Habitat barriers limit gene flow and illuminate historical events in a wide-ranging carnivore, the American puma

We examined the effects of habitat discontinuities on gene flow among puma (Puma concolor) populations across the southwestern USA. Using 16 microsatellite loci, we genotyped 540 pumas sampled throughout the states of Utah, Colorado, Arizona, and New Mexico, where a high degree of habitat heterogeneity provides for a wide range of connective habitat configurations between subpopulations. We investigated genetic structuring using complementary individual- and population-based analyses, the latter employing a novel technique to geographically cluster individuals without introducing investigator bias. The analyses revealed genetic structuring at two distinct scales. First, strikingly strong differentiation between northern and southern regions within the study area suggests little migration between them. Second, within each region, gene flow appears to be strongly limited by distance, particularly in the presence of habitat barriers such as open desert and grasslands. Northern pumas showed both reduced genetic diversity and greater divergence from a hypothetical ancestral population based on Bayesian clustering analyses, possibly reflecting a post-Pleistocene range expansion. Bayesian clustering results were sensitive to sampling density, which may complicate inference of numbers of populations when using this method. The results presented here build on those of previous studies, and begin to complete a picture of how different habitat types facilitate or impede gene flow among puma populations.     

Anthropogenic Habitats Facilitate Dispersal of an Early Successional Obligate: Implications for Restoration of an Endangered Ecosystem

Landscape modification and habitat fragmentation disrupt the connectivity of natural landscapes, with major consequences for biodiversity. Species that require patchily distributed habitats, such as those that specialize on early successional ecosystems, must disperse through a landscape matrix with unsuitable habitat types. We evaluated landscape effects on dispersal of an early successional obligate, the New England cottontail (Sylvilagus transitionalis). Using a landscape genetics approach, we identified barriers and facilitators of gene flow and connectivity corridors for a population of cottontails in the northeastern United States. We modeled dispersal in relation to landscape structure and composition and tested hypotheses about the influence of habitat fragmentation on gene flow. Anthropogenic and natural shrubland habitats facilitated gene flow, while the remainder of the matrix, particularly development and forest, impeded gene flow. The relative influence of matrix habitats differed between study areas in relation to a fragmentation gradient. Barrier features had higher explanatory power in the more fragmented site, while facilitating features were important in the less fragmented site. Landscape models that included a simultaneous barrier and facilitating effect of roads had higher explanatory power than models that considered either effect separately, supporting the hypothesis that roads act as both barriers and facilitators at all spatial scales. The inclusion of LiDAR-identified shrubland habitat improved the fit of our facilitator models. Corridor analyses using circuit and least cost path approaches revealed the importance of anthropogenic, linear features for restoring connectivity between the study areas. In fragmented landscapes, human-modified habitats may enhance functional connectivity by providing suitable dispersal conduits for early successional specialists.     

Habitat Use by Sympatric Jaguars and Pumas Across a Gradient of Human Disturbance in Belize

Jaguars (Panthera onca) and pumas (Puma concolor) are sympatric across the entire jaguar range, where they coexist in increasingly fragmented landscapes under threat of persecution mainly in response to livestock predation. Pumas are known to inhabit a greater variety of natural habitats than jaguars, but little is known about the influence of anthropogenic factors on the coexistence of these two similar-sized cats. This study compares habitat use of jaguars and pumas in Belize, Central America, using 1380 jaguar and puma photo captures from 3 yr of camera trapping, comprising 64–74 individual jaguars and an unknown number of pumas. Jaguars and pumas did not differ in their use of a large block of relatively homogenous secondary rain forest. However, pumas were scarce outside this forest block, whereas jaguars were detected throughout the human-influenced landscape. Reasons for this discrepancy may include differential tolerance to human disturbance, and resource limitation for pumas outside the forest block. Intra-specific variation in jaguar activity in the form of sex-dependent habitat use was detected across the landscape. Male jaguars were detected at more locations than female jaguars and more frequently at each location, with a declining difference from a 50-fold greater detection in the protected forest, through forest buffer, savannah, pastures, to negligible difference in the disturbed forest.     

