Landscape structure and the genetic effects of a population collapse

Both landscape structure and population size fluctuations influence population genetics. While independent effects of these factors on genetic patterns and processes are well studied, a key challenge is to understand their interaction, as populations are simultaneously exposed to habitat fragmentation and climatic changes that increase variability in population size. In a population network of an alpine butterfly, abundance declined 60–100% in 2003 because of low over-winter survival. Across the network, mean microsatellite genetic diversity did not change. However, patch connectivity and local severity of the collapse interacted to determine allelic richness change within populations, indicating that patch connectivity can mediate genetic response to a demographic collapse. The collapse strongly affected spatial genetic structure, leading to a breakdown of isolation-by-distance and loss of landscape genetic pattern. Our study reveals important interactions between landscape structure and temporal demographic variability on the genetic diversity and genetic differentiation of populations. Projected future changes to both landscape and climate may lead to loss of genetic variability from the studied populations, and selection acting on adaptive variation will likely occur within the context of an increasing influence of genetic drift.     

Agricultural intensification alters marbled newt genetic diversity and gene flow through density and dispersal reduction

Recent agricultural intensification threatens global biodiversity with amphibians being one of the most impacted groups. Because of their biphasic life cycle, amphibians are particularly vulnerable to habitat loss and fragmentation that often result in small, isolated populations and loss of genetic diversity. Here, we studied how landscape heterogeneity affects genetic diversity, gene flow and demographic parameters in the marbled newt, Triturus marmoratus, over a hedgerow network landscape in Western France. While the northern part of the study area consists of preserved hedged farmland, the southern part was more profoundly converted for intensive arable crops production after WWII. Based on 67 sampled ponds and 10 microsatellite loci, we characterized regional population genetic structure and evaluated the correlation between landscape variables and (i) local genetic diversity using mixed models and (ii) genetic distance using multiple regression methods and commonality analysis. We identified a single genetic population characterized by a spatially heterogeneous isolation-by-distance pattern. Pond density in the surrounding landscape positively affected local genetic diversity while arable crop land cover negatively affected gene flow and connectivity. We used demographic inferences to quantitatively assess differences in effective population density and dispersal between the contrasted landscapes characterizing the northern and southern parts of the study area. Altogether, results suggest recent land conversion affected T. marmoratus through reduction in both effective population density and dispersal due to habitat loss and reduced connectivity.     

Characterizing the post‐recolonization of Antechinus flavipes and its genetic implications in a production forest landscape

Production landscapes, where activities such as timber harvesting, grazing, and resource extraction take place, have considerably reduced the extent of natural habitats. The ecological restoration of these landscapes is, in many cases, the best remaining option to protect biodiversity. However, it is unclear whether restoration designed to avert biodiversity loss in restored landscapes can also maintain genetic diversity in recolonizing faunal populations. We employed core concepts in the field of population genetics to address questions of genetic diversity and gene flow in recolonizing faunal populations, using a small and vagile marsupial (Antechinus flavipes) inhabiting a mined landscape under restoration. We did not detect a disruption of gene flow that led to genetic substructuring, suggesting adequate levels of gene flow across the landscape. Parameters of neutral genetic diversity were high in groups of individuals sampled in both restored and unmined sites. Our results are encouraging as they indicate that ecological restoration has the potential to not just increase available habitat, but also to maintain genetic diversity. However, there is evidence that past anthropogenic disturbances affected the genetics of the population at the regional level. Although restoration at the local level may seem to be successful, it is necessary to manage populations at larger spatial scales than where restoration is conducted, and over long temporal scales, if genetic diversity is to be maintained in restored landscapes. The field of population genetics is an underused tool in ecological restoration yet can provide important insights into how well restoration achieves its goals.     

