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.     

A Spatially Explicit Model of Functional Connectivity for the Endangered Przewalski’s Gazelle (Procapra przewalskii) in a Patchy Landscape

Background

Habitat fragmentation, associated with human population expansion, impedes dispersal, reduces gene flow and aggravates inbreeding in species on the brink of extinction. Both scientific and conservation communities increasingly realize that maintaining and restoring landscape connectivity is of vital importance in biodiversity conservation. Prior to any conservation initiatives, it is helpful to present conservation practitioners with a spatially explicit model of functional connectivity for the target species or landscape.

Methodology/Principal Findings

Using Przewalski’s gazelle (Procapra przewalskii) as a model of endangered ungulate species in highly fragmented landscape, we present a model providing spatially explicit information to inform the long-term preservation of well-connected metapopulations. We employed a Geographic Information System (GIS) and expert-literature method to create a habitat suitability map, to identify potential habitats and to delineate a functional connectivity network (least-cost movement corridors and paths) for the gazelle. Results indicated that there were limited suitable habitats for the gazelle, mainly found to the north and northwest of the Qinghai Lake where four of five potential habitat patches were identified. Fifteen pairs of least-cost corridors and paths were mapped connecting eleven extant populations and two neighboring potential patches. The least-cost paths ranged from 0.2 km to 26.8 km in length (averaging 12.4 km) and were all longer than corresponding Euclidean distances.

Conclusions/Significance

The model outputs were validated and supported by the latest findings in landscape genetics of the species, and may provide impetus for connectivity conservation programs. Dispersal barriers were examined and appropriate mitigation strategies were suggested. This study provides conservation practitioners with thorough and visualized information to reserve the landscape connectivity for Przewalski’s gazelle. In a general sense, we proposed a heuristic framework for species with similar biological and ecological characteristics.     

基于景观格局和连接度评价的生态网络方法优化与应用

景观生态学中常凭借最小累积阻力模型构建目标种生态网络,以提升破碎栖息地间的景观连接度,缓解生境破碎化负面影响.但传统最小累积阻力生态网络方法缺乏对生态网络的效用验证,对研究地的景观结构变化与生态过程的影响认识不足.本研究运用景观格局指数与连接度概率指数,定量评价生态网络构建前后的研究地景观结构与连接度特征,并以崇左白头叶猴栖息地生态网络为例,详尽叙述此生态网络方法的优化与应用过程.通过对白头叶猴栖息地斑块进行辨认、踏脚石斑块识别,对研究地用地类型进行划分并进行阻力赋值,运用最小累积阻力模型生成了20条白头叶猴栖息地生态网络廊道;然后利用景观结构指数与连接度概率指数结合的方法,对生成的生态网络结构和功能连接度进行评价.结果表明: 凭借最小累积阻力模型构建的目标种生态网络,能有效提升栖息地生境的完整性和连续性,降低总体破碎化水平,并改善生境质量.同时,该生态网络构建能提升生境景观的结构连接度与功能连接度,且两方面的连接度变化在结果上具有极显著的一致性(R²=98.3%,P<0.01).生态网络带来的景观结构方面变化与功能连接度的关联性不强,两种指数间的相互关系不如结构与功能的内在关系显著.     

An exposition of system reliability analysis with an ecological perspective

This paper attempts to set the stage for a prospective interplay between ecology and reliability theory concerning the common issues of network connectivity and redundancy. The paper treats the problem of survival reliability which is the probability of successful migration of a specific species from a critical habitat patch to destination habitat patches via heterogeneous imperfect corridors. The paper surveys techniques of system reliability in an ecological setting and contributes methods for computing a new measure of reliability that arises when paths to destination habitat patches share common corridors. Care is taken to ensure that the reliability expressions obtained are as compact as possible and to check them for correctness.     

