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1.
Barbara Jones  C. Gliddon 《Plant Ecology》1999,141(1-2):151-161
Concern regarding the conservation status of small, isolated populations of the arctic-alpine plant species Lloydia serotina prompted research to establish the status and performance of this species in Wales, in comparison with large populations in its more typical alpine habitat. Relationships between reproductive strategies and genetic variation were investigated in a number of populations, representing a wide habitat, geographic and population size range. In all populations, vegetative reproduction predominates over sexual reproduction, but seed produced is viable and germinates readily under controlled conditions. Smaller, peripheral populations produced fewer flowers and seeds than the larger ones, but all populations studied supported significant percentages (>30%) of male plants, due to either the occurrence of androdioecy in this species or to a resource limited breeding system. Analysis of allozyme variation in sixteen populations from North America, the European Alps and Wales showed lower levels of genetic variation in smaller populations which averaged 1.1–1.2 alleles per locus and 10–20% of loci polymorphic, whereas larger populations averaged 1.4 alleles per locus and 30–40% polymorphic loci. This applied especially to the most northerly and southerly populations in North America, suggesting the occurrence of genetic drift in these small, peripheral populations. F-statistics suggest relatively high levels of differentiation among smaller populations, even among those closely related geographically, but genetic variation has been retained in all but one population, possibly due to infrequent sexual reproduction by long lived clones. RAPD analysis of four small populations in Wales provided further evidence of clonal growth and possible inbreeding dominating a mixed mating reproductive system with consequent genetic structuring in these populations.  相似文献   

2.
Many endangered species worldwide are found in remnant populations, often within fragmented landscapes. However, when possible, an understanding of the natural extent of population structure and dispersal behaviour of threatened species would assist in their conservation and management. The brush-tailed rock-wallaby (Petrogale penicillata), a once abundant and widespread rock-wallaby species across southeastern Australia, has become nearly extinct across much of the southern part of its range. However, the northern part of the species’ range still sustains many small colonies closely distributed across suitable habitat, providing a rare opportunity to investigate the natural population dynamics of a listed threatened species. We used 12 microsatellite markers to investigate genetic diversity, population structure and gene flow among brush-tailed rock-wallaby colonies within and among two valley regions with continuous habitat in southeast Queensland. We documented high and significant levels of population genetic structure between rock-wallaby colonies embedded in continuous escarpment habitat and forest. We found a strong and significant pattern of isolation-by-distance among colonies indicating restricted gene flow over a small geographic scale ( <10 km) and conclude that gene flow is more likely limited by intrinsic factors rather than environmental factors. In addition, we provide evidence that genetic diversity was significantly lower in colonies located in a more isolated valley region compared to colonies located in a valley region surrounded by continuous habitat. These findings shed light on the processes that have resulted in the endangered status of rock-wallaby species in Australia and they have strong implications for the conservation and management of both the remaining ‘connected’8 brush-tailed rock-wallaby colonies in the northern parts of the species’8 range and the remnant endangered populations in the south.  相似文献   

3.
A proactive approach to conservation must be predictive, anticipating how habitats will change and which species are likely to decline or prosper. We use composite species distribution modelling to identify suitable habitats for 18 members of the North American Atlantic Coastal Plain Flora (ACPF) since the Last Glacial Maximum and project these into the future. We then use Scirpus longii (Cyperaceae), a globally imperiled ACPF sedge with many of the characteristics of extinction vulnerability, as a case study. We integrate phylogeographical and population genetic analyses and species distribution modelling to develop a broad view of its current condition and prognosis for conservation. We use genotyping‐by‐sequencing to characterize the genomes of 142 S. longii individuals from 20 populations distributed throughout its range (New Jersey to Nova Scotia). We measure the distribution of genetic diversity in the species and reconstruct its phylogeographical history using the snapp and rase models. Extant populations of S. longii originated from a single refugium south of the Laurentide ice sheet around 25 ka. The genetic diversity of S. longii is exceedingly low, populations exhibit little genetic structure and the species is slightly inbred. Projected climate scenarios indicate that nearly half of extant populations of S. longii will be exposed to unsuitable climate by 2070. Similar changes in suitable habitat will occur for many other northern ACPF species—centres of diversity will shift northward and Nova Scotia may become the last refuges for those species not extinguished.  相似文献   