Landscape-level comparison of genetic diversity and differentiation in a small mammal inhabiting different fragmented landscapes of the Brazilian Atlantic Forest

Habitat loss and fragmentation can have detrimental effects on all levels of biodiversity, including genetic variation. Most studies that investigate genetic effects of habitat loss and fragmentation focus on analysing genetic data from a single landscape. However, our understanding of habitat loss effects on landscape-wide patterns of biodiversity would benefit from studies that are based on quantitative comparisons among multiple study landscapes. Here, we use such a landscape-level study design to compare genetic variation in the forest-specialist marsupial Marmosops incanus from four 10,000-hectare Atlantic forest landscapes which differ in the amount of their remaining native forest cover (86, 49, 31, 11 %). Additionally, we used a model selection framework to evaluate the influence of patch characteristics on genetic variation within each landscape. We genotyped 529 individuals with 12 microsatellites to statistically compare estimates of genetic diversity and genetic differentiation in populations inhabiting different forest patches within the landscapes. Our study indicates that before the extinction of the specialist species (here in the 11 % landscape) genetic diversity is significantly reduced in the 31 % landscape, while genetic differentiation is significantly higher in the 49 and 31 % landscapes compared to the 86 % landscape. Results further provide evidence for non-proportional responses of genetic diversity and differentiation to increasing habitat loss, and suggest that local patch isolation impacts gene flow and genetic connectivity only in the 31 % landscape. These results have high relevance for analysing landscape genetic relationships and emphasize the importance of landscape-level study designs for understanding habitat loss effects on all levels of biodiversity.     

Water availability strongly impacts population genetic patterns of an imperiled Great Plains endemic fish

Genetic, demographic, and environmental processes affect natural populations synergistically, and understanding their interplay is crucial for the conservation of biodiversity. Stream fishes in metapopulations are particularly sensitive to habitat fragmentation because persistence depends on dispersal and colonization of new habitat but dispersal is constrained to stream networks. Great Plains streams are increasingly fragmented by water diversion and climate change, threatening connectivity of fish populations in this ecosystem. We used seven microsatellite loci to describe population and landscape genetic patterns across 614 individuals from 12 remaining populations of Arkansas darter (Etheostoma cragini) in Colorado, a candidate species for listing under the U.S. Endangered Species Act. We found small effective population sizes, low levels of genetic diversity within populations, and high levels of genetic structure, especially among basins. Both at- and between-site landscape features were associated with genetic diversity and connectivity, respectively. Available stream habitat and amount of continuous wetted area were positively associated with genetic diversity within a site, while stream distance and intermittency were the best predictors of genetic divergence among sites. We found little genetic contribution from historic supplementation efforts, and we provide a set of management recommendations for this species that incorporate a conservation genetics perspective.     

Fine-scale spatial genetic structure and dispersal among spotted salamander (Ambystoma maculatum) breeding populations

We examined fine-scale genetic variation among breeding aggregations of the spotted salamander (Ambystoma maculatum) to quantify dispersal, interpopulation connectivity and population genetic structure. Spotted salamanders rely on temporary ponds or wetlands for aggregate breeding. Adequate breeding sites are relatively isolated from one another and field studies suggest considerable adult site fidelity; therefore, we expected to find population structure and differentiation at small spatial scales. We used microsatellites to estimate population structure and dispersal among 29 breeding aggregations in Tompkins County, New York, USA, an area encompassing 1272 km(2). Bayesian and frequency-based analyses revealed fine-scale genetic structure with two genetically defined demes: the North deme included seven breeding ponds, and the South deme included 13 ponds. Nine ponds showed evidence of admixture between these two genetic pools. Bayesian assignment tests for detection of interpopulation dispersal indicate that immigration among ponds is common within demes, and that certain populations serve as sources of immigrants to neighbouring ponds. Likewise, spatial genetic correlation analyses showed that populations < or = 4.8 km distant from each other show significant genetic correlation that is not evident at higher scales. Within-population levels of relatedness are consistently larger than expected if mating were completely random across ponds, and in the case of a few ponds, within-population processes such as inbreeding or reproductive skew contribute significantly to differentiation from neighbouring ponds. Our data underscore the importance of these within-population processes as a source of genetic diversity across the landscape, despite considerable population connectivity. Our data further suggest that spotted salamander breeding groups behave as metapopulations, with population clusters as functional units, but sufficient migration among demes to allow for potential rescue and recolonization. Amphibian habitats are becoming increasingly fragmented and a clear understanding of dispersal and patterns of population connectivity for taxa with different ecologies and life histories is crucial for their conservation.     

