Article

Improving landscape connectivity for the Yunnan snub-nosed monkey through cropland reforestation using graph theory

Authors:
  • Chongqing Academy of Social Sciences
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Abstract

Habitat fragmentation is a threat to biodiversity because it restricts the ability of animals to move. Maintaining landscape connectivity could promote connections between habitat patches, which is extremely important for the preservation of gene flow and population viability. This paper aims to evaluate the landscape connectivity of forest areas as it relates to the conservation of the Yunnan snub-nosed monkey (Rhinopithecus bieti), an emblematic and endemic endangered primate species. Specifically, this study seeks to model ways to improve connectivity via cropland reforestation scenarios which incorporate graph theory and genetic distances. The connectivity improvement assessment is performed at two nested scales. At the regional scale, the aim is to quantitatively assess the gain in connectivity from different reforestation scenarios, in which croplands are replaced by different kinds of forest habitats. At the local scale, the goal is to prioritize and to locate croplands based on the gain in connectivity that they would provide if they were reforested. The results indicate that the four reforestation scenarios have different impacts on connectivity; the fourth scenario, in which reforestation is accomplished with plant species that provide optimal monkey habitat, yields the greatest increase in connectivity (+24% versus less than +2% for the others). Prioritization of the 1482 cropland patches shows that the 10 best patches increase connectivity from 0.04% to 9.1% as the isolation threshold distance increases. This kind of graph theoretic approach appears to be a useful tool for connectivity assessment and the development of conservation measures for species impacted by human activities.

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... Therefore, we need to carry out ecological restoration projects in these areas through cropland reforestation. We need to promote the restoration of the Huashan pine hemlock arrow bamboo forests, spruce fir forests, and mixed coniferous and broad-leaved forests to improve habitat quality [4]. Bamboo and lichen are important food sources for Yunnan snub-nosed monkeys [10]. ...
... We should enhance habitat connectivity and build up ecological corridors to promote gene exchange and conserve genetic diversity in these areas where connectivity with other monkey groups is impeded by agriculture and grazing land, roads, and villages. This is especially true for the isolated monkey groups (C3, C6, and C14) [4][5][6]44]. ...
... The study area and locations of monkey groups in Yunnan Province (China). The numbers labeling each green area represent the monkey group number(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15). ...
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... Concerning ecological compensation or mitigation, Graphab has been applied in response to the question: Where are the most relevant locations to design or plan actions promoting access to ecological habitats? Studies have been made to establish compensation sites following the implantation of a highway [44] or a sports infrastructure [45], for restoring ecological habitats [46][47][48][49], for developing wildlife crossings over a highway [50,51], or even for evaluating the pooling of biodiversity offsets [52]. Graphab has also been used to choose optimal field locations for implementing agroecological measures to reduce habitat connectivity of a rodent whose swarming causes substantial ecological and economic damage [53,54]. ...
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Land use has generally been considered a local environmental issue, but it is becoming a force of global importance. Worldwide changes to forests, farmlands, waterways, and air are being driven by the need to provide food, fiber, water, and shelter to more than six billion people. Global croplands, pastures, plantations, and urban areas have expanded in recent decades, accompanied by large increases in energy, water, and fertilizer consumption, along with considerable losses of biodiversity. Such changes in land use have enabled humans to appropriate an increasing share of the planet's resources, but they also potentially undermine the capacity of ecosystems to sustain food production, maintain freshwater and forest resources, regulate climate and air quality, and ameliorate infectious diseases. We face the challenge of managing trade-offs between immediate human needs and maintaining the capacity of the biosphere to provide goods and services in the long term.