4.
Estimates of density and population size are fundamental in assessing population trends and ultimately in informing conservation management. Although the abundance of raptors is often expressed as indices of relative abundance, these can be poor correlates of absolute density. In 2008–2009, I calculated the absolute density and population size of Gray‐backed Hawks (Pseudastur occidentalis), an endangered species and Tumbesian endemic, using line transect counts in four different habitat types in a protected area in northwestern Peru. The absolute density of Gray‐backed Hawks in northwest Peru was estimated to be 0.65 individuals km?2, and the most suitable habitat for the species was located in the provinces of Manabí, Guayas, and Santa Elena in Ecuador, and Tumbes and Piura departments in Peru. The population of Gray‐backed Hawks in my study areas in Tumbes was estimated to be 136, with 94% occurring in dry deciduous and deciduous forest. Because ~60% of all detections in my study were made outside strictly protected areas, including the recently created Angostura‐Faical Regional Conservation Area, conservation of the remaining, non‐protected forests patches in Peru and Ecuador should be a high priority. The current global population of Gray‐backed Hawks has been estimated to be between 250 and 999 birds and declining due to ongoing habitat destruction and fragmentation. Small populations in small habitat fragments, like those in my study area, have high conservation potential, provided that populations are not isolated, and hence should be the focus of constant monitoring.  相似文献   

5.
Ancient trees remaining in natural areas from once widespread forest due to overexploitation and habitat modification would naturally regenerate to form small isolated populations after the halting of disturbance. The genetic processes and consequence of this regeneration are generally unknown, which prevents the effective conservation and management of these populations. One such population, an Erythrophleum fordii population, is located in Dinghushan National Nature Reserve (China). Owing to the remarkably huge trunk of the sole ancient tree (KG) relative to the other individuals in the population, the local people and local tourism administration presume that this population has developed solely from KG. We found, using genetic diversity analyses, that contrary to this presumption, the population might have regenerated from several founders with diverse genetic backgrounds. Severe degradation of genetic diversity within the population did not take place, rather, it possessed the potential ability to maintain and recover gradually with population development. According to the results of simulations, we found that the longevity of tree species with iteroparity offers the potential to maintain genetic diversity in small isolated populations. The results from this study will benefit the restoration and conservation of the endangered species E. fordii, and of other congener species and tree species with similar life history traits.  相似文献   

6.
In the face of global climate change, organisms may respond to temperature increases by shifting their ranges poleward or to higher altitudes. However, the direction of range shifts in riverine systems is less clear. Because rivers are dendritic networks, there is only one dispersal route from any given location to another. Thus, range shifts are only possible if branches are connected by suitable habitat, and stream‐dwelling organisms can disperse through these branches. We used Cumberlandia monodonta (Bivalvia: Unionoida: Margaritiferidae) as a model species to investigate the effects of climate change on population connectivity because a majority of contemporary populations are panmictic. We combined ecological niche models (ENMs) with population genetic simulations to investigate the effects of climate change on population connectivity and genetic diversity of C. monodonta. The ENMs were constructed using bioclimatic and landscape data to project shifts in suitable habitat under future climate scenarios. We then used forward‐time simulations to project potential changes in genetic diversity and population connectivity based on these range shifts. ENM results under current conditions indicated long stretches of highly suitable habitat in rivers where C. monodonta persists; populations in the upper Mississippi River remain connected by suitable habitat that does not impede gene flow. Future climate scenarios projected northward and headwater‐ward range contraction and drastic declines in habitat suitability for most extant populations throughout the Mississippi River Basin. Simulations indicated that climate change would greatly reduce genetic diversity and connectivity across populations. Results suggest that a single, large population of C. monodonta will become further fragmented into smaller populations, each of which will be isolated and begin to differentiate genetically. Because C. monodonta is a widely distributed species and purely aquatic, our results suggest that persistence and connectivity of stream‐dwelling organisms will be significantly altered in response to future climate change.  相似文献   