宏生态尺度上景观破碎化对物种丰富度的影响

生物多样性的地理格局及其形成机制是宏生态学与生物地理学的研究热点。大量研究表明,景观尺度上的生境破碎化对物种多样性的分布格局具有重要作用,但目前尚不清楚这种作用是否足以在宏生态尺度上对生物多样性地理格局产生显著影响。利用中国大陆鸟类和哺乳动物的物种分布数据,在100 km×100 km网格的基础上生成了这两个类群生物的物种丰富度地理格局,进一步利用普通最小二乘法模型和空间自回归模型研究了物种丰富度与气候、生境异质性、景观破碎化的相关关系。结果表明,景观破碎化因子与鸟类和哺乳动物的物种丰富度都具有显著的关联关系,其方差贡献率可达约30%—50%(非空间模型)和60%—80%(空间模型),略低于或接近于气候和生境异质性因子。方差分解结果显示,景观破碎化因子与气候和生境异质性因子的方差贡献率的重叠部分达20%—40%。相对鸟类而言,景观破碎化对哺乳动物物种丰富度的地理格局具有更高的解释率。     

Connectivity and gene flow among Eastern Tiger Salamander (Ambystoma tigrinum) populations in highly modified anthropogenic landscapes

Fragmented landscapes resulting from anthropogenic habitat modification can have significant impacts on dispersal, gene flow, and persistence of wildlife populations. Therefore, quantifying population connectivity across a mosaic of habitats in highly modified landscapes is critical for the development of conservation management plans for threatened populations. Endangered populations of the eastern tiger salamander (Ambystoma tigrinum) in New York and New Jersey are at the northern edge of the species’ range and remaining populations persist in highly developed landscapes in both states. We used landscape genetic approaches to examine regional genetic population structure and potential barriers to migration among remaining populations. Despite the post-glacial demographic processes that have shaped genetic diversity in tiger salamander populations at the northern extent of their range, we found that populations in each state belong to distinct genetic clusters, consistent with the large geographic distance that separates them. We detected overall low genetic diversity and high relatedness within populations, likely due to recent range expansion, isolation, and relatively small population sizes. Nonetheless, landscape connectivity analyses reveal habitat corridors among remaining breeding ponds. Furthermore, molecular estimates of population connectivity among ponds indicate that gene flow still occurs at regional scales. Further fragmentation of remaining habitat will potentially restrict dispersal among breeding ponds, cause the erosion of genetic diversity, and exacerbate already high levels of inbreeding. We recommend the continued management and maintenance of habitat corridors to ensure long-term viability of these endangered populations.     

Differential effects of spatial network structure and scale on population size and genetic diversity of the ninespine stickleback in a remnant wetland system

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基于景观遗传学的滇金丝猴栖息地连接度分析

结合景观遗传学,应用最小费用距离模型对物种栖息地进行连接度分析,能够为生物多样性保护和自然保护区管理提供更加真实准确及可实践操作的指导。选取滇金丝猴这一珍稀濒危物种,结合景观遗传学,应用最小费用距离模型对其栖息地进行了连接度和潜在扩散廊道分析。并且通过连接度的分析和制图绘制出了更为准确的种群间潜在扩散廊道,确定了受人工障碍影响的廊道及敏感区域。结果表明,研究区内的5个亚群中,仅S3亚群内的5个猴群保持着较好的连接度,总体来说,各亚群内的连接度相对于各亚群间连接度保持的较好。除S3亚群中猴群间的潜在扩散廊道较为理想外,其余种群间的潜在扩散廊道均受人工斑块的影响,多数廊道被人工障碍阻断,或面临即将被阻断的情况,对于滇金丝猴的扩散交流影响较大。敏感区域多集中在中南部的3个亚群间,这些敏感区域应作为景观恢复及保护区规划的重要优先区域。     

sGD: software for estimating spatially explicit indices of genetic diversity

Anthropogenic landscape changes have greatly reduced the population size, range and migration rates of many terrestrial species. The small local effective population size of remnant populations favours loss of genetic diversity leading to reduced fitness and adaptive potential, and thus ultimately greater extinction risk. Accurately quantifying genetic diversity is therefore crucial to assessing the viability of small populations. Diversity indices are typically calculated from the multilocus genotypes of all individuals sampled within discretely defined habitat patches or larger regional extents. Importantly, discrete population approaches do not capture the clinal nature of populations genetically isolated by distance or landscape resistance. Here, we introduce spatial Genetic Diversity (sGD), a new spatially explicit tool to estimate genetic diversity based on grouping individuals into potentially overlapping genetic neighbourhoods that match the population structure, whether discrete or clinal. We compared the estimates and patterns of genetic diversity using patch or regional sampling and sGD on both simulated and empirical populations. When the population did not meet the assumptions of an island model, we found that patch and regional sampling generally overestimated local heterozygosity, inbreeding and allelic diversity. Moreover, sGD revealed fine-scale spatial heterogeneity in genetic diversity that was not evident with patch or regional sampling. These advantages should provide a more robust means to evaluate the potential for genetic factors to influence the viability of clinal populations and guide appropriate conservation plans.     