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Predicting population-level effects of landscape change depends on identifying factors that influence population connectivity in complex landscapes. However, most putative movement corridors and barriers have not been based on empirical data. In this study, we identify factors that influence connectivity by comparing patterns of genetic similarity among 146 black bears (Ursus americanus), sampled across a 3,000-km(2) study area in northern Idaho, with 110 landscape-resistance hypotheses. Genetic similarities were based on the pairwise percentage dissimilarity among all individuals based on nine microsatellite loci (average expected heterozygosity=0.79). Landscape-resistance hypotheses describe a range of potential relationships between movement cost and land cover, slope, elevation, roads, Euclidean distance, and a putative movement barrier. These hypotheses were divided into seven organizational models in which the influences of barriers, distance, and landscape features were statistically separated using partial Mantel tests. Only one of the competing organizational models was fully supported: patterns of genetic structure are primarily related to landscape gradients of land cover and elevation. The alternative landscape models, isolation by barriers and isolation by distance, are not supported. In this black bear population, gene flow is facilitated by contiguous forest cover at middle elevations.
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Abstract A huge road network with vehicles ramifies across the land, representing a surprising frontier of ecology. Species-rich roadsides are conduits for few species. Roadkills are a premier mortality source, yet except for local spots, rates rarely limit population size. Road avoidance, especially due to traffic noise, has a greater ecological impact. The still-more-important barrier effect subdivides populations, with demographic and probably genetic consequences. Road networks crossing landscapes cause local hydrologic and erosion effects, whereas stream networks and distant valleys receive major peak-flow and sediment impacts. Chemical effects mainly occur near roads. Road networks interrupt horizontal ecological flows, alter landscape spatial pattern, and therefore inhibit important interior species. Thus, road density and network structure are informative landscape ecology assays. Australia has huge road-reserve networks of native vegetation, whereas the Dutch have tunnels and overpasses perforating road barriers to enhance ecological flows. Based on road-effect zones, an estimated 15–20% of the United States is ecologically impacted by roads.
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Ecologists are familiar with two data structures commonly used to represent landscapes. Vector-based maps delineate land cover types as polygons, while raster lattices represent the landscape as a grid. Here we adopt a third lattice data structure, the graph. A graph represents a landscape as a set of nodes (e.g., habitat patches) connected to some degree by edges that join pairs of nodes functionally (e.g., via dispersal). Graph theory is well developed in other fields, including geography (transportation networks, routing applications, siting problems) and computer science (circuitry and network optimization). We present an overview of basic elements of graph theory as it might be applied to issues of connectivity in heterogeneous landscapes, focusing especially on applications of metapopulation theory in conservation biology. We develop a general set of analyses using a hypothetical landscape mosaic of habitat patches in a nonhabitat matrix. Our results suggest that a simple graph construct, the minimum spanning tree, can serve as a powerful guide to decisions about the relative importance of individual patches to overall landscape connectivity. We then apply this approach to an actual conservation scenario involving the threatened Mexican Spotted Owl (Strix occidentalis lucida). Simulations with an incidence-function metapopulation model suggest that population persistence can be maintained despite substantial losses of habitat area, so long as the minimum spanning tree is protected. We believe that graph theory has considerable promise for applications concerned with connectivity and ecological flows in general. Because the theory is already well developed in other disciplines, it might be brought to bear immediately on pressing ecological applications in conservation biology and landscape ecology.
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Fingerprint image enhancement is a essential preprocessing step to ensure good performance in Automatic Fingerprint Identification System (AFIS). In this paper, we proposed a new fingerprint enhancement algorithm based on morphological filter. This algorithm first employs the idea of median filtering based on the Mehtre method to obtain a reliable ridge orientation field. And then it designes a morphological structuring element database to save structuring element templates of all directions. Finally, in order to remove the empty and rupture in the ridge, the morphological closing operation is employed through selecting the corresponding template according to the local ridge orientation. We have tested the algorithm on FVC2004 fingerprint database DB2. Experimental results indicate that the proposed algorithm can obtain great results at both the orientation field estimation and the minutiae detection performance.