7.
Intraspecific genetic diversity governs the potential of species to prevail in the face of environmental or ecological challenges; therefore, its protection is critical. The Indo-Australian Archipelago (IAA) is a significant reservoir of the world's marine biodiversity and a region of high conservation priority. Yet, despite indications that the IAA may harbour greater intraspecific variation, multiple-locus genetic diversity data are limited. We investigated microsatellite DNA variation in Pinctada maxima populations from the IAA to elucidate potential factors influencing levels of genetic diversity in the region. Results indicate that genetic diversity decreases as the geographical distance away from central Indonesia increases, and that populations located towards the centre of P. maxima 's range are more genetically diverse than those located peripherally ( P <  0.01). Significant partitioning of genetic variation was identified ( F ST = 0.027; R ST = 0.023, P  < 0.001) and indicates that historical biogeographical episodes or oceanographic factors have shaped present population genetic structure. We propose that the genetic diversity peak in P. maxima populations may be due to (i) an abundance of suitable habitat within the IAA, meaning larger, more temporally stable populations can be maintained and are less likely to encounter genetic bottlenecks; and/or (ii) the close proximity of biogeographical barriers around central Indonesia results in increased genetic diversity in the region because of admixture of genetically divergent populations. We encourage further genetic diversity studies of IAA marine biota to confirm whether this region has a significant role in maintaining intraspecific diversity, which will greatly assist the planning and efficacy of future conservation efforts.  相似文献   

8.
Changes in the frequency and severity of extreme weather may introduce new threats to species that are already under stress from gradual habitat loss and climate change. We provide a probabilistic framework that quantifies potential threats by applying concepts from ecological resilience to single populations. Our approach uses computation to compare disturbance–impacted projections to a population's normal range of variation, quantifying the full range of potential impacts. We illustrate this framework with projection models for coastal birds, which are commonly depicted as vulnerable to disturbances, especially hurricanes and oil spills. We found that populations of coastal specialists are resilient to extreme disturbances, with high resistance to the effects of short‐term reductions in vital rates and recovery within 20 years. Applying the general framework presented here across disturbance‐prone species and ecosystems would improve understanding of population resilience and generate specific projections of resilience that are needed for effective conservation planning.  相似文献   

9.
Endangered species worldwide exist in remnant populations, often within fragmented landscapes. Although assessment of genetic diversity in fragmented habitats is very important for conservation purposes, it is usually impossible to evaluate the amount of diversity that has actually been lost. Here, we compared population structure and levels of genetic diversity within populations of spotted suslik Spermophilus suslicus, inhabiting two different parts of the species range characterized by different levels of habitat connectivity. We used microsatellites to analyze 10 critically endangered populations located at the western part of the range, where suslik habitat have been severely devastated due to agriculture industrialization. Their genetic composition was compared with four populations from the eastern part of the range where the species still occupies habitat with reasonable levels of connectivity. In the western region, we detected extreme population structure (F ST = 0.20) and levels of genetic diversity (Allelic richness ranged from 1.45 to 3.07) characteristic for highly endangered populations. Alternatively, in the eastern region we found significantly higher allelic richness (from 5.09 to 5.81) and insignificant population structure (F ST = 0.03). As we identified a strong correlation between genetic and geographic distance and a lack of private alleles in the western region, we conclude that extreme population structure and lower genetic diversity is due to recent habitat loss. Results from this study provide guidelines for conservation and management of this highly endangered species.  相似文献   

10.
Habitat fragmentation can lead to a decline of genetic diversity, a potential risk for the survival of natural populations. Fragmented populations can become highly differentiated due to reduced gene flow and genetic drift. A decline in number of individuals can result in lower reproductive fitness due to inbreeding effects. We investigated genetic variation within and between 11 populations of the rare and endangered plant Silene chlorantha in northeastern Germany to support conservation strategies. Genetic diversity was evaluated using AFLP techniques and the results were correlated to fitness traits. Fitness evaluation in nature and in a common garden approach was conducted. Our analysis revealed population differentiation was high and within population genetic diversity was intermediate. A clear population structure was supported by a Bayesian approach, AMOVA and neighbour-joining analysis. No correlation between genetic and geographic distance was found. Our results indicate that patterns of population differentiation were mainly caused by temporal and/or spatial isolation and genetic drift. The fitness evaluation revealed that pollinator limitation and habitat quality seem, at present, to be more important to reproductive fitness than genetic diversity by itself. Populations of S. chlorantha with low genetic diversity have the potential to increase in individual number if habitat conditions improve. This was detected in a single large population in the investigation area, which was formerly affected by bottleneck effects.  相似文献   