Both spatiotemporal connectivity and habitat quality limit the immigration of forest plants into wooded corridors

Extensive afforestation of agricultural areas has increased the importance of green corridors as a dispersal network. We tested the effect of spatiotemporal connectivity, edge effect and habitat structural quality of wooded corridors on the long-term immigration success of forest specialist plants relative to the performance of forest generalists. In agricultural landscapes of central and southern Estonia, we sampled 28 historically connected and 52 isolated tree lines and alleys with a minimum age of 50 years, and 93 edges of ancient forests. The regional pool of common forest plants was compiled using species’ frequency data in 91 ancient forests. Both landscape connectivity and habitat quality affected the richness of response groups, but specialists and generalists responded to different drivers. Forest specialists required long-term neighbourhoods of ancient forest and benefited from a direct connection between forest and corridor. Habitat generalists reacted positively to the recently modified structure of the landscape. When a corridor was connected to forest, the dual edge in the corridor did not result in an increased negative edge effect on forest specialist arrival. Even if both specialists and generalists required wide corridors with optimum shade, forest specialists also benefited from mature overstorey and outward overhanging branches, whereas forest generalists used disturbance-created microhabitats. We conclude that only wooded corridors with long-term connectivity to seed source forests and widely branched tree canopies will function as a green infrastructure supporting forest-specific biodiversity.     

A river-based approach in reconstructing connectivity among protected areas: Insights and challenges from the Balkan region

Global efforts to halt biodiversity loss mandate the establishment of protected areas. In the face of habitat loss and climate uncertainty, large-scale networks of protected areas connected by corridors are needed to increase the dispersal and persistence potential of biota. For example, the recent European Biodiversity Strategy for 2030 defines clear targets for identifying, establishing and integrating ecological corridors, as part of a Trans-European Nature Network. Here, we examined whether rivers could serve as such corridors, facilitating landscape connectivity (i.e. extent to which landscape facilitates or impedes species movement, exchange of genes, natal dispersal and metapopulation dynamics) among protected areas hosted within different countries in the Balkan Peninsula, southeastern Europe. To quantitatively address this question, we calculated the proportion of the river network enclosed within a protected area per country to detect patterns of protection coverage and explored the degree to which spatial connections between 1878 protected areas are supported by the river network. Acknowledging that dams hinder instream continuity, we further quantified potential loss of connections between protected areas caused by the existence of already implemented or planned dam projects upon critical river habitats of endangered fish species. Our results highlight that Balkan rivers have great potential in providing the spatial connections needed to establish landscape connectivity between most of protected areas in the region. Still, heedless hydropower growth and dissimilarities in river protection between neighboring countries remain key challenges for the evolution of a relative framework. Transnational cooperation and systematic planning of infrastructure development could be the only efficient steps towards supporting the establishment of a river-based network to reconstruct connectivity between protected areas and meet biodiversity goals.     

Population genetic structure and connectivity in the endangered Ethiopian mountain Nyala (Tragelaphus buxtoni): recommending dispersal corridors for future conservation

Habitat fragmentation is an increasing threat to wildlife species across the globe and it has been predicted that future biodiversity will decrease rapidly without the intervention of scientifically-based management. In this study we have applied a landscape genetics approach to suggest a network design that will maintain connectivity among populations of the endangered mountain Nyala (Tragelaphus buxtoni) in the fragmented highlands of Ethiopia. DNA was obtained non-invasively from 328 individuals and genetic population structure and gene flow were estimated using 12 microsatellite markers. In addition, a 475-bp segment of the mitochondrial control region was sequenced for 132 individuals. Potential dispersal corridors were determined from least-cost path analysis based on a habitat suitability map. The genetic data indicated limited gene flow between the sampled mountain Nyala populations of the Bale Massif and the Arsi Massif. The genetic differentiation observed among five sampling areas of the Bale Massif followed a pattern of isolation by distance. We detected no impact of habitat resistance on the gene flow. In the future, however, the current expanding human population in the highlands of Ethiopia may reduce the current mountain Nyala habitat and further limit migration. Hence, maintaining habitat connectivity and facilitating survival of stepping-stone populations will be important for the future conservation of the species. The approach used here may also be useful for the study and conservation of other wildlife species inhabiting areas of increasing human encroachment.     

