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1.
Jordán  F.  Báldi  A.  Orci  K.-M.  Rácz  I.  Varga  Z. 《Landscape Ecology》2003,18(1):83-92
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.This revised version was published online in May 2005 with corrections to the Cover Date.  相似文献   

2.
Maintaining connectivity among local populations in a fragmented landscape is crucial for the survival of many species. For isolated habitat patches, stochastic fluctuations and reduced gene flow can lead to high risk of extinction. The connectivity of the landscape is especially crucial for the carabid species living in the fragmented forests of the Bereg plain (NE Hungary and W Ukraine) because a highway will be constructed through the plain. Our purpose is to (1) evaluate the impacts of three possible highway tracks, (2) suggest a solution that is realistic with less impact on connectivity than other plans and (3) discuss how to decrease the disadvantageous effects of each track. Our results, based on a network analysis of landscape graph of patches and ecological corridors, indicate that the intended highway could have deleterious consequences on forest-living carabids. Relatively simple actions, like the establishment of stepping stones, could compensate for the loss of habitat connectivity and promote the survival of carabids, or minor modifications in one possible track could diminish its adverse effects. While many other studies would be needed for a comprehensive assessment of the biotic impact of the highway, we provide an example on the usefulness of network analysis for land use management. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

3.
The loss of connectivity of natural areas is a major threat for wildlife dispersal and survival and for the conservation of biodiversity in general. Thus, there is an increasing interest in considering connectivity in landscape planning and habitat conservation. In this context, graph structures have been shown to be a powerful and effective way of both representing the landscape pattern as a network and performing complex analysis regarding landscape connectivity. Many indices have been used for connectivity analyses so far but comparatively very little efforts have been made to understand their behaviour and sensitivity to spatial changes, which seriously undermines their adequate interpretation and usefulness. We systematically compare a set of ten graph-based connectivity indices, evaluating their reaction to different types of change that can occur in the landscape (habitat patches loss, corridors loss, etc.) and their effectiveness for identifying which landscape elements are more critical for habitat conservation. Many of the available indices were found to present serious limitations that make them inadequate as a basis for conservation planning. We present a new index (IIC) that achieves all the properties of an ideal index according to our analysis. We suggest that the connectivity problem should be considered within the wider concept of habitat availability, which considers a habitat patch itself as a space where connectivity exists, integrating habitat amount and connectivity between habitat patches in a single measure.  相似文献   

4.
Connectivity models using empirically-derived landscape resistance maps can predict potential linkages among fragmented animal and plant populations. However, such models have rarely been used to guide systematic decision-making, such as identifying the most important habitat patches and dispersal corridors to protect or restore in order to maximize regional connectivity. Combining resistance models with network theory offers one means of prioritizing management for connectivity, and we applied this approach to a metapopulation of desert bighorn sheep (Ovis canadensis nelsoni) in the Mojave Desert of the southwestern United States. We used a genetic-based landscape resistance model to construct network models of genetic connectivity (potential for gene flow) and demographic connectivity (potential for colonization of empty habitat patches), which may differ because of sex-biased dispersal in bighorn sheep. We identified high-priority habitat patches and corridors and found that the type of connectivity and the network metric used to quantify connectivity had substantial effects on prioritization results, although some features ranked highly across all combinations. Rankings were also sensitive to our empirically-derived estimates of maximum effective dispersal distance, highlighting the importance of this often-ignored parameter. Patch-based analogs of our network metrics predicted both neutral and mitochondrial genetic diversity of 25 populations within the study area. This study demonstrates that network theory can enhance the utility of landscape resistance models as tools for conservation, but it is critical to consider the implications of sex-biased dispersal, the biological relevance of network metrics, and the uncertainty associated with dispersal range and behavior when using this approach.  相似文献   