11.
Owing to habitat loss populations of many organisms have declined and become fragmented. Vertebrate conservation strategies routinely consider genetic factors, but their importance in invertebrate populations is poorly understood. Bumblebees are important pollinators, and many species have undergone dramatic declines. As monoandrous social hymenopterans they may be particularly susceptible to inbreeding due to low effective population sizes. We study fragmented populations of a bumblebee species, on a model island system, and on mainland Great Britain where it is rare and declining. We use microsatellites to study: population genetic structuring and gene flow; the relationships between genetic diversity, population size and isolation; and frequencies of (sterile) diploid males - an indicator of inbreeding. We find significant genetic structuring (theta = 0.12) and isolation by distance. Populations > 10 km apart are all significantly differentiated, both on oceanic islands and on the mainland. Genetic diversity is reduced relative to closely related common species, and isolated populations exhibit further reductions. Of 16 populations, 10 show recent bottlenecking, and 3 show diploid male production. These results suggest that surviving populations of this rare insect suffer from inbreeding as a result of geographical isolation. Implications for the conservation of social hymenopterans are discussed.  相似文献   

12.
Little is known about how a 70% loss of native forests has affected the genetic connectivity of remnant bird populations in New Zealand. We use the common and widely distributed New Zealand Bellbird Anthornis melanura as an indicator species of population connectivity for well‐flighted birds. Using eight microsatellite loci, we identified five main genetic populations in the North Island, South Island, sub‐Antarctic Auckland Islands and two small remnant island populations adjacent to a large region of avian extirpations in northern North Island. Only one remnant island population, on a 30‐year‐old conservation reserve at Tiritiri Matangi, displayed a clear signature of recent genetic bottleneck. The 7% migration rate at Tiritiri Matangi indicates that bottlenecks can be maintained despite habitat rehabilitation, possibly through behavioural barriers to gene flow. Adjacent to the same extirpation zone, Bellbirds on the Poor Knights Islands were found to have low genetic diversity and low re‐colonization potential. Two gaps concordant with deforestation patterns separated the Kapiti Coast of southern North Island from populations to both the north and the south. In summary, we identified linked avian habitats, as well as isolated and inbred populations and suggest that Bellbirds are good re‐colonizers. We emphasize the importance of genetic studies that assess animal dispersal among newly rehabilitated habitat patches.  相似文献   

13.
Red Junglefowl (Gallus gallus) are among the few remaining ancestors of an extant domesticated livestock species, the domestic chicken, that still occur in the wild. Little is known about genetic diversity, population structure, and demography of wild Red Junglefowl in their natural habitats. Extinction threats from habitat loss or genetic alteration from domestic introgression exacerbate further the conservation status of this progenitor species. In a previous study, we reported extraordinary adaptive genetic variation in the MHC B‐locus in wild Red Junglefowl and no evidence of allelic introgression between wild and domestic chickens was observed. In this study, we characterized spatial genetic variation and population structure in naturally occurring populations of Red Junglefowl in their core distribution range in South Central Vietnam. A sample of 212 Red Junglefowl was obtained from geographically and ecologically diverse habitats across an area of 250 × 350 km. We used amplified fragment‐length polymorphism markers obtained from 431 loci to determine whether genetic diversity and population structure varies. We found that Red Junglefowl are widely distributed but form small and isolated populations. Strong spatial genetic patterns occur at both local and regional scales. At local scale, population stratification can be identified to approximately 5 km. At regional scale, we identified distinct populations of Red Junglefowl in the southern lowlands, northern highlands, and eastern coastal portions of the study area. Both local and long‐distance genetic patterns observed in wild Red Junglefowl may reflect the species’ ground‐dwelling and territorial characteristics, including dispersal barriers imposed by the Annamite Mountain Range. Spatially explicit analyses with neutral genetic markers can be highly informative and here elevates the conservation profile of the wild ancestors of domesticated chickens.  相似文献   