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.     

Assessing the importance of individual habitat patches as irreplaceable connecting elements: An analysis of simulated and real landscape data

Habitat loss and fragmentation are considered to be severe threats to biodiversity, and maintaining natural levels of landscape connectivity may be one of the best responses to these issues. Graph-based habitat availability (reachability) metrics have been shown to be an appropriate method for a multifaceted but coherent landscape connectivity assessment. These metrics can be partitioned into three commensurate fractions (intra, flux, connector) that quantify the different ways in which habitat patches contribute to the overall landscape connectivity and habitat availability. In particular, the connector fraction measures the contribution of patches to the connectivity between other habitat areas as irreplaceable connecting elements or stepping stones. Because many conservation efforts and initiatives are focused on conserving or restoring corridors and other linkages between habitat areas, it is critical to understand more thoroughly the conditions under which investing in these connecting elements is an efficient management strategy. For this purpose, we analysed the contribution of the connector fraction in different simulated habitat patterns under different levels of habitat amount and fragmentation and in natural habitats for endangered forest bird species in Catalonia (Spain). We show that a prominent role of individual stepping stone patches as irreplaceable providers of habitat connectivity and availability arises only under a relatively narrow set of conditions, characterised by low habitat amount, high habitat fragmentation and modest to intermediate species dispersal abilities. We suggest that to support connectivity-related investments, it is necessary to focus on those few species or dispersal distance ranges that are likely to be both most dependent on and most benefited by the conservation or restoration of stepping stone patches. We conclude that the total amount of reachable habitat for a particular species is rarely determined by the contribution of individual connectors as the only dominant factor. Therefore, conservationists should be cautious not to overemphasise the importance of connectivity investments and to balance them with other conservation alternatives and strategies to promote species conservation in heterogeneous landscapes.     

Comparing Linkage Designs Based on Land Facets to Linkage Designs Based on Focal Species

Least-cost modeling for focal species is the most widely used method for designing conservation corridors and linkages. However, these designs depend on today''s land covers, which will be altered by climate change. We recently proposed an alternative approach based on land facets (recurring landscape units of relatively uniform topography and soils). The rationale is that corridors with high continuity of individual land facets will facilitate movement of species associated with each facet today and in the future. Conservation practitioners might like to know whether a linkage design based on land facets is likely to provide continuity of modeled breeding habitat for species needing connectivity today, and whether a linkage for focal species provides continuity and interspersion of land facets. To address these questions, we compared linkages designed for focal species and land facets in three landscapes in Arizona, USA. We used two variables to measure linkage utility, namely distances between patches of modeled breeding habitat for 5–16 focal species in each linkage, and resistance profiles for focal species and land facets between patches connected by the linkage. Compared to focal species designs, linkage designs based on land facets provided as much or more modeled habitat connectivity for 25 of 28 species-landscape combinations, failing only for the three species with the most narrowly distributed habitat. Compared to land facets designs, focal species linkages provided lower connectivity for about half the land facets in two landscapes. In areas where a focal species approach to linkage design is not possible, our results suggest that conservation practitioners may be able to implement a land facets approach with some confidence that the linkage design would serve most potential focal species. In areas where focal species designs are possible, we recommend using the land facet approach to complement, rather than replace, focal species approaches.     

Identifying potential conservation areas in the Cuitzeo Lake basin,Mexico by multitemporal analysis of landscape connectivity

Lake Cuitzeo basin is an important ecological area subjected to strong human pressure on forest covers that are key elements for the long-term support of biodiversity. We studied landscape connectivity changes for the years 1975, 1996, 2000, 2003 and 2008 to identify potential conservation areas in the basin. We modeled potential distributions of the Mexican bobcat (Lynx rufus escuinapae) and the ringtail (Bassariscus astutus) – two terrestrial mammal focal species with contrasting dispersal capacities – and we determined their habitat availability and suitability in the basin. We then identified their optimal habitat patches and produced landscape cumulative resistance maps, estimated least-cost paths (graph theory approach), and elaborated current flow maps (circuit theory approach). For evaluation of landscape connectivity, we applied an integral index of connectivity (IIC) to each study period, and determined individual habitat patch contribution to the overall landscape connectivity. The IIC index had very low values associated with reduced availability of focal species habitat. However, our study showed the conservation importance of the surface of optimal habitat patch areas. The combined application of a graph-based approach and current flow mapping were useful, and complementary both in terms of estimating potential dispersal corridors and identifying high probability dispersal areas. This indicated that landscape connectivity analysis is a useful tool for identification of potential conservation areas and for local landscape planning.     