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Recent years have shown a rapid increase in the number of published studies that advocate network analysis (graph theory) to ecologically manage landscapes that suffer from fragmentation and loss of connectivity. This paper studies the reasons, benefits and difficulties of using network analysis to manage landscape fragmentation in the practice of land-use planning. The results are based on interviews with thirteen municipal ecologists and environmental planners in Stockholm, Sweden, who had been introduced to a GIS-tool for network-based connectivity analysis. Our results indicate that fragmentation is not considered enough in municipal planning and demonstrate that none of the interviewed practitioners used systematic methods to assess landscape connectivity. The practitioners anticipate that network-level and patch-level connectivity measures and maps would help them to communicate the meaning and implications of connectivity to other actors in the planning process, and to better assess the importance of certain habitats affected by detailed plans. The main difficulties of implementing network-based connectivity analyses reported by the respondents related to the choice of focal species and the lack of model input in terms of landscape data and dispersal distances. The main strengths were expressed by the practitioners as graphical, quantitative and credible results; the ability to compare planning alternatives and to find critical sites in a more objective manner than today; and to relate local planning and ecology to the regional structure of the landscape. Many respondents stressed the role of fragmentation assessments in the endeavor to overcome current spatial mismatches of ecological and administrative scales.
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Fragmentation of habitats is a serious problem for many endangered species; a possible solution is the maintenance of landscape connectivity. Due to scarce sources, in managing and planning landscapes exact and quantitative priorities must be set. Application of mathematical tools, such as network analysis, can be useful help in these decisions. We illustrate the possibilities and results of this approach with a case study of endangered Pholidoptera transsylvanica bush-cricket population in the Aggtelek Karst, Northeast-Hungary, which inhabits 39 habitat patches connected with ecological corridors. A key issue in the long-term survival of this metapopulation is the maintenance of gene flow (by preserving the connectivity of the habitat network). We evaluated the landscape graph and our results are compared to earlier ones based on older methods. During the comparison, we used several network indices to set quantitative conservation preferences. In addition, we would like to draw attention to the need for constant monitoring (and possible treatments), because several changes (like secondary succession) have occurred during the years between the two studies, threatening landscape connectivity and long-term survival of certain species. A potential solution for preventing fragmentation is establishing new corridors or improving the existing ones: we estimated the possible effects of these changes. New corridors did not have major effect on the system; maintaining already functioning corridors is more effective.
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Connectivity is an important but inconsistently defined concept in spatial ecology and conservation biology. Theoreticians from various subdisciplines of ecology argue over its definition and measurement, but no consensus has yet emerged. Despite this disagreement, measuring connectivity is an integral part of many resource management plans. A more practical approach to understanding the many connectivity metrics is needed. Instead of focusing on theoretical issues surrounding the concept of connectivity, we describe a data-dependent framework for classifying these metrics. This framework illustrates the data requirements, spatial scales, and information yields of a range of different connectivity measures. By highlighting the costs and benefits associated with using alternative metrics, this framework allows practitioners to make more informed decisions concerning connectivity measurement.
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Since landscape connectivity reflects a basic form of interaction between species and their environment, the modelling of landscape networks is currently an important issue for researchers in ecology and practitioners of landscape management alike. Graph-based modelling has recently been shown to be a powerful way of representing and analysing landscape networks. Graphab 1.0 is designed as a package integrating a complete set of connectivity analysis functions. The application can build graphs from a given landscape map by exploring several possibilities for link topology, types of distances and graph definitions. A wide range of connectivity metrics can be computed from these graphs at the global, component or local levels. By extrapolating patch-based metrics outside of the graph using a distance-dependent function, the relationship between the graph and any set of point data can be established in order to compare the connectivity properties of the landscape network and field observations of a given species. In conclusion, Graphab 1.0 provides a full set of coherent modelling functions for analysing and exploring landscape graphs with a single application.