5.
This study investigated the efficacy of linear landscape elements in fragmented landscapes as corridors for perennial grassland species with short-range seed dispersal. Corridors are assumed to be essential for the persistence of metapopulations in fragmented landscapes, but it is unclear to what extent linear landscape elements such as ditch banks and road verges can function as corridors for those species. The principal factors that determine the rate of migration through corridors include the width and habitat quality of patches within a corridor (expressed as the population growth rate λ) and the dispersal capacity of plants (expressed as the slope α of the relationship between seed number and log-distance). A cellular automation model was used to simulate the effects of the principal factors on the rate of migration. Simulations with different levels of the principal factors showed highly significant and positive main effects of dispersal capacity, habitat quality and width of corridors on the migration rate. Significant interactions existed between dispersal capacity × width and dispersal capacity × habitat quality (p<0.0001), indicating that the effects of width and habitat quality depended on the dispersal capacity. In narrow corridors most of the dispersed seeds were deposited outside the corridor, which significantly reduced migration rates, especially for species with long-range dispersal (α=−0.4). In wide corridors (up to 20 m), seed losses were much smaller and migration rates approximated those of continuous habitats. The contribution of the few long-range seeds to the rate of migration was significant when habitat quality was high (population growth rates up to 2.5). However, in all simulations migration rates were very low,i.e.<5 m/yr. It is concluded that linear landscape elements are not effective corridors in fragmented landscapes for plants with short-range seed dispersal, because migration rates are low (<5 m/yr), landscape elements vary in the percentage of high quality patches, and refugia and suitable habitat patches are frequently several kilometres apart, making a cohesive infrastructure of corridors for plants elusive. It is argued that the best way to conserve endangered plant species that encounter dispersal barriers is to harvest seeds from nearby source populations and introduce them as suitable habitats.  相似文献   

6.
Anthropogenic modification of the countryside has resulted in much of the landscape consisting of fragments of once continuous habitat. Increasing habitat connectivity at the landscape-scale has a vital role to play in the conservation of species restricted to such remnant patches, especially as species may attempt to track zones of habitat that satisfy their niche requirements as the climate changes. Conservation policies and management strategies frequently advocate corridor creation as one approach to restore connectivity and to facilitate species movements through the landscape. Here we examine the utility of hedgerows as corridors between woodland habitat patches using rigorous systematic review methodology. Systematic searching yielded 26 studies which satisfied the review inclusion criteria. The empirical evidence currently available is insufficient to evaluate the effectiveness of hedgerow corridors as a conservation tool to promote the population viability of woodland fauna. However, the studies did provide anecdotal evidence of positive local population effects and indicated that some species use hedgerows as movement conduits. More replicated and controlled field investigations or long-term monitoring are required in order to allow practitioners and policy makers to make better informed decisions about hedgerow corridor creation and preservation. The benefits of such corridors in regard to increasing habitat connectivity remain equivocal, and the role of corridors in mitigating the effects of climate change at the landscape-scale is even less well understood.  相似文献   

7.
Many organisms persist in fragmented habitat where movement between patches is essential for long-term demographic and genetic stability. In the absence of direct observation of movement, connectivity or isolation metrics are useful to characterize potential patch-level connectivity. However, multiple metrics exist at varying levels of complexity, and empirical data on species distribution are rarely used to compare performance of metrics. We compared 12 connectivity metrics of varying degrees of complexity to determine which metric best predicts the distribution of prairie dog colonies along an urban gradient of 385 isolated habitat patches in Denver, Colorado, USA. We found that a modified version of the incidence function model including area-weighting of patches and a cost-weighted distance surface best predicted occupancy, where we assumed roads were fairly impermeable to movement, and low-lying drainages provided dispersal corridors. We also found this result to be robust to a range of cost weight parameters. Our results suggest that metrics should incorporate both patch area and the composition of the surrounding matrix. These results provide guidance for improved landscape habitat modeling in fragmented landscapes and can help identify target habitat for conservation and management of prairie dogs in urban systems.  相似文献   