Anuran abundance and persistence in agricultural landscapes during a climatic extreme

Climate change in concert with habitat loss and degradation are major threats to global biodiversity. As part of climate change, the occurrence of extreme climatic events is expected to increase. Agricultural intensification has led to the increased homogeneity of agricultural habitats and declines in farmland species diversity. We investigated the abundance of common frog Rana temporaria populations in boreal farmlands in relation to multiple scales of landscape structure during years 2002–2003, and the effect of habitat structure on R. temporaria population persistence during a severe drought. On average, 113 and 24 egg clutches were observed per site in years 2002 and 2003, respectively. This dramatic decline was synchronized over the entire study area (ca. 320 km²), with some local variations. Population persistence was higher in sites where ground water levels decreased less but it was also positively correlated with the heterogeneity of the adjacent landscape. Under normal weather conditions, local habitat characteristics had a dominating role on R. temporaria population abundance, as it was positively correlated with the amount of ditches and ponds within the study sites. After the drought, however, population abundance was related to landscape and regional level factors. The results indicate that landscape homogenization can have negative effects on population persistence during climate change. They also show that the scale at which landscape characteristics affect populations can be strongly dependent of processes functioning at large scales, such as weather. In summary, heterogeneous landscapes may lower the risk of regional amphibian population declines under extreme weather perturbations and serve as sources of recovery in postdisturbance recovery phases. Thus, maintaining such areas should be promoted in long-term biodiversity conservation.     

Multiple-scaled spatial genetic structures of <Emphasis Type="Italic">Fraxinus mandshurica</Emphasis> over a riparian–mountain landscape in Northeast China

Landscape genetics increasingly focuses on the way in which landscape features cause the fragmentation of lineages of terrestrial organisms. However, landscape features can also provide functional connectivity or corridors, enhancing the dispersal of plant populations, particularly the case in riparian habitat. Unfortunately, recent research in tree genetics has paid little attention to this role. To examine the possible effects of landscape connectivity on the current population genetic distribution of Fraxinus mandshurica and to provide insights into conserving the local genetic diversity for this endangered tree species, we used nine nuclear microsatellite loci to examine the spatial genetic structure of F. mandshurica at multiple-scales over a riparian–mountain landscape in Northeast China. F-statistics indicated that the magnitude of among-population genetic differentiation was significantly higher between the riparian and mountain habitats than within the riparian habitat. Spatial analysis of molecular variance and principal coordinate analysis consistently revealed that this species exhibited a clear landscape genetic structure between the riparian and mountain habitats, despite no significant isolation by distance pattern being identified by the Mantel test. Spatial autocorrelation analysis further demonstrated significant, positive fine-scale spatial genetic structure among individuals over short distances (<80 m) in each mountain population. Conversely, no spatial genetic structures were identified within and among the riparian populations. Overall, the results suggest that seed dispersal is very low among mountain populations; however seed transport is probably enhanced by a secondary phase of hydrochory (water-dispersal) among riparian populations during flooding. Despite this, there was no significant accumulation of genetic diversity in downstream populations along the main channel. This result suggests that hydrochory is not sufficient to produce a clear unidirectional gene flow along the water course, although it may impede the development of spatial genetic structuring within and among riparian populations.     