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Connectivity is a key concern in natural resource planning. Many studies have focused on the development of methods, tools and indices for the assessment of both components of connectivity: structural and functional. In particular, approaches based on graph theory principles have been recently proposed and are being increasingly applied to guide landscape connectivity conservation. However, forest planners and managers still need effective and operational methodologies to detect those landscapes where connectivity should be treated as a particularly critical conservation concern. In addition, in the Mediterranean, as in other parts of the world, socioeconomic changes in the last decades have driven the abandonment of many formerly cultivated lands. This poses both a challenge and an opportunity for managers intending to restore ecological connectivity in forested areas. In this context, setting adequate priorities for the reforestation of agricultural lands is of outmost importance. Here we show how a two-stage hierarchical methodology based on network analysis can be used to meet these needs. In particular, we apply a graph metric based on the measurement of habitat availability at the landscape scale (the Integral Index of Connectivity) to two Mediterranean forest districts in Spain with different management objectives and environmental heterogeneity. First, we identify those landscapes where efforts to improve forest connectivity should be concentrated. In a second stage, we prioritize within those landscapes the individual patches of agricultural lands that, being available for a potential reforestation program, would contribute most to uphold connectivity and ecological flows at wide spatial scales. We show how the extent of the agricultural patches is not strictly related to the contribution to connectivity they would provide if reforested, and how the results of such analysis vary with species traits (dispersal capabilities). We discuss the suitability of the proposed approach for forest landscape planning purposes and conclude that it can provide a useful diagnosis and helpful guidelines for the development of efficient reforestation programs that might be applied in a variety of situations for improving the ecological coherence of forest landscapes.
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Creation of new habitat could help species respond to climate change by facilitating range expansion in fragmented landscapes. However, there are currently no guidelines for deciding where new habitat should be placed to promote range changes. We developed a model to simulate the expansion of populations across a heavily fragmented landscape in the United Kingdom, and investigated the effectiveness of six habitat creation strategies for woodland, grassland, heathland, and wetland habitats. A strategy aimed at linking clusters of habitat patches was most effective for three of the four habitat types. Adding habitat evenly or randomly across the landscape, or according to stakeholder suggestions, were consistently better strategies than increasing aggregation of habitat. The results highlight that the best spatial pattern to facilitate range expansion is different from the best pattern to prevent extinction.
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Variation at both the patch and landscape scale is known to influence the distribution and abundance of arboreal monkeys in rainforest fragments. However, few studies have examined the factors associated with these different scales of focus simultaneously. Using stepwise logistic-regression and generalized linear models (GLMs), howler monkey Alouatta palliata distribution and abundance were examined as a function of patch quality (fragment area, shape, tree DBH and canopy height) and landscape connectivity (isolation, total forest area, fragment and road abundance, corridor abundance and length) in 119 rainforest fragments in northern Chiapas, Mexico. The positive correlation observed between monkey distribution (presence/absence) and both fragment area and abundance may be explained by increased resources within larger fragments and those whose proximity allows greater exploration by monkeys. In contrast, GLM analysis indicated that monkey abundance in inhabited fragments was positively correlated with corridor abundance, canopy height and fragment area. These relationships could be explained by greater reproductive investments by monkeys in forest fragments whose size, degree of perturbation and degree of connectivity with other fragments suggest greater overall resource availability. Future studies should explicitly include a multi-scale approach to understanding the factors affecting patterns of monkey distribution and abundance, particularly as this relates to measures of and interactions between patch connectivity and resource availability.