不同鸟类生境网络复合与优化——以苏锡常地区白鹭、鸳鸯、雉鸡为例

通过复合优化不同焦点物种的生境网络表征多数物种生境网络实现物种多样性保护,具有重要理论价值和实践意义。以苏锡常地区为研究区域,以白鹭、鸳鸯和雉鸡3种鸟类为焦点物种,通过采用生境斑块约束条件模型与最小成本路径法相结合的方法识别出生境网络;从满足集合覆盖问题视角出发,通过采用网络构成要素复合的方法进行网络复合,其中廊道与廊道的复合通过采用评价生态系统服务价值的方法实现;通过采用观测数据为生境斑块和迁移廊道增补依据的方法进行复合生境网络优化。结果表明:生境网络经过复合,廊道总面积、总长度及生态系统服务价值在分别减少了16%、68%和10%的情况下,保持了斑块间的连接度、兼顾到经济效益和生态效益最大化、覆盖了占总数86%以上的75处观测点;复合生境网络经过优化,覆盖了2010年及以后所有84处观测点,廊道总面积、总长度及生态系统服务价值分别增加了19%、21%和27%;说明生境网络复合优化定量分析方法和思路具有可行性,为网络复合研究提供了借鉴。     

生态网络视角下武汉市湿地生态格局分析

城市湿地是城市发展的重要生态保障。快速城市化进程导致湿地景观破碎化,威胁湿地生态系统安全。生态网络通过廊道连接重要生境斑块,基于生态网络分析城市湿地生态格局,不仅可了解湿地的空间分布情况,还可反映湿地系统的结构与连通性特征。以武汉市为研究区,利用形态学空间格局分析(Morphological Spatial Pattern Analysis, MSPA)方法识别湿地源地,结合地表景观类型、地形坡度及人类活动强度因素构建综合阻力面,采用最小累积阻力模型(Minimum Cumulative Resistance, MCR)提取生态廊道构建湿地生态网络,最后对网络进行重要性分级。分析网络的结构及区域特征,结果表明:武汉市湿地规模较大,但破碎化严重且空间分布不均;网络空间结构不完备但景观结构良好,重要廊道多位于城市边缘斑块间且集中分布在南部地区;各区域湿地格局特征不同,江夏区及汉南区湿地资源丰富且斑块质量高,廊道分布多且景观结构较好但重要性不高,黄陂区及东西湖区湿地总量少且形态破碎,区内廊道少、重要性低且景观结构有待改善,新洲区湿地规模小,廊道分布较少且景观结构不完善,但湿地及廊道重要性均较高。研究结果将为武汉市湿地保护与建设工作提供科学依据。     

基于电路理论的南京城市绿色基础设施格局优化

城市绿色基础设施的连通性与格局优化能显著提升城市的生物多样性和可持续发展能力,对维持城市生态系统的健康与稳定具有重要意义。基于电路理论构建了南京市主城区绿色基础设施景观格局,根据电流密度分析斑块、廊道重要性,并借助移动窗口搜索法识别障碍点,提出南京市景观格局优化策略。研究结果表明:(1)南京主城区景观破碎化程度较高,40%的生境斑块(约为28.18 km2)对连通性的贡献较低,南部重要廊道的数量最多,局部簇团成网,网络结构较为复杂,其次为中部,且河流廊道(秦淮河)是其主要廊道类型,北部廊道数量最少,斑块多呈孤岛分布;(2)研究区共有155处障碍点,其中84.5%面积小于5hm2,可见主城区景观连通性仍有较大的提升空间。研究丰富了城市绿色基础设施景观格局的构建方法,对南京主城区绿色基础设施的连通性与格局优化具有一定的实践指导意义与参考价值。     