14.
Tiger beetles (Insecta: Coleoptera: Cicindelidae) often occupy small patches of suitable habitat in otherwise unsuitable landscapes. Such patches are easily overlooked, which may lead to underestimates of both the number of occurrences and the overall population size. In this study, simple World Wide Web-based tools (Google Earth and Microsoft Terraserver) were used to search high-resolution satellite imagery for patches of suitable habitat for globally and regionally rare tiger beetles on a 3,278 ha wildlife refuge in Maryland, USA. This tract is largely forested but contains scattered small open areas of sand and clay soils that are potential habitat for tiger beetles of conservation concern. Visual inspection of remotely sensed imagery resulted in the identification of 19 potential habitat patches, 15 of which yielded tiger beetle populations when surveyed on the ground. The number of species of tiger beetles recorded from this tract was increased from 3 to 8 and two new sites were discovered for the state sensitive species Cicindela scutellaris rugifrons Dejean. In addition, a small population of C. splendida Hentz was discovered, a species last reported from Maryland in 1948. The technique described here shows great promise for locating small patches of potential tiger beetle habitat in otherwise unsuitable landscapes.  相似文献   

15.
Appropriate management of species of conservation concern requires designing strategies that should include genetic information as small population size and restricted geographic range can reduce genetic variation. We used AFLPs to investigate genetic variation within and among populations of the endangered narrow endemic Centaurea borjae, and found no evidence for genetic impoverishment despite its <40 km range and potential for vegetative propagation. Genetic variation was comparable to other plants with similar life history (88 % occurring within populations) and potential clone mates were less frequent than expected. Nonetheless, populations separated by few hundred meters showed signs of significant genetic differentiation suggesting low gene flow between them. Our results suggested that the three geographically closer populations located at the center of the range might be treated as a single management unit, while the remaining ones could be considered independent units. We found evidence of fine-scale spatial genetic structure up to 80 m indicating that the collection of germplasm for ex-situ conservation should focus on individuals separated >80 m to maximize genetic variation.  相似文献   

16.
Two ant species, Odontomachus rixosus and Pheidole annexus, were studied in the tropical rainforests of Sabah, Malaysia, North Borneo, to analyze the impact of habitat fragmentation on the genetic diversity and population structure of ant populations using RAPD-fingerprinting. Ants were sampled in a contiguous (43,800 ha) and three patches of primary rainforests of varying size (4294, 146 and 20 ha) that were fragmented about 40 years ago. We found a decrease in genetic variability for both species in the fragmented populations compared to the contiguous. Genetic distances between populations resembled the geographical arrangement of populations and can be explained by an effect of isolation by distance. A high degree in population subdivision suggests a lack of meta-population dynamics due to a shortage of gene flow between populations, possibly the result of the high degree of habitat isolation by oil palm plantations. Although the results of this study are limited due to low replication this is the first data on genetic patterns of insect populations in fragmented rainforests and should be seen as starting point for future research. The value of small to medium sized protection areas for conservation needs to be carefully evaluated in the context of this study, as even relatively large areas (4294 ha) may not prevent the critical loss of genetic variability and guarantee long-term survival of organisms.  相似文献   

17.
There is no general explanation for why species have restricted geographic distributions. One hypothesis posits that range expansion or increasing scarcity of suitable habitat results in accumulation of mutational load due to enhanced genetic drift, which constrains population performance toward range limits and further expansion. We tested this hypothesis in the North American plant, Arabidopsis lyrata. We experimentally assessed mutational load by crossing plants of 20 populations from across the entire species range and by raising the offspring of within- and between-population crosses at five common garden sites within and beyond the range. Offspring performance was tracked over three growing seasons. The heterosis effect, depicting expressed mutational load, was increased in populations with heightened genomic estimates of load, longer expansion distance or long-term isolation, and a selfing mating system. The decline in performance of within-population crosses amounted to 80%. Mutation accumulation due to past range expansion and long-term isolation of populations in the area of range margins is therefore a strong determinant of population-mean performance, and the magnitude of effect may be sufficient to cause range limits.  相似文献   