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a b s t r a c t Development pressure on biodiversity reserve networks in densely populated countries may lead to the decision to compensate for biotope loss by improving connectivity. Such a decision makes sense, if cre-ation of new biotopes takes too long and if improving population exchange is a conservation target of the reserve network. To explore the impact of such decisions, we analyse four compensation scenarios. The scenarios vary in how strong loss and compensation is locally fixed. The reserve network was modelled as a graph where biotope patches are represented by nodes and connectivity corresponds to edges along which animals migrate from patch to patch. Connectivity improvement was modelled as a reduction of edge lengths. Ecological equivalence is measured by metapopulation capacity as defined by Hanski and Ovaskainen (2000). Localised modifications were analysed with eigenanalysis. Modifications spread over the whole component were analyzed with a linear regression model which uses the total biotope area and the length of the minimal spanning tree as input. Our results show that both general connectiv-ity improvement and clearly localised connectivity improvement can be efficient compensation measures for area loss. Local measures best focus on connectivity improvement between the largest patches. For Switzerland's dry grassland reserve network, we found that in general, for half of the patches it is possible to compensate an area loss of 100 m 2 by a connectivity improvement equivalent to an edge length reduc-tion of less then 3 m. Our results show that connectivity improvement is a valuable compensation alter-native to creation of new patches.
Article
Graph structures and habitat availability metrics are two recent and complementary approaches for analysing landscape connectivity. They have gained rapid popularity and provided significant conceptual improvements for decision making in conservation planning. We present a further methodological development of the habitat availability concept and metrics by partitioning them into three separate fractions that quantify the different ways in which individual landscape elements can contribute to overall habitat connectivity and availability in the landscape, including stepping stone effects. These fractions are derived from the same concept, are measured in the same units and can be directly compared and combined within a unifying framework. This avoids the problematic and, so far, usual combination of metrics coming from different backgrounds and the arbitrary weighting of connectivity considerations in a broader context of conservation alternatives. We analyse how the relative importance of each fraction varies with species traits. In addition, we show how the critical patches differ for each of the fractions by analysing various forest habitats in the province of Lleida (NE Spain). We discuss the conceptual and conservation implications of this approach, which can be adapted to different degrees of ecological and spatial detail within the graph while still maintaining a coherent framework for the identification of critical elements in the landscape network.
Article
Yunnan, an inland province at a low latitude and high elevation, lying between 2109–2915 N and 9732–10612 E in southwestern China, has a vast territory with diversified and unique nature resources. There are more than 18000 high plant species (51.6% of China's total) and 1836 vertebrate species (54.8% of China's total) living in Yunnan on a land area of 39.4 104km2, i.e., only 4.1% of China's total. Among 15000 seed plants found in Yunnan there are 151 rare and endangered plant species (42.6% of China's protected plants). Out of 335 China priority protected wild animals, Yunnan has 243 species, accounting for 72.5% of China's total, 15% of which are species endemic to Yunnan. However, Yunnan's biodiversity is faced with the menace of excessive exploitation of resources and changes in environmental conditions caused by the activities of an expanding human population. This paper discusses the background, the composition, and the structure of Yunnan's biodiversity. Its biodiversity fragility and the threatened situation are also discussed. Suggestions and recommendations on the strategy and actions of Yunnan biodiversity conservation and sustainable development are proposed.
Article
Since the fragmentation of natural habitats is one of the most serious problems for many endangered species, it is highly interesting to study the properties of fragmented landscapes. As a basic property, landscape connectivity and its effects on various ecological processes are frequently in focus. First, we discuss the relevance of some graph properties in quantifying connectivity. Then, we propose a method how to quantify the relative importance of habitat patches and corridors in maintaining landscape connectivity. Our combined index explicitly considers pure topological properties and topographical measures, like the quality of both patches (local population size) and corridors (permeability). Finally, for illustration, we analyze the landscape graph of the endangered, brachypterous bush-cricket Pholidoptera transsylvanica. The landscape contains 11 patches and 13 corridors and is situated on the Aggtelek Karst, NE-Hungary. We characterize the importance of each node and link of the graph by local and global network indices. We show how different measures of connectivity may suggest different conservation preferences. We conclude, accordingly to our present index, by identifying one specific habitat patch and one specific corridor being in the most critical positions in maintaining connectivity.