景观历史对物种多样性的影响: 以内蒙古伊敏露天煤矿为例

矿产开采等人类活动极大地改变着生态环境和景观格局, 景观变化又是导致区域和全球物种多样性丧失的主要原因之一。然而, 物种多样性对周边景观变化响应的时间尺度问题往往被人们忽略。作者以内蒙古草原区伊敏露天煤矿为例, 从物种和功能群两个层次上, 探讨了不同的空间范围(1 km、2 km、3 km、4 km、6 km、8 km、10 km)内在不同时期(1975年、1990年、2000年、2010年)的景观格局(景观优势度指数、生境综合连接度指数和生境连接度概率指数)与生物多样性之间的关系。结果显示: 当前物种多样性与开矿前和开矿初期周边景观格局之间的相关性更高, 而且与4–8 km缓冲区范围内景观格局之间的关系更加密切。不同功能群物种丰富度与景观格局之间的关系不同, 其中, 多年生根茎禾草物种丰富度和当前小尺度(1–3 km)景观格局之间呈显著相关; 多年生杂类草和开矿前和开矿初期大尺度(4–10 km)景观格局之间相关显著; 多年生丛生禾草与景观格局的相关性并未达到显著水平, 但是随着空间尺度的增加出现单峰趋势, 在6 km范围上最高; 灌木、半灌木与景观格局的相关关系随着空间尺度的增加而增加; 一二年生草本与景观格局的相关性始终最低。为此, 本文得出如下结论: (1)物种多样性对周边景观格局变化的响应存在一定时间的滞后, 人类当前不合理的土地利用方式可能引起未来一段时间内该地区一些物种的消失; (2)区域种库决定小尺度物种多样性的大小, 研究区4–8 km范围内具有连通性的生境斑块是主要的种库资源; (3)植物的繁殖策略及种子传播方式是破碎化生境中物种多样性维持的重要机制。     

Patterns of genetic variability and habitat occupancy in Crepis triasii (Asteraceae) at different spatial scales: insights on evolutionary processes leading to diversification in continental islands

Background and Aims

Archipelagos are unique systems for studying evolutionary processes promoting diversification and speciation. The islands of the Mediterranean basin are major areas of plant richness, including a high proportion of narrow endemics. Many endemic plants are currently found in rocky habitats, showing varying patterns of habitat occupancy at different spatial scales throughout their range. The aim of the present study was to understand the impact of varying patterns of population distribution on genetic diversity and structure to shed light on demographic and evolutionary processes leading to population diversification in Crepis triasii, an endemic plant from the eastern Balearic Islands.

Methods

Using allozyme and chloroplast markers, we related patterns of genetic structure and diversity to those of habitat occupancy at a regional (between islands and among populations within islands) and landscape (population size and connectivity) scale.

Key Results

Genetic diversity was highly structured both at the regional and at the landscape level, and was positively correlated with population connectivity in the landscape. Populations located in small isolated mountains and coastal areas, with restricted patterns of regional occupancy, were genetically less diverse and much more differentiated. In addition, more isolated populations had stronger fine-scale genetic structure than well-connected ones. Changes in habitat availability and quality arising from marine transgressions during the Quaternary, as well as progressive fragmentation associated with the aridification of the climate since the last glaciation, are the most plausible factors leading to the observed patterns of genetic diversity and structure.

Conclusions

Our results emphasize the importance of gene flow in preventing genetic erosion and maintaining the evolutionary potential of populations. They also agree with recent studies highlighting the importance of restricted gene flow and genetic drift as drivers of plant evolution in Mediterranean continental islands.     

Impact of cyclones on hard coral and metapopulation structure,connectivity and genetic diversity of coral reef fish

Cyclones have one of the greatest effects on the biodiversity of coral reefs and the associated species. But it is unknown how stochastic alterations in habitat structure influence metapopulation structure, connectivity and genetic diversity. From 1993 to 2018, the reefs of the Capricorn Bunker Reef group in the southern part of the Great Barrier Reef were impacted by three tropical cyclones including cyclone Hamish (2009, category 5). This resulted in substantial loss of live habitat-forming coral and coral reef fish communities. Within 6–8 years after cyclones had devastated, live hard corals recovered by 50–60%. We show the relationship between hard coral cover and the abundance of the neon damselfish (Pomacentrus coelestis), the first fish colonizing destroyed reefs. We present the first long-term (2008–2015 years corresponding to 16–24 generations of P. coelestis) population genetic study to understand the impact of cyclones on the meta-population structure, connectivity and genetic diversity of the neon damselfish. After the cyclone, we observed the largest change in the genetic structure at reef populations compared to other years. Simultaneously, allelic richness of genetic microsatellite markers dropped indicating a great loss of genetic diversity, which increased again in subsequent years. Over years, metapopulation dynamics were characterized by high connectivity among fish populations associated with the Capricorn Bunker reefs (2200 km²); however, despite high exchange, genetic patchiness was observed with annual strong genetic divergence between populations among reefs. Some broad similarities in the genetic structure in 2015 could be explained by dispersal from a source reef and the related expansion of local populations. This study has shown that alternating cyclone-driven changes and subsequent recovery phases of coral habitat can greatly influence patterns of reef fish connectivity. The frequency of disturbances determines abundance of fish and genetic diversity within species.