8.
Graph-based analysis is a promising approach for analyzing the functional and structural connectivity of landscapes. In human-shaped landscapes, species have become vulnerable to land degradation and connectivity loss between habitat patches. Movement across the landscape is a key process for species survival that needs to be further investigated for heterogeneous human-dominated landscapes. The common frog (Rana temporaria) was used as a case study to explore and provide a graph connectivity analysis framework that integrates habitat suitability and dispersal responses to landscape permeability. The main habitat patches influencing habitat availability and connectivity were highlighted by using the software Conefor Sensinode 2.2. One of the main advantages of the presented graph-theoretical approach is its ability to provide a large choice of variables to be used based on the study’s assumptions and knowledge about target species. Based on dispersal simulation modelling in potential suitable habitat corridors, three distinct patterns of nodes connections of differing importance were revealed. These patterns are locally influenced by anthropogenic barriers, landscape permeability, and habitat suitability. And they are affected by different suitability and availability gradients to maximize the best possible settlement by the common frog within a terrestrial habitat continuum. The study determined the key role of landscape-based approaches for identifying the “availability-suitability-connectivity” patterns from a local to regional approach to provide an operational tool for landscape planning.  相似文献   

9.
We introduce a novel approach to building corridors in spatial conservation prioritization. The underlying working principle is the use of a penalty structure in an iterative algorithm used for producing a spatial priority ranking. The penalty term aims to prevent loss or degradation of structural connections, or, equivalently, to promote to a higher rank landscape elements that are required to keep networks connected. The proposed method shows several convenient properties: (1) it does not require a priori specification of habitat patches, end points or related thresholds, (2) it does not rely on resistance coefficients for different habitats, (3) it does not require species targets, and (4) the cost of additional connectivity via corridors can be quantified in terms of habitat quality lost across species. Corridor strength and width parameters control the trade-off between increased structural connectivity via corridors and other considerations relevant to conservation planning. Habitat suitability or dispersal suitability layers used in the analysis can be species specific, thus allowing analysis both in terms of structural and functional connectivity. The proposed method can also be used for targeting habitat restoration, by identifying areas of low habitat quality included in corridors. These methods have been implemented in the Zonation software, and can be applied to large scale and high resolution spatial prioritization, effectively integrating corridor design and spatial conservation prioritization. Since the method operates on novel principles and combines with a large number of features already operational in Zonation, we expect it to be of utility in spatial conservation planning.  相似文献   

10.
Context

Modifications in natural landcover generally result in a loss of habitat availability for wildlife and it’s persistence will depend largely on their spatial configuration and functional connections. Argenteohyla siemersi is a threatened and endemic amphibian whose habitat is composed of forest patches near rivers and water bodies edges.

Objectives

This study aimed to analyse the accessible habitat for this species and identify key elements to maintain its ecological network in two different types of land uses: an anthropized area with extensive cattle raising and a protected area.

Methods

The structural and functional characteristics of both landscapes were analyzed. The connectivity at landscape level and the contribution of each habitat patch were evaluated through simulation models with different dispersion distances in the context of the graph theory.

Results

In both landscapes, nine types of landcover were identified with different compositions. Remarkable differences were found in habitat connectivity for this amphibian species between both landscapes. As the percentage of dispersion distance increases, reachable habitat increases as well, although with higher percentages in the protected area. Two corridors were identified in the protected landscape and one in the rangeland one; patches and key links constituted all of them.

Conclusions

The present work provides spatially explicit results with a quantitative basis. It could be useful as a tool for the development of management plans aimed at guaranteeing the functionality of the ecological network for this endangered species and, therefore, contribute to its long-term conservation.