Effects of slope and riparian habitat connectivity on gene flow in an endangered Panamanian frog, Atelopus varius

Aim Understanding how heterogeneous landscapes shape genetic structure not only sheds light on processes involved in population divergence and speciation, but can also guide management strategies to promote and maintain genetic connectivity of populations of endangered species. This study aimed to (1) identify barriers and corridors for gene flow among populations of the endangered frog, Atelopus varius and (2) assess the relative contributions of alternative landscape factors to patterns of genetic variation among these populations in a hypothesis testing framework. Location This study took place in western Panama and included all nine of the remaining known populations of A. varius at the time of study. Methods The influence of landscape variables on gene flow among populations was examined by testing for correlations between alternative landscape‐resistance scenarios and genetic distance. Fifteen alternative hypotheses about the influence of (1) riparian habitat corridors, (2) steep slopes, and (3) climatic suitability on patterns of genetic structure were tested in a causal modelling framework, using Mantel and partial‐Mantel tests, along with an analysis of molecular variation. Results Only the hypothesis attributing resistance to dispersal across steep slopes (genetic isolation by slope distance) was fully supported by the causal modelling approach. However, the analysis of molecular variance and the paths of least‐slope among populations suggest that riparian habitat connectivity may influence genetic structure as well. Main conclusions These results suggest that patterns of genetic variation among A. varius populations are affected by the slope of the landscape such that areas with steep slopes act as barriers to gene flow. In contrast, areas of low slope, such as streams and mountain ridges, appear to be important corridors for gene flow, especially among high elevation populations. These results engender important considerations for the management of this critically endangered species.     

Modeling ecological minimum requirements for distribution of greater sage‐grouse leks: implications for population connectivity across their western range,U.S.A

Greater sage‐grouse Centrocercus urophasianus (Bonaparte) currently occupy approximately half of their historical distribution across western North America. Sage‐grouse are a candidate for endangered species listing due to habitat and population fragmentation coupled with inadequate regulation to control development in critical areas. Conservation planning would benefit from accurate maps delineating required habitats and movement corridors. However, developing a species distribution model that incorporates the diversity of habitats used by sage‐grouse across their widespread distribution has statistical and logistical challenges. We first identified the ecological minimums limiting sage‐grouse, mapped similarity to the multivariate set of minimums, and delineated connectivity across a 920,000 km² region. We partitioned a Mahalanobis D² model of habitat use into k separate additive components each representing independent combinations of species–habitat relationships to identify the ecological minimums required by sage‐grouse. We constructed the model from abiotic, land cover, and anthropogenic variables measured at leks (breeding) and surrounding areas within 5 km. We evaluated model partitions using a random subset of leks and historic locations and selected D² (k = 10) for mapping a habitat similarity index (HSI). Finally, we delineated connectivity by converting the mapped HSI to a resistance surface. Sage‐grouse required sagebrush‐dominated landscapes containing minimal levels of human land use. Sage‐grouse used relatively arid regions characterized by shallow slopes, even terrain, and low amounts of forest, grassland, and agriculture in the surrounding landscape. Most populations were interconnected although several outlying populations were isolated because of distance or lack of habitat corridors for exchange. Land management agencies currently are revising land‐use plans and designating critical habitat to conserve sage‐grouse and avoid endangered species listing. Our results identifying attributes important for delineating habitats or modeling connectivity will facilitate conservation and management of landscapes important for supporting current and future sage‐grouse populations.     