     

Within-river gene flow in the hellbender (Cryptobranchus alleganiensis) and implications for restorative release

Understanding how populations are genetically and demographically connected is beneficial for species management, since gene flow and dispersal contribute to genetic diversity and population persistence. For hellbenders (Cryptobranchus alleganiensis), an aquatic salamander species experiencing dramatic declines in population size, fine-scale (i.e. within river) patterns of genetic diversity and gene flow are not well understood. Previous findings indicate that hellbenders are habitat specialists that exhibit extreme site fidelity and low vagility, suggesting that gene flow is restricted among the several, discrete habitat patches within a river. Using 15 polymorphic microsatellite loci and 497 hellbender samples from four Missouri rivers, we assessed fine-scale patterns of genetic diversity in order to infer population connectivity and aid in population management. Results indicate moderate levels of genetic variation (H_O = 0.66–0.78) with little differentiation among habitat patches (avg. F_ST = 0.002) and no evidence of isolation by distance. Our data suggest that hellbender gene flow has been extensive even among habitat patches separated by distances greater than >100 km. These results are useful for hellbender management, especially in terms of making informed decisions regarding restorative releases of captively propagated individuals.     

Population structure and landscape genetics in the endangered subterranean rodent Ctenomys porteousi

In order to devise adequate conservation and management strategies for endangered species, it is important to incorporate a reliable understanding of its spatial population structure, detecting the existence of demographic partitions throughout its geographical range and characterizing the distribution of its genetic diversity. Moreover, in species that occupy fragmented habitats it is essential to know how landscape characteristics may affect the genetic connectivity among populations. In this study we use eight microsatellite markers to analyze population structure and gene flow patterns in the complete geographic range of the endangered rodent Ctenomys porteousi. Also, we use landscape genetics approaches to evaluate the effects of landscape configuration on the genetic connectivity among populations. In spite of geographical proximity of the sampling sites (8–27 km between the nearest sites) and the absence of marked barriers to individual movement, strong population structure and low values of gene flow were observed. Genetic differentiation among sampling sites was consistent with a simple model of isolation by distance, where peripheral areas showed higher population differentiation than those sites located in the central area of the species’ distribution. Landscape genetics analysis suggested that habitat fragmentation at regional level has affected the distribution of genetic variation among populations. The distance of sampling sites to areas of the landscape having higher habitat connectivity was the environmental factor most strongly related to population genetic structure. In general, our results indicate strong genetic structure in C. porteousi, even at a small spatial scale, and suggest that habitat fragmentation could increase the population differentiation.     

Habitat fragmentation in coastal southern California disrupts genetic connectivity in the cactus wren (Campylorhynchus brunneicapillus)

Achieving long‐term persistence of species in urbanized landscapes requires characterizing population genetic structure to understand and manage the effects of anthropogenic disturbance on connectivity. Urbanization over the past century in coastal southern California has caused both precipitous loss of coastal sage scrub habitat and declines in populations of the cactus wren (Campylorhynchus brunneicapillus). Using 22 microsatellite loci, we found that remnant cactus wren aggregations in coastal southern California comprised 20 populations based on strict exact tests for population differentiation, and 12 genetic clusters with hierarchical Bayesian clustering analyses. Genetic structure patterns largely mirrored underlying habitat availability, with cluster and population boundaries coinciding with fragmentation caused primarily by urbanization. Using a habitat model we developed, we detected stronger associations between habitat‐based distances and genetic distances than Euclidean geographic distance. Within populations, we detected a positive association between available local habitat and allelic richness and a negative association with relatedness. Isolation‐by‐distance patterns varied over the study area, which we attribute to temporal differences in anthropogenic landscape development. We also found that genetic bottleneck signals were associated with wildfire frequency. These results indicate that habitat fragmentation and alterations have reduced genetic connectivity and diversity of cactus wren populations in coastal southern California. Management efforts focused on improving connectivity among remaining populations may help to ensure population persistence.