Article
Metapopulation theory teaches that the viability of metapopulations may be enlarged by decreasing the probability of extinction of local populations, or by increasing the colonization probability of empty habitat patches. In a metapopulation model study it has recently been found that reducing the extinction probability of the least extinction-prone patch and increasing the colonization probability between the two least extinction-prone patches are the best options to prolong the expected lifetime of a metapopulation. In this article I examine with a more detailed model whether this translates into enlarging the largest patch and reducing the interpatch distance between the largest patches. Using two measures of metapopulation persistence (longevity and resilience) I found, firstly, that the largest patch should generally be enlarged if the choice is to enlarge a patch by a certain percentage (relative change) and that the smallest patch should generally be enlarged if the choice is to enlarge a patch by a fixed amount of area (absolute change), and secondly that indeed one should reduce the interpatch distance between the two largest patches, if the choice is among all pairs of patches. The strength of these rules of thumb (particularly the second part of the first rule) depends on the parameter values, particularly the amount of clustering of patches, the mean dispersal distance and the number of dispersers. Also, the rules of thumb are less pronounced when resilience is chosen as a measure of metapopulation persistence than when longevity is chosen.
Article
Graph theoretic approaches have received increased interest recently in landscape planning and conservation in the terrestrial realm, because these approaches facilitate the effective modelling of connectivity among habitats. We examined whether basic principles of graph theory can be extended to other ecosystems. Specifically, we demonstrate how a network-based context can be used for enhancing the more effective conservation of riverine systems. We first show how to use graph theoretic techniques to model riverscapes at the segment level. Then we use a real stream network (Zagyva river basin, Hungary) to examine the topological importance of segments in maintaining riverscape connectivity, using betweenness centrality, a commonly used network measure. Using the undirected graph model of this riverscape, we then prioritize segments for conservation purpose. We examine the value of each of the 93 segments present in the Zagyva river basin by considering the conservation value of local fish assemblages, connectivity and the size of the habitat patches. For this purpose we use the ‘integral index of connectivity’, a recently advocated habitat availability index. Based on the results the selection of the most valuable habitat segments can be optimized depending on conservation resources. Because of their inherent advantage in the consideration of connectivity relationships, we suggest that network analyses offer a simple, yet effective tool for searching for key segments (or junctions) in riverscapes for conservation and environmental management. Further, although the joint consideration of aquatic and terrestrial networks is challenging, the extension of network analyses to freshwater systems may facilitate the more effective selection of priority areas for conservation in continental areas.
Article
Here we propose an integrated framework for modeling connectivity that can help ecologists, conservation planners and managers to identify patches that, more than others, contribute to uphold species dispersal and other ecological flows in a landscape context. We elaborate, extend and partly integrate recent network-based approaches for modeling and supporting the management of fragmented landscapes. In doing so, experimental patch removal techniques and network analytical approaches are merged into one integrated modeling framework for assessing the role of individual patches as connectivity providers. In particular, we focus the analyses on the habitat availability metrics PC and IIC and on the network metric Betweenness Centrality. The combination and extension of these metrics jointly assess both the immediate connectivity impacts of the loss of a particular patch and the resulting increased vulnerability of the network to subsequent disruptions. In using the framework to analyze the connectivity of two real landscapes in Madagascar and Catalonia (NE Spain), we suggest a procedure that can be used to rank individual habitat patches and show that the combined metrics reveal relevant and non-redundant information valuable to assert and quantify distinctive connectivity aspects of any given patch in the landscape. Hence, we argue that the proposed framework could facilitate more ecologically informed decision-making in managing fragmented landscapes. Finally, we discuss and highlight some of the advantages, limitations and key differences between the considered metrics.
