A model of second-degree Virtual Cut Nodes applied to Complex Networks in Ecological Landscape

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DEVELOPMENT OF A SPATIALY EXPLICIT HABITAT PATCH MODEL (C-PAN) AND COMPARATIVE ANALYSIS OF PATCH MODELING TECHNIQUES: THE CRAFTING OF A NEW TOOL FOR CONSERVATION PLANNERS

ABSTRACT Ecological theories including island biogeography, intermediate disturbance, metapopulation and metacommunity all suggest that habitat patches of larger size and those comprised of substantial configurations of interior or core habitat possess the greatest potential for long-term species viability. As a direct means of mitigating edge encroachment and fragmentation\u27s other adverse effects, there is a growing consensus among conservation planners that assembling larger, more cohesive tracts with substantial core area is of ecological value in conservation planning. Larger and more cohesive patches are believed to sustain larger and more viable local populations, enhance overall biodiversity, incorporate a wider array of natural disturbance regimes, and maintain more vulnerable, specialist species for the long term. Therefore, it is important that size and cohesion metrics be incorporated in patch and reserve modeling and design. This research developed a spatially explicit patch modeling approach designed to incorporate these metrics. This new modeling tool is entitled the Cohesive-Patch Aggregation and Network (C-PAN) model. It was created using ArcMap 9.3 and the Spatial Modeler extension. The model was first tested at a pilot scale (the State of South Carolina) and then up-scaled to evaluate a much larger area (the Northern Appalachian/Acadian Ecoregion). The C-PAN approach is most appropriate for use on species requiring substantial core area and those sensitive to edge characteristics. It is also intended to serve as an alternative approach to heavily parameterized patch modeling methods when species-specific parameterization data are not available. There exist a number of potential benefits associated with C-PAN usage. The C-PAN model searches landscapes for highly cohesive patches with substantial core area within an existing GIS framework. The aggregation and overlay processes used by the model also appeared to be an improvement over highly parameterized approaches which utilize region-growing components for generating patches. Additionally, the Landscape Cohesion Index (LCI) that is generated as part of the patch generation process proved beneficial for