the northern hemisphere, low temperatures often limit the viability of plant populations at their northern boundary (e.g. Marshall 1978; Woodward 1990 Woodward , 1997 Pigott 1992; Loik & Nobel 1993), while water availability is the main limiting factor at the southern boundary (e.g. Pigott & Pigott 1993; Gardner & Fisher 1996; GarcõÂ a et al. 1999). ...
Article
1 The geographical variation of seed production, predation and abortion was analysed in Juniperus communis for 31 populations in seven distinct regions throughout the species’ distribution range in Europe, including both the northern and southern boundaries. 2 The number of seeds per cone and the number of filled seeds per cone varied significantly between geographical regions and among populations within regions. Populations from the Mediterranean mountains (south-east Spain) showed the highest values in the number of seeds per cone but the lowest values in the number of filled seeds per cone. 3 Losses due to predispersal seed predation varied significantly among populations within a region but not between regions, suggesting that predation incidence depends on local-scale factors. Seed abortion rates were higher in southern Iberian populations than in the other regions, and varied significantly among populations and regions. As a result of predation and abortion, seed production was lowest in the Iberian regions. 4 Seed abortion showed a significant quadratic relationship with latitude, with higher values of abortion at either end of the gradient, but particularly at the southern limit. 5 The production of filled seeds declined gradually towards both northern and southern distribution limits. In the Mediterranean mountains (southern limit), low seed production coincided with a marked limitation placed upon natural regeneration by summer drought, leading to a demographic bottleneck in populations. Although seed abortion levels were relatively high in the subarctic tundra (northern limit) populations, they were free from predispersal seed predators, suggesting that population viability here may be under less pressure.
... Corynephorus canescens and the sheep's sorrel (Rumex acetosella L.) co-occur in all three stages. Corynephorus canescens is an upright, wintergreen biennial grass which typically dies after reproduction (Marshall 1968). There is however, evidence that C. canescens is not strictly biennial and that clonal growth is to some extent co-occurring with the dieback of the old tussocks (Frey and Hensen 1995; Marshall 1967). ...
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In this study we investigated the temporal variability of N-source utilization of pioneer plant species in different early successional stages of dry acidic grasslands. Current theory states that plant species occupy distinct ecological niches and that there are species-specific, temporal N-uptake patterns. We hypothesized that small-scale dynamics in the natural habitat may affect niche differentiation among plant species. We investigated N-uptake patterns of two co-occurring plant species from different functional groups (Corynephorus canescens, Rumex acetosella) under natural conditions using 15N-labeled nitrate and ammonium in three different early successional stages during early and late summer. We found (1) marked seasonal dynamics with respect to N-uptake and N-source partitioning, and (2) different uptake rates across successional stages but a similar N-form utilization of both species. Nitrate was the main N-source in the early and later successional stages, but a shift towards enhanced ammonium uptake occurred at the cryptogam stage in June. Both species increased N-uptake in the later successional stage in June, which was associated with increasing plant biomass in C. canescens, whereas R. acetosella showed no significant differences in plant biomass and root/shoot-ratio between successional stages. Ammonium uptake decreased in both species across all stages with increasing drought. Nevertheless, the peak time of N-uptake differed between the successional stages: in the early successional site, with the lowest soil N, plants were able to extend N-uptake into the drier season when uptake rates in the other successional stages had already declined markedly. Hence, we found a pronounced adjustment in the realized niches of co-occurring plant species with respect to N-uptake. Our results indicate that ecological niches can be highly dynamic and that niche sharing between plant species may occur instead of niche partitioning.
... Many other investigations of distribution limits focus on individuals, asking whether survival and reproduction decrease toward the range margin (Marshall 1968;Pigott and Huntley 1981;McKee and Richards 1996;Garcia et al. 2000;Hennenberg and Bruelheide 2003;Angert and Schemske 2005), and, if so, which environmental variables are responsible for variation in components of fitness (McNab 1973;Root 1988;Cumming 2002;Angert 2006b). However, even when ecological and demographic factors that limit the range are identified, it remains unclear why natural selection does not continually improve adaptation to limiting environmental variables and overcome current distribution limits. ...