Trait-Specific Responses of Wild Bee Communities to Landscape Composition,Configuration and Local Factors

Land-use intensification and loss of semi-natural habitats have induced a severe decline of bee diversity in agricultural landscapes. Semi-natural habitats like calcareous grasslands are among the most important bee habitats in central Europe, but they are threatened by decreasing habitat area and quality, and by homogenization of the surrounding landscape affecting both landscape composition and configuration. In this study we tested the importance of habitat area, quality and connectivity as well as landscape composition and configuration on wild bees in calcareous grasslands. We made detailed trait-specific analyses as bees with different traits might differ in their response to the tested factors. Species richness and abundance of wild bees were surveyed on 23 calcareous grassland patches in Southern Germany with independent gradients in local and landscape factors. Total wild bee richness was positively affected by complex landscape configuration, large habitat area and high habitat quality (i.e. steep slopes). Cuckoo bee richness was positively affected by complex landscape configuration and large habitat area whereas habitat specialists were only affected by the local factors habitat area and habitat quality. Small social generalists were positively influenced by habitat area whereas large social generalists (bumblebees) were positively affected by landscape composition (high percentage of semi-natural habitats). Our results emphasize a strong dependence of habitat specialists on local habitat characteristics, whereas cuckoo bees and bumblebees are more likely affected by the surrounding landscape. We conclude that a combination of large high-quality patches and heterogeneous landscapes maintains high bee species richness and communities with diverse trait composition. Such diverse communities might stabilize pollination services provided to crops and wild plants on local and landscape scales.     

Importance of estimating matrix quality for modeling species distribution in complex tropical landscapes: a test with Atlantic forest small mammals

Information to guide decision making is especially urgent in human dominated landscapes in the tropics, where urban and agricultural frontiers are still expanding in an unplanned manner. Nevertheless, most studies that have investigated the influence of landscape structure on species distribution have not considered the heterogeneity of altered habitats of the matrix, which is usually high in human dominated landscapes. Using the distribution of small mammals in forest remnants and in the four main altered habitats in an Atlantic forest landscape, we investigated 1) how explanatory power of models describing species distribution in forest remnants varies between landscape structure variables that do or do not incorporate matrix quality and 2) the importance of spatial scale for analyzing the influence of landscape structure. We used standardized sampling in remnants and altered habitats to generate two indices of habitat quality, corresponding to the abundance and to the occurrence of small mammals. For each remnant, we calculated habitat quantity and connectivity in different spatial scales, considering or not the quality of surrounding habitats. The incorporation of matrix quality increased model explanatory power across all spatial scales for half the species that occurred in the matrix, but only when taking into account the distance between habitat patches (connectivity). These connectivity models were also less affected by spatial scale than habitat quantity models. The few consistent responses to the variation in spatial scales indicate that despite their small size, small mammals perceive landscape features at large spatial scales. Matrix quality index corresponding to species occurrence presented a better or similar performance compared to that of species abundance. Results indicate the importance of the matrix for the dynamics of fragmented landscapes and suggest that relatively simple indices can improve our understanding of species distribution, and could be applied in modeling, monitoring and managing complex tropical landscapes.     

Assessment of Habitat Fragmentation and Corridors for an Isolated Subspecies of the Sichuan Golden Snub-Nosed Monkey, <Emphasis Type="Italic">Rhinopithecus roxellana hubeiensis</Emphasis>

Understanding habitat quality and landscape connectivity and exploring corridors connecting habitat patches are crucial for conservation, particularly for species distributed among isolated populations. The Sichuan golden snub-nosed monkey, Rhinopithecus roxellana, is an Endangered primate species endemic to mountainous forests in China. Its easternmost distribution lies in the Shennongjia area, which harbors an isolated subspecies, R. roxellana hubeiensis. Unfortunately, it has experienced significant habitat loss, fragmentation, and dramatic population decline in recent decades, primarily due to increased human disturbance. To quantify habitat quality, identify suitable habitat patches, and detect possible linkages among these patches for R. roxellana hubeiensis, we conducted habitat suitability assessments and landscape connectivity analyses in the Shennongjia area based on a set of environmental factors. We created a habitat quality model and a movement cost surface for the Shennongjia area based on a habitat suitability index, graph theory, expert knowledge, field experience, and information from the literature. Our results show that suitable habitat for R. roxellana hubeiensis in Shennongjia is fragmented and limited, and that this is particularly true for highly suitable habitats. We detected six core habitat patches and six least-cost paths and corridors. Our study does not provide accurate distributions of the monkeys and their habitat use. However, it identifies the most feasible and traversable habitats and corridors, which should be conservation priorities for this subspecies, and provides valuable guidance for reevaluating habitat conservation plans.     