Corridors and barriers in biodiversity conservation: a novel resource-based habitat perspective for butterflies

Habitat loss and fragmentation, exacerbated by projected climate change, present the greatest threats to preservation of global biodiversity. As increasing habitat fragmentation and isolation of residual fragments exceeds the dispersal capacity of species, there is the growing need to address connectivity to maintain diversity. Traditionally, habitat corridors have been proposed as a solution. But, the concept of corridors (barriers) is poorly understood; typically they are defined as linear habitats linking up habitat patchwork, and are advocated without a detailed understanding of the elements making up species’ habitats and the cost-effectiveness of alternative solutions. Yet, landscapes comprise an enormous range of ‘linear’ structures that can function in different ways to promote species’ persistence and diversity. In this review, a functional definition of corridor (barrier) is developed to give prominence to connectivity as opposed to ad hoc structures purported to advance connectivity. In developing the concept, urgency to accommodate environmental changes compels a growing emphasis on organism diversity rather than a preoccupation with single species conservation. The review, in focusing on butterflies to address the issue of corridors for patchwork connectivity, draws attention to fundamental divisions among organisms in any taxon: generalists and specialists. Both groups benefit from large patches as these necessarily house species with specialist resources as well as generalists with very different resource types. But, generalists and specialists require very different solutions for connectivity, from short-range habitat corridors and gateways for specialists to habitat and resource stepping stones (nodes, surfaces) for generalists. Connectivity over extensive areas is most critical for moderate generalists and their conservation requires emphasis being placed on space–time resource heterogeneity; landscape features, of whatever dimensionality and structure, provide a vital framework for developing the variety of suitable conditions and resources for enhancing their diversity.     

基于生境组团化分析与景观廊道模拟的南京市白鹭生境网络构建与优化

保持生境连通性是全球生物多样性保护面临的主要挑战之一。生境网络构建与优化是一种积极主动的景观策略,但其成效取决于异质性景观背景下生境分布格局与物种响应。以南京市为例、白鹭为目标物种,开展了基于生境组团化分析与景观廊道(LSCorridors)模拟的生境网络构建与优化研究。通过整合生境适宜性评价、干扰度评价、最大熵(MaxEnt)模型模拟,实现了物种生境源地综合识别;利用景观连通性指标与核密度分析,识别了物种生境分布的组团化格局;在最小成本路径(LCPs)的基础上,定义了优化新增型与提升型两类廊道,并从物种感知与适应性变化出发,应用LSCorridors软件模拟了这两类目标优化廊道的多重随机路径及其空间范围。结果表明,南京市白鹭生境斑块共计428个,总面积达31525.75 hm²,主要是林地与水域,具有较为明显的破碎化和局部集聚特征,九大生境组团以南京长江段水域斑块为轴,沿两侧分布,彼此联系比较薄弱;最佳距离阈值4.5 km内,识别LCPs共907条,总长度1548.59 km,平均较短、分布紧凑,主要位于各生境组团内部,但仅少数连接着不同生境组团;确定的8条优化新增型廊道和10条优化提升型廊道,其LSCorridors模拟结果与LCPs存在空间偏差,前者更符合现实进而有益于避免保护低效和促进多类型、差异化的优化措施制定。研究成果能为面向生物多样性保护的南京市生境网络保护以及重点生态廊道的规划实践提供决策参考。     

Understanding the Relationships between Landscape Connectivity and Abundance of Ixodes ricinus Ticks

The density of Ixodes ricinus ticks in a heterogeneous landscape of northern Spain was determined and associated with some aspects of habitat topology. The habitat mosaic was used to quantify connectivity between patches of different tick density. The analysis revealed that patches with high tick abundance are ‘stepping-stone’ territories that, when removed from the landscape, cause large changes in connectivity. Sites with medium tick abundance do not cause such a critical transition in connectivity. Patches with low tick abundance, but optimal abiotic conditions for survival are located within the minimum cost corridors network joining the patches, while those sites where the tick has been intermittently collected are located at variable distances from this network. These results suggest that tick distribution in a zone is highly affected not only by abiotic variables (vegetation and weather) but also by host movements. Whether these high-density ‘stepping-stone’ patches occur in other tick species needs to be evaluated because of the potential implications of these foci for human health. This revised version was published online in July 2006 with corrections to the Cover Date.