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Every species occupies a restricted geographic distribution, but it is unclear why natural selection at the range margin fails to increase tolerance to limiting environmental variables and thereby allow continual range expansion. Models indicate that the interplay of demographic asymmetries, dispersal, divergent natural selection, and adaptive trade-offs across spatially varying environments can give rise to stable range limits. Here we examine sister species of the monkeyflowers Mimulus cardinalis and M. lewisii to identify traits that might contribute to the evolution of the species' ranges and to ask whether adaptive trade-offs between environments can limit their geographic distribution. In the Sierra Nevada Mountains of California, M. cardinalis is found from low to mid elevation and M. lewisii is found from mid to high elevation. We transplanted segregating populations of interspecific hybrids to low and high elevation and cross-pollinated those that survived to flowering to create selected populations that evolved at low or high elevation. When grown in a common environment, the progeny of hybrids selected at high elevation flowered earlier compared to a greenhouse control population, whereas hybrids selected at low elevation displayed increased warm-temperature photosynthetic capacity. If adaptation to one environment entails a cost to adaptation in other environments, then selected hybrid populations should display reduced fitness, relative to an unselected control population, when grown in an environment in which they were not selected. Two such trade-offs were observed in this study, where hybrids selected at high elevation displayed reduced biomass when grown in temperatures characteristic of low elevation and hybrids selected at low elevation showed reduced resistance to freezing. These results identify traits under selection for range expansion and suggest that adaptive trade-offs can contribute to limiting the geographic distribution of species.
... A more critical test for reduced fitness in marginal populations involves direct observation of fitness components across species ranges. Such studies have often found lower survival of certain life-history stages or reduced fecundity at the range margin relative to the range center (Marshall 1968;Pigott and Huntley 1981;McKee and Richards 1996;Garcia et al. 2000;Hennenberg and Bruelheide 2003). Unfortunately, the demographic consequences for such reductions in fitness are generally unclear. ...
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Every species occupies a limited geographic area, but it remains unclear why traits that limit distribution do not evolve to allow range expansion. Hypotheses for the evolutionary stability of geographic ranges assume that species are maladapted at the range boundary and unfit beyond the current range, but this assumption has rarely been tested. To examine how fitness varies across species' ranges, we reciprocally transplanted two species of monkeyflowers, Mimulus cardinalis and M. lewisii, within and beyond their present elevation ranges. We used individuals of known parentage from populations collected across the elevation ranges of both species to examine whether populations are adapted to position within the range. For both species we found the greatest average fitness at elevations central within the range, reduced fitness at the range margin, and zero or near-zero fitness when transplanted beyond their present elevation range limits. However, the underlying causes of fitness variation differed between the species. At high elevations beyond its range, M. cardinalis displayed reduced growth and fecundity, whereas at low elevations M. lewisii experienced high mortality. Weak differences in performance were observed among populations within each species and these were not related to elevation of origin. Low fitness of both species at their range margin and weak differentiation among populations within each species suggest that adaptation to the environment at and beyond the range margin is hindered, illustrating that range margins provide an interesting system in which to study limits to adaptation.
... Consistent with this characterization, species abundance (i.e., local population density) often decreases with distance from the range center, presumably in response to an increasingly unfavorable environment (McClure andPrice 1976, Brown et al. 1996, but see Sagarin and Gaines 2002). Observations of individual performance across the range frequently find lower survival or reduced fecundity at the range margin relative to the range center (Marshall 1968, Pigott and Huntley 1981, Jump and Woodward 2003. However, whether reductions in some fitness components impact population growth and persistence is not always evident. ...
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Every species occupies a limited geographic area, but how spatiotemporal environmental variation affects individual and population fitness to create range limits is not well understood. Because range boundaries arise where, on average, populations are more likely to go extinct than to persist, range limits are an inherently population-level problem for which a demographic framework is useful. In this study, I compare demographic parameters and population dynamics between central and marginal populations of monkeyflowers, Mimulus cardinalis and M. lewisii, along an elevation gradient spanning both species' ranges. Central and marginal populations of both species differed in survival and fecundity. For M. lewisii, these components of fitness were higher in central than in marginal populations, but for M. cardinalis the converse was true. To assess spatiotemporal variation in population dynamics, I used transition matrix models to estimate asymptotic population growth rates (lambda) and found that population growth rates of M. lewisii were highest at the range center and reduced at the range margin. Population growth rates of M. cardinalis were highest at the range margin and greatly reduced at the range center. Life table response analysis decomposed spatiotemporal variation in lambda into contributions from each transition between life stages, finding that transitions from large nonreproductive and reproductive plants to the seed class and stasis in the reproductive class made the largest contributions to spatial differences in lambda. These transitions had only low to moderate sensitivities, indicating that differences in projected population growth rates resulted mainly from observed differences in transition matrix parameters and their underlying vital rates.
... Both ecological and genetic factors may serve to limit the geographical and/or ecological distribution of a species (Marshall 1968; Silander and Antonovics 1979; Levin and Clay 1984; Hoffmann and Blows 1994). ...