18.
There is widespread concern regarding the impacts of anthropogenic activities on connectivity among populations of plants and animals, and understanding how contemporary and historical processes shape metapopulation dynamics is crucial for setting appropriate conservation targets. We used genetic data to identify population clusters and quantify gene flow over historical and contemporary time frames in the Diamondback Terrapin (Malaclemys terrapin). This species has a long and complicated history with humans, including commercial overharvesting and subsequent translocation events during the early twentieth century. Today, terrapins face threats from habitat loss and mortality in fisheries bycatch. To evaluate population structure and gene flow among Diamondback Terrapin populations in the Chesapeake Bay region, we sampled 617 individuals from 15 localities and screened individuals at 12 polymorphic microsatellite loci. Our goals were to demarcate metapopulation structure, quantify genetic diversity, estimate effective population sizes, and document temporal changes in gene flow. We found that terrapins in the Chesapeake Bay region harbour high levels of genetic diversity and form four populations. Effective population sizes were variable. Among most population comparisons, estimates of historical and contemporary terrapin gene flow were generally low (m ≈ 0.01). However, we detected a substantial increase in contemporary gene flow into Chesapeake Bay from populations outside the bay, as well as between two populations within Chesapeake Bay, possibly as a consequence of translocations during the early twentieth century. Our study shows that inferences across multiple time scales are needed to evaluate population connectivity, especially as recent changes may identify threats to population persistence.  相似文献   

19.
Dispersal is crucial for gene flow and often determines the long‐term stability of meta‐populations, particularly in rare species with specialized life cycles. Such species are often foci of conservation efforts because they suffer disproportionally from degradation and fragmentation of their habitat. However, detailed knowledge of effective gene flow through dispersal is often missing, so that conservation strategies have to be based on mark–recapture observations that are suspected to be poor predictors of long‐distance dispersal. These constraints have been especially severe in the study of butterfly populations, where microsatellite markers have been difficult to develop. We used eight microsatellite markers to analyse genetic population structure of the Large Blue butterfly Maculinea arion in Sweden. During recent decades, this species has become an icon of insect conservation after massive decline throughout Europe and extinction in Britain followed by reintroduction of a seed population from the Swedish island of Öland. We find that populations are highly structured genetically, but that gene flow occurs over distances 15 times longer than the maximum distance recorded from mark–recapture studies, which can only be explained by maximum dispersal distances at least twice as large as previously accepted. However, we also find evidence that gaps between sites with suitable habitat exceeding ~20 km induce genetic erosion that can be detected from bottleneck analyses. Although further work is needed, our results suggest that M. arion can maintain fully functional metapopulations when they consist of optimal habitat patches that are no further apart than ~10 km.  相似文献   

20.
Golden‐headed lion tamarins (GHLTs; Leontopithecus chrysomelas) are endangered primates endemic to the Brazilian Atlantic Forest, where loss of forest and its connectivity threaten species survival. Understanding the role of habitat availability and configuration on population declines is critical for guiding proactive conservation for this, and other, endangered species. We conducted population viability analysis to assess vulnerability of ten GHLT metapopulations to habitat loss and small population size. Seven metapopulations had a low risk of extirpation (or local extinction) over the next 100 years assuming no further forest loss, and even small populations could persist with immediate protection. Three metapopulations had a moderate/high risk of extirpation, suggesting extinction debt may be evident in parts of the species’ range. When deforestation was assumed to continue at current rates, extirpation risk significantly increased while abundance and genetic diversity decreased for all metapopulations. Extirpation risk was significantly negatively correlated with the size of the largest patch available to metapopulations, underscoring the importance of large habitat patches for species persistence. Finally, we conducted sensitivity analysis using logistic regression, and our results showed that local extinction risk was sensitive to percentage of females breeding, adult female mortality, and dispersal rate and survival; conservation or research programs that target these aspects of the species’ biology/ecology could have a disproportionately important impact on species survival. We stress that efforts to protect populations and tracts of habitat of sufficient size throughout the species’ distribution will be important in the near‐term to protect the species from continuing decline and extinction.  相似文献   

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