Article
Graph theory and network analysis have become established as promising ways to efficiently explore and analyze landscape or habitat connectivity. However, little attention has been paid to making these graph-theoretic approaches operational within landscape ecological assessments, planning, and design. In this paper, a set of both theoretical and practical methodological developments are presented to address this issue. In highly fragmented landscapes, many species are restricted to moving among small, scattered patches of different resources, instead of one, large patch. A life-cycle based approach is therefore introduced, in which a metapatch is constructed, spanning over these resources, scattered across the landscape. The importance of spatially explicit and geographically defined representations of the network in urban and regional planning and design is stressed, and appropriate, context-dependent visualizations of these are suggested based on experience from real-world planning cases. The study moves beyond the issue of conservation of currently important structures, and seeks to identify suitable redesigns of the landscape to improve its social–ecological qualities, or increase resilience. By introducing both a system-centric and a site-centric analysis, two conflicting perspectives can be addressed. The first answers the question “what can I do for the network”, and the second, “what can the network do for me”. A method for typical planning strategies within each of these perspectives is presented. To illustrate the basic principles of the proposed methods, an ecological study on the European common toad (Bufo bufo) in Stockholm, Sweden is presented, using the betweenness centrality index to capture important stepping-stone structures.
Article
We use focal-species analysis to apply a graph-theoretic approach to landscape connectivity in the Coastal Plain of North Carolina. In doing so we demonstrate the utility of a mathematical graph as an ecological construct with respect to habitat connectivity. Graph theory is a well established mainstay of information technology and is concerned with highly efficient network flow. It employs fast algorithms and compact data structures that are easily adapted to landscape-level focal species analysis. American mink (Mustela vison) and prothonotary warblers (Protonotaria citrea) share the same habitat but have different dispersal capabilities, and therefore provide interesting comparisons on connections in the landscape. We built graphs using GIS coverages to define habitat patches and determined the functional distance between the patches with least-cost path modeling. Using graph operations concerned with edge and node removal we found that the landscape is fundamentally connected for mink and fundamentally unconnected for prothonotary warblers. The advantage of a graph-theoretic approach over other modeling techniques is that it is a heuristic framework which can be applied with very little data and improved from the initial results. We demonstrate the use of graph theory in a metapopulation context, and suggest that graph theory as applied to conservation biology can provide leverage on applications concerned with landscape connectivity.
Article
Methods for selecting sites to be included in reserve networks generally neglect the spatial location of sites, often resulting in highly fragmented networks. This restricts the possibility of dispersal between sites, which for many species may be essential for long-term persistence. Here I describe iterative reserve selection algorithms which incorporate considerations of reserve connectivity and evaluate their performance using a data set for macroinvertebrates in ponds. Methods where spatial criteria were only invoked when ties between sites occurred did not perform significantly better than a simple greedy algorithm in terms of reserve connectivity. An algorithm based on a composite measure of species added and changes in reserve connectivity produced a reserve network with higher connectivity, but needed more sites to represent all species. A trade-off between connectivity and efficiency may be inevitable, but the costs in terms of efficiency may be justified if long-term persistence of species is more likely.
Article
Connectivity is a major concern for the maintenance of wildlife populations, ecological flows, and many other landscape functions. For these reasons many different connectivity indices have been used or proposed for landscape conservation planning; however, their properties and behaviour have not been sufficiently examined and may provide misleading or undesired results for these purposes. We here present a new index (probability of connectivity, PC) that is based on the habitat availability concept, dispersal probabilities between habitat patches and graph structures. We evaluate the performance of PC and compare it with other widespread indices through a set of 13 relevant properties that an index should ideally fulfil for adequately integrating connectivity in landscape planning applications. We found that PC is the only index that systematically accomplished all the requirements, overcoming some serious limitations of other available indices. We encourage the use of PC as a sound basis for planning decision-making. To demonstrate the use and potential of PC for practical landscape applications, we present an example of application to a case study for the goshawk (Accipiter gentilis) in Catalonia (NE Spain), where we identify those habitat areas that most contribute to overall landscape connectivity and evaluate the effectiveness and potential improvement of a protected areas network (Natura 2000) for conserving those critical habitat areas.