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Although invasive plant species often have a hybrid ancestry, unambiguous evidence that hybridization has stimulated the evolution of invasive behaviors has been difficult to come by. Here, we briefly review how hybridization might contribute to the colonization of novel habitats, range expansions, and invasiveness and then describe work on hybrid sunflowers that forges a direct link between hybridization and ecological divergence. We first discuss the invasion of Texas by the common sunflower and show that the introgression of chromosomal segments from a locally adapted species may have facilitated range expansion. We then present evidence that the colonization of sand dune, desert floor, and salt marsh habitats by three hybrid sunflower species was made possible by selection on extreme or "transgressive" phenotypes generated by hybridization. This body of work corroborates earlier claims regarding the role of hybridization in adaptive evolution and provides an experimental and conceptual framework for ongoing studies in this area.
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Ein vollständiger Bericht über alle Floren-Neuerscheinungen kann nicht die Aufgabe der „Fortschritte“ sein. Er wird für Europa und Nordafrika alljährlich im „Index to european taxonomic literature“ gegeben (BRUMMITT u. FERGUSON). Dazu kommt seit 1970 regelmäßig eine von EHRENDORFER u. JÄGER zusammengestellte Liste der neuen außereuropäischen Floren in “Taxon”. Die zahlreichen mitteleuropäischen Floren und andere Werke über mitteleuropäische Gefäßpflanzen erfaßt eine Bibliographie von HAMANN u. WAGENITZ. Das von STEENIS herausgebene „Flora Malesiana Bulletin“ (1969: Band 23 und 24) nennt und rezensiert nicht nur Floren-Neuerscheinungen aus dem Gebiet der Flora Malesiana, sondern auch aus anderen tropischen, subtropischen und südhemisphärisch-außertropischen Gebieten. Die tropischen Floren werden auch in dem von der O.R.S.T.O.M. herausgegebenen bibliographischen Index der tropischen Botanik (MOUTON u. GUILLAUMET) erfaßt. Über den Fortgang der Arbeit an den afrikanischen Florenwerken wird in den Beiträgen zum A.E.T.F.A.T. Symposium 1966 (Acta Phytogeogr. Suec. 54, 1968: 285–307) und seit 1953 im A.E.T.F.A.T.-Bulletin berichtet. Auch in der Sowjetunion geben neue Übersichtsreferate Aufschluß über den Stand der floristischen Erforschung des Landes (KIRPITSCHNIKOW über die baltischen Republiken, SERGIEWSKAJA (1) über Westsibirien).
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The preceding chapters have followed an interconnected path through the fields of green roof research to converge in this chapter on some emerging principles for the design of green roof ecosystems that extend beyond the garden aesthetic. Understanding green roof ecosystems in time and space becomes critical to good ecological design and the desire to protect and improve biodiversity in all its forms. Scale plays a central role in ecology, providing context to understanding patterns across the space-time continuum within the local, regional, and global landscape. Review of green roof projects and research literature indicates that beyond local concern to create authentic habitat, green roof design and research has paid scarce attention to scalar relationships. As we explain in this chapter, paying attention to scale has implications for the ecological relevance of a green roof project at both socio-political and biological levels. Contextualizing how a roof will fit into time and space establishes its place on the planet and its ecological role in the landscape. Scale also plays a role in the recruitment, establishment, and regeneration of species on a roof, that in turn sets the management path towards design success and long-term survival of the roof ecosystems created.
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1 Demographic processes were followed over seven successive years in an outlying population of Fumana procumbens on its northern range-limit on the Baltic island of Oland. Comparisons were made between three sites which represented different types of habitat, vegetation and grazing regime. Demographic variation and reproductive success were related to variation in local weather conditions and microclimate. 2 Fumana procumbens was patchily distributed within the study sites, with the spatial scale of the patchiness varying between the three sites. Patch structure and density distribution within sites were related to grazing intensity, vegetation type and the availability of fissures in the underlying bedrock. 3 Seed production and seed quality varied in space and time. The best overall reproductive success was found at the occasionally grazed site with thin soil, low cover of vascular plants, high cover of bryophytes and a low degree of shading. Low temperatures and drought in early summer delayed the onset of flowering and caused a decrease in seed set in all sites. 4 Stage-based transition population matrix analyses showed that life-stage distribution and projected population growth rates (lambda) varied between years, reflecting demographic succession in the population and temporal variation in local climate. 5 Elasticity analyses of the matrices showed that the life-history transition probabilities that had the greatest influence on the predicted population growth rates (lambda) were those concerned with survival, particularly in the reproductive stages. Extended periods with low precipitation or low temperatures, which increase adult mortality and lower seed production, may thus have dramatic effects on population sizes. 6 Reproduction, establishment and survival in Fumana procumbens was found to depend to a large extent on local climatic variation. The long-term existence of the Baltic range-margin populations of F. procumbens is likely to depend ultimately on future climatic trends. On a shorter time-scale, the survival of the species on Oland is likely to depend on the continued maintenance of open habitats by grazing.