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11.
Loss of connectivity is one of the main causes of decreases in habitat availability and, thus, in species abundance and occurrence in fragmented landscapes. It is therefore important to measure habitat connectivity for conservation purposes, but there are several difficulties in quantifying connectivity, including the need for species movement behavioral data and the existence of few consistent indices to describe such data. In the present study, we used a graph theoretical framework to measure habitat availability, and we evaluate whether this variable is adequate to explain the occurrence pattern of an Atlantic rainforest bird (Pyriglena leucoptera, Thamnophilidae). The playback technique was used to parameterize the connectivity component of habitat availability indices and to determine the presence or absence of the study species in forest patches. Patch- and landscape-level habitat availability indices were considered as explanatory variables. Two of these were landscape-level indices, which varied in terms of how inter-patch connections are defined, using either a binary or probabilistic approach. This study produced four striking results. First, even short open gaps may disrupt habitat continuity for P. leucoptera. Second, the occurrence of P. leucoptera was positively affected by habitat availability. Third, proper measures of this explanatory variable should account for the landscape context around the focal patch, emphasizing the importance of habitat connectivity. Finally, habitat availability indices should consider probabilistic and not binary inter-patch connections when intending to explain the occurrence of bird species in fragmented landscapes. We discuss some conservation implications of our results, stressing the advantages of an ecologically scaled graph theoretical framework.  相似文献   

12.
Landscape ecologists have increasingly turned to the use of landscape graphs in which a landscape is represented as a set of nodes (habitat patches) connected by links representing inter-patch-dispersal. This study explores the use of a graph-based regionalization method, Graph-based REgionalization with Clustering And Partitioning (GraphRECAP), to detect structural groups of habitat patches (compartments) in a landscape graph such that the connections (i.e. the movement of individual organisms) within the groups are greater than those across groups. Specifically, we mapped compartments using habitat and dispersal data for ring-tailed lemurs (Lemur catta) in an agricultural landscape in southern Madagascar using both GraphRECAP and the widely-used Girvan and Newman method. Model performance was evaluated by comparing compartment characteristics and three measures of network connectivity and traversability: the connection strength of habitat patches in the compartments (modularity), the potential ease of individual organism movements (Harary index), and the degree of alternative route presence (Alpha index). Compartments identified by GraphRECAP had stronger within-compartment connections, greater traversability, more alternative routes, and a larger minimum number of habitat patches within compartments, all of which are more desirable traits for ecological networks. Our method could thus facilitate the study of ecosystem resilience and the design of nature reserves and landscape networks to promote the landscape-scale dispersal of species in the fragmented habitats.  相似文献   

13.
Connectivity measures: a review   总被引：8，自引：3，他引：5  
One of the central problems in contemporary ecology and conservation biology is the drastic change of landscapes induced by anthropogenic activities, resulting in habitat loss and fragmentation. For many wild living species, local extinctions of fragmented populations are common and recolonization is critical for regional survival. Successful recolonization depends on the availability of dispersing individuals and the degree of landscape connectivity. The obvious implications of landscape connectivity for conservation biology have led to a proliferation of connectivity measures. However, general relationships between landscape connectivity and landscape structure are lacking, and so are the relationships between different connectivity metrics. Consequently, there is a need to develop landscape metrics that more accurately characterize the landscape with an emphasis on the underlying processes. Here we review various definitions of landscape connectivity, explain their mathematical connotations, and make some unifying conclusions and suggestions for future research.  相似文献   

14.
Spatial graphs in landscape ecology and conservation have emerged recently as a powerful methodology to model patterns in the topology and connectivity of habitat patches (structural connectivity) and the movement of genes, individuals or populations among these patches (potential functional connectivity). Most spatial graph’s applications to date have been in the terrestrial realm, whereas the use of spatially explicit graph-based methods in the freshwater sciences has lagged far behind. Although at first patch-based spatial graphs were not considered suitable for representing the branching network of riverine landscapes, here we argue that the application of graphs can be a useful tool for quantifying habitat connectivity of freshwater ecosystems. In this review we provide an overview of the potential of patch-based spatial graphs in freshwater ecology and conservation, and present a conceptual framework for the topological analysis of stream networks (i.e., riverscape graphs) from a hierarchical patch-based context. By highlighting the potential application of graph theory in freshwater sciences we hope to illustrate the generality of spatial network analyses in landscape ecology and conservation.  相似文献   