Article
The Tibetan Plateau is one of the top 10 biodiversity hotspots in the world and acts as a modern harbour for many rare species because of its relatively pristine state. In this article, we report a landscape genetic study on the Yunnan snub-nosed monkey (Rhinopithecus bieti), a primate endemic to the Tibetan Plateau. DNA was extracted from blood, tissue and fecal samples of 135 wild individuals representing 11 out of 15 extant monkey groups. Ten microsatellite loci were used to characterize patterns of genetic diversity. The most striking feature of the population structure is the presence of five subpopulations with distinct genetic backgrounds and unique spatial regions. The population structure of R. bieti appears to be shaped by anthropogenic landscape features as gene flow between subpopulations is strongly impeded by arable land, highways and human habitation. A partial Mantel test showed that 36.23% (r = 0.51, P = 0.01) of the genetic distance was explained by habitat gaps after controlling for the effect of geographical distance. Only 4.92% of the genetic distance was explained by geographical distance in the partial Mantel test, and no significant correlation was found. Estimation of population structure history indicates that environmental change during the last glacial maximum and human impacts since the Holocene, or a combination of both, have shaped the observed population structure of R. bieti. Increasing human activity on the Plateau, especially that resulting in habitat fragmentation, is becoming an important factor in shaping the genetic structure and evolutionary potential of species inhabiting this key ecosystem.
Article
This article examines the effect of ambient temperature, day length, weather conditions, and seasonality on daily path length (DPL) of a free-ranging group of Yunnan snub-nosed monkeys (Rhinopithecus bieti) using an auto-released GPS collar. Data were collected from December 17, 2003 to October 22, 2004 at Laojunshan in northwestern Yunnan province, China. The average DPL of the monkey group was 909+/-472 m (n=291), with the shortest distance being 180 m and the longest distance 3,626 m. Ambient temperature and day length were found to affect DPL. Both factors were positively correlated with DPL, which means that the monkey group traveled greater distances on longer and warmer days. At the study site, three distinct seasons were identified, and DPL did not vary significantly across these periods. The time of sunrise was not correlated with DPL. Nevertheless, we sometimes observed the group starting its daily trip later on cloudy days than on sunny days. Furthermore, weather conditions (e.g. rainy, cloudy, and sunny) did not influence the average DPL of the study group. Overall we found that the primary factors affecting DPL in R. bieti were day length and ambient temperature, especially daily highest temperature.
Article
Rhinopithecus bieti, the Yunnan snub-nosed monkey, is the nonhuman primate with the highest altitudinal distribution and is also one of the 25 most globally endangered primate species. Currently, R. bieti is found in forests between 3000 and 4500 m above sea level, within a narrow area on the Tibetan Plateau between the Yangtze and Mekong rivers, where it is suffering from loss of habitat and shrinking population size (approximately 1500). To assess the genetic diversity within this species, its population structure and to infer its evolutionary history, we sequenced 401 bp of the hypervariable I (HVI) segment from the mitochondrial DNA control region (CR) for 157 individuals from 11 remnant patches throughout the fragmented distribution area. Fifty-two variable sites were observed and 30 haplotypes were defined. Compared with other primate species, R. bieti cannot be regarded as a taxon with low genetic diversity. Phylogenetic analysis partitioned haplotypes into two divergent haplogroups (A and B). Haplotypes from the two mitochondrial clades were found to be mixed in some patches although the distribution of haplotypes displayed local homogeneity, implying a strong population structure within R. bieti. Analysis of molecular variance detected significant differences among the different geographical regions, suggesting that R. bieti should be separated into three management units (MUs) for conservation. Based on our results, it can be hypothesized that the genetic history of R. bieti includes an initial, presumably allopatric divergence between clades A and B 1.0-0.7 million years ago (Ma), which might have been caused by the Late Cenozoic uplift of the Tibetan Plateau, secondary contact after this divergence as a result of a population expansion 0.16-0.05 Ma, and population reduction and habitat fragmentation in the very recent past.