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In order to predict future range shifts for invasive species it is important to explore their ability to acclimate to the new environment and understand physiological and reproductive constraints controlling their distribution. My dissertation studied mechanisms by which temperature may affect the distribution of two of the most aggressive plant invaders in North America, Bromus tectorum and Bromus rubens. While Bromus tectorum is dominant in the “cold desert” steppes of the Intermountain region of western North America, B. rubens is one of the severe grass invaders in the “hot deserts” of southwestern North America. I first evaluated whether winter freezing tolerance is the mechanism responsible for the distinct northern range limits of Bromus species. Bromus rubens has a slower rate of freezing acclimation that leads to intolerance of sudden, late-autumn reductions in temperature below -12°C, Bromus tectorum, by contrast, cold hardens rapidly and is not impacted by the sudden severe late-autumn cold. Photosynthetic response to temperature does not explain their current range separation. Bromus species differ little in their photosynthetic temperature responses and the acclimation pattern of photosynthesis. Both species acclimated to a broad iii range of temperature through the amelioration of Pi regeneration limitation at sub-optimal temperatures and improved carboxylation capacity above the thermal optimum which probably resulted from increased thermostability of Rubisco activase. The effect of elevated temperatures during flowering on the seed yield of Bromus species demonstrates that neither species produces seed at 36°C and above. These thresholds are close to temperatures encountered during flowering in their natural environment. In summary, climatic changes will cause northward range expansion of Bromus species due to less severe autumn and winter, while reproductive failure could cause range contraction at their southern margins.
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Rare vascular plant species are endangered worldwide. Population losses are most commonly caused by human-related factors. Conservation management seeks to halt this adverse trend and if possible, to enhance long-lasting self-sustainable populations. In general, rare species are poorly recruited from seed banks, or disperse themselves very poorly. It may be a management option to translocate such plants by seeds and/or transplants. This paper asks which problems may be faced. It is argued that translocation is only acceptable if it is based on knowledge of species biology and ecology and the size and structure of its geographic range through time. Such knowledge of rare species is often lacking. The finite management goal can only be achieved if conservationists closely cooperate with both ecologists and geneticists.
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With increasing elevation and corresponding changes in the macroclimate, forest zones in the Intermountain Region of western North America are often dominated in turn by Pinus ponderosa, Pseudotsuga menziesii, Abies grandis, an Thuja plicata. Bromus tectorum (cheatgrass), and introduced annual grass now abundant in the Region's steppe, is uncommon in mature stands representative of these forest zones. In order to determine whether B. tectorum is largely excluded from these forests by insufficient seed dispersal or environmental restriction(s), the grass's demography was compared in each of four years among populations experimentally-introduced into mature forests. The number of recruits did not differ among the Pinus, Pseudotsuga, and Abies sites; recruitment was however significantly lower on the coolest site dominated by Thuja. Emergence in both the low elevation Pinus and Pseudotsuga sites was about the same in autumn, winter, and spring. In the cooler, moister Abies and Thuja sites, emergence was limited to autumn and early winter. Survival in these forest sites ranged between 0 and 87%. The percentage of the total population to survive until harvest was highest in the Pseudotsuga site, intermediate in the Pinus and Abies sites, and lowest in the Thuja site. Compared with B. tectorum in the steppe, the surviving plants were small, and few produced seeds. All parents were members of either the autumn or winter cohort, and most parents produced only one seed. No seeds were produced at the Thuja site. Although phenotypic plasticity apparently contributes to the wide ecological amplitude of this grass, its growing season on these sites in most years is too short for it to reproduce. Consequently, these forest zones broadly define the current environmental limits to the distribution of cheatgrass in this portion of its new geographic range.
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In the geologic past, natural climate changes have caused large-scale geographical shifts in species' ranges, changes in the species composition of biological communities, and species extinctions. If the widely predicted greenhouse effect occurs, natural ecosystems will respond in similar ways as in the past, but the effects will be more severe because of the extremely rapid rate of the projected change. Moreover, population reduction and habitat destruction due to human activities will prevent many species from colonizing new habitat when their old becomes unsuitable. The synergy between climate change and habitat destruction would threaten many more species than either factor alone.These effects would be pronounced in temperate and arctic forests, where temperature increases are projected to be relatively large. Localized species might face extinction, while widespread forest trees are likely to survive in some parts of their range. New northward habitat will become suitable even as die-offs of tree species occur to the south. However, it may be difficult for many species to take advantage of this new habitat because dispersal rates for tree species are very slow relative to the rate of warming, and therefore ranges of even many widespread species are likely to show a net decrease during the next century. Range retractions will be proximally caused by temperature and precipitation changes, increases in fires, changes in the ranges and severity of pests and pathogens, changes in competitive interactions, and additional effects of non-climatic stress such as acid rain and low-level ozone. Changes in species composition will have large effects on local and regional economies and biological diversity.
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