15.
Predicting the vulnerability of landscapes to both the initial colonisation and the subsequent spread of invasive species remains a major challenge. The aim of this study was to assess the relative importance of sub-patch level factors and landscape factors for the invasion of the megaforb Heracleum mantegazzianum. In particular, we tested which factors affect the presence in suitable habitat patches and the cover-percentage within invaded patches. For this purpose, we used standard (logistic) regression modelling techniques. The regression analyses were based on inventories of suitable habitat patches in 20 study areas (each 1 km2) in cultural landscapes of Germany. The cover percentage in invaded patches was independent from landscape factors, except for patch shape, and even unsatisfactorily explained by sub-patch level factors included in the analysis (R 2 = 0.19). In contrast, presence of H. mantegazzianum was affected by both local and landscape factors. Woody habitat structure decreased the occurrence probability, whereas vicinity to transport corridors (rivers, roads), high habitat connectivity, patch size and perimeter-area ratio of habitat patches had positive effects. The significance of corridors and habitat connectivity shows that dispersal of H. mantegazzianum through the landscape matrix is limited. We conclude that cultural landscapes of Germany function as patch-corridor-matrix mosaics for the spread of H. mantegazzianum. Our results highlight the importance of landscape structure and habitat configuration for invasive spread. Furthermore, this study shows that both local and landscape factors should be incorporated into spatially explicit models to predict spatiotemporal dynamics and equilibrium stages of plant invasions.  相似文献   

16.
In this paper we show how the spatialconfiguration of habitat quality affects the spatial spread of apopulation in a heterogeneous environment. Our main result is thatfor species with limited dispersal ability and a landscape withisolated habitats, stepping stone patches of habitat greatlyincrease the ability of species to disperse. Our results showthat increasing reproductive rate first enables and thenaccelerates spatial spread, whereas increasing the connectivity has aremarkable effect only in case of low reproductive rates. Theimportance of landscape structure varied according to thedemographic characteristics of the population. To show this wepresent a spatially explicit habitat model taking into accountpopulation dynamics and habitat connectivity. The population dynamicsare based on a matrix projection model and are calculated on eachcell of a regular lattice. The parameters of the Leslie matrix dependon habitat suitability as well as density. Dispersal between adjacentcells takes place either unrestricted or with higher probability inthe direction of a higher habitat quality (restricted dispersal).Connectivity is maintained by corridors and stepping stones ofoptimal habitat quality in our fragmented model landscape containinga mosaic of different habitat suitabilities. The cellular automatonmodel serves as a basis for investigating different combinations ofparameter values and spatial arrangements of cells with high and lowquality.This revised version was published online in May 2005 with corrections to the Cover Date.  相似文献   

17.
The distribution of the northern brown bandicoot (Isoodon macrourus), a medium-sized ground-dwelling marsupial, was examined in habitat fragments within the urban landscape of the city of Brisbane, Australia. From surveys conducted in 68 fragments, bandicoots were found to be present in 33 (49%) despite widespread habitat loss and fragmentation. Logistic regression analysis revealed that of 13 measured independent variables, functional connectivity was the only factor that significantly predicted the presence of bandicoots within fragments, with connectivity positively correlated with the likelihood of occupation. Functional connectivity was equated to the likelihood of bandicoot immigration into the focal fragment from the nearest occupied fragment, based on the estimated resistance to movement offered by the intervening matrix. Within Brisbane, riparian habitat fragments typically have a relatively high level of functional connectivity, as thin strips of vegetation fringing waterways serve as corridors between larger riparian areas and facilitate the movement of bandicoots between patches. Analyses based on the Akaike Information Criterion revealed that the optimal model based on landscape context variables was convincingly better supported by the data than the optimal model produced from fragment characteristics. However, it is important to examine both internal attributes of habitat fragments and external features of the surrounding landscape when modelling the distribution of ground-dwelling fauna in urban environments, or other landscapes with a highly variable matrix. As urban centres throughout the world expand, it is crucial that the ecology of local wildlife be considered to ensure functional connection is maintained between habitat patches, especially for the conservation of species that are highly susceptible to fragmentation.  相似文献   