基于生境斑块的滇金丝猴景观连接度分析

基于生境斑块,结合最小费用距离并运用图论法对滇金丝猴分布区进行栖息地连接度分析,研究利用猴群的现实分布结合Logistic回归模型确定了景观功能连接的最佳距离阈值,对于功能畅通的组分,以景观指数BC定量识别出作为"踏脚石"的优先保护区域;对于功能不连接的组分,绘制出最小费用路径,确定了该路径中优先恢复区域。结果表明:最佳的最小费用距离阈值为1400,该阈值下猴群主要存在于5个组分中,所有组分中猴群间的连接度优劣排序为组分3组分1组分5组分4,龙马山猴群(G15)没有"踏脚石"斑块使其与同一组分内的其他猴群相连接,应考虑优先恢复该区域的植被,研究成果对于该物种的保护和其他濒危物种的类似研究具有较强的参考价值和借鉴意义。     

新疆塔什库尔干野生动物自然保护区马可波罗盘羊潜在生态廊道识别

识别野生动物的适宜生境并在适宜生境之间构建生态廊道能够提高生境连通性, 有利于加强种群间基因交流并缓解生境破碎化带来的不利影响。本研究基于生境适宜性评价结果确定了塔什库尔干野生动物自然保护区内马可波罗盘羊(Ovis polii)的核心生境斑块, 运用廊道设计模型Linkage Mapper识别最低成本廊道并确定其优先级。结果表明, 马可波罗盘羊适宜生境主要分布在保护区西北部, 核心生境斑块少且破碎化明显, 夏冬两季核心生境斑块均为28个, 潜在生态廊道分别为45和47条。采用成本加权距离与欧几里得距离之比(CWD : EucD)以及成本加权距离与最低成本路径长度之比(CWD : LCP)两种度量方法评估了生态廊道的质量与重要性。以CWD : EucD来衡量, 夏季质量最高的4条廊道分别是皮斯岭至帕日帕克、同库至马尔洋、科克吐鲁克至帕日帕克, 以及哈尔努孜至同库; 冬季质量最高的3条廊道分别是其克尔克尔至亚希洛夫、萨提曼至依西代尔、其克尔克尔至科克吐鲁克。CWD : LCP分析表明, 夏季质量最高的廊道分别是哈尔努孜至阔克加尔和阔克加尔至马尔洋; 冬季质量最高的廊道分别是爱勒米希至塔萨拉、沙尔比列西南至依西代尔。利用流中心性评估各核心生境斑块和廊道的重要性表明, 帕日帕克、塔萨拉和马尔洋这三个斑块在促进马可波罗盘羊迁移扩散方面的贡献值最高。夏季皮斯岭至帕日帕克、同库至马尔洋和马拉特至其克尔克尔这3条廊道的贡献值最高; 冬季爱勒米希至塔萨拉、沙尔比列至沙尔比列西南和铁尔布尔列至沙尔比列这3条廊道的贡献值最高, 上述核心生境斑块和生态廊道在维持保护区马可波罗盘羊种群迁徙扩散中发挥着关键作用。此外, 赞坎、沙尔比列等斑块虽然面积小、贡献值低, 但起到了维持景观中重要斑块连通的踏脚石作用, 其重要性也不可忽略。研究结果可为塔什库尔干野生动物保护区马可波罗盘羊有效保护、保护区功能区划优化以及当地基础建设项目的规划选址提供科学指导。     

Individual dispersal,landscape connectivity and ecological networks

Connectivity is classically considered an emergent property of landscapes encapsulating individuals' flows across space. However, its operational use requires a precise understanding of why and how organisms disperse. Such movements, and hence landscape connectivity, will obviously vary according to both organism properties and landscape features. We review whether landscape connectivity estimates could gain in both precision and generality by incorporating three fundamental outcomes of dispersal theory. Firstly, dispersal is a multi‐causal process; its restriction to an ‘escape reaction’ to environmental unsuitability is an oversimplification, as dispersing individuals can leave excellent quality habitat patches or stay in poor‐quality habitats according to the relative costs and benefits of dispersal and philopatry. Secondly, species, populations and individuals do not always react similarly to those cues that trigger dispersal, which sometimes results in contrasting dispersal strategies. Finally, dispersal is a major component of fitness and is thus under strong selective pressures, which could generate rapid adaptations of dispersal strategies. Such evolutionary responses will entail spatiotemporal variation in landscape connectivity. We thus strongly recommend the use of genetic tools to: (i) assess gene flow intensity and direction among populations in a given landscape; and (ii) accurately estimate landscape features impacting gene flow, and hence landscape connectivity. Such approaches will provide the basic data for planning corridors or stepping stones aiming at (re)connecting local populations of a given species in a given landscape. This strategy is clearly species‐ and landscape‐specific. But we suggest that the ecological network in a given landscape could be designed by stacking up such linkages designed for several species living in different ecosystems. This procedure relies on the use of umbrella species that are representative of other species living in the same ecosystem.