18.
Assessing landscape connectivity is important to understand the ecology of landscapes and to evaluate alternative conservation strategies. The question is though, how to quantify connectivity appropriately, especially when the information available about the suitability of the matrix surrounding habitat is limited. Our goal here was to investigate the effects of matrix representation on assessments of the connectivity among habitat patches and of the relative importance of individual patches for the connectivity within a habitat network. We evaluated a set of 50 × 50 km2 test areas in the Carpathian Mountains and considered three different matrix representations (binary, categorical and continuous) using two types of connections among habitat patches (shortest lines and least-cost paths). We compared connections, and the importance of patches, based on (1) isolation, (2) incidence-functional, and (3) graph measures. Our results showed that matrix representation can greatly affect assessments of connections (i.e., connection length, effective distance, and spatial location), but not patch prioritization. Although patch importance was not much affected by matrix representation, it was influenced by the connectivity measure and its parameterization. We found the biggest differences in the case of the integral index of connectivity and equally weighted patches, but no consistent pattern in response to changing dispersal distance. Connectivity assessments in more fragmented landscapes were more sensitive to the selection of matrix representation. Although we recommend using continuous matrix representation whenever possible, our results indicated that simpler matrix representations can be also used as a proxy to delineate those patches that are important for overall connectivity, but not to identify connections among habitat patches.  相似文献   

19.
Context

Graph-theoretic evaluations of habitat connectivity often rely upon least-cost path analyses to evaluate connectedness of habitat patches, based on an underlying cost surface. We present two improvements upon these methods.

Objectives

As a case study to test these methods, we evaluated habitat connectivity for the endangered San Martin titi monkey (Plecturocebus oenanthe) in north-central Peru, to prioritize habitat patches for conservation.

Methods

First, rather than using a single least-cost path between habitat patches, we analyzed multigraphs made up of multiple low-cost paths. This allows us to differentiate between patches connected through a single narrow corridor, and patches connected by a wide swath of traversable land. We evaluate potential movement pathways by iteratively removing paths and recomputing connectivity metrics. Second, instead of performing a sensitivity analysis by varying costs uniformly across the landscape, we generated landscapes with spatially varying costs.

Results

This approach produced a more informative assessment of connectivity than standard graph analyses. Of the 4340 habitat patches considered across the landscape, we identified the most important 100, those frequently ranked highly through repeated network modifications, for multiple metrics and cost surfaces.

Conclusions

These methods represent a novel approach for assessing connectivity, better accounting for spatial configurations of habitat patches and uncertainty in cost surfaces. The ability to identify habitat patches with more possible routes to other patches is of interest for resiliency planning and prioritization in the face of continued habitat loss and climate change. These methods should be broadly applicable to conservation planning for other wildlife species.

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20.
Animal behavior, cost-based corridor models, and real corridors   总被引：2，自引：1，他引：1  
Corridors are popular conservation tools because they are thought to allow animals to safely move between habitat fragments, thereby maintaining landscape connectivity. Nonetheless, few studies show that mammals actually use corridors as predicted. Further, the assumptions underlying corridor models are rarely validated with field data. We categorized corridor use as a behavior, to identify animal-defined corridors, using movement data from fishers (Martes pennanti) tracked near Albany, New York, USA. We then used least-cost path analysis and circuit theory to predict fisher corridors and validated the performance of all three corridor models with data from camera traps. Six of eight fishers tracked used corridors to connect the forest patches that constitute their home ranges, however the locations of these corridors were not well predicted by the two cost-based models, which together identified only 5 of the 23 used corridors. Further, camera trap data suggest the cost-based corridor models performed poorly, often detecting fewer fishers and mammals than nearby habitat cores, whereas camera traps within animal-defined corridors recorded more passes made by fishers, carnivores, and all other non-target mammal groups. Our results suggest that (1) fishers use corridors to connect disjunct habitat fragments, (2) animal movement data can be used to identify corridors at local scales, (3) camera traps are useful tools for testing corridor model predictions, and (4) that corridor models can be improved by incorporating animal behavior data. Given the conservation importance and monetary costs of corridors, improving and validating corridor model predictions is vital.  相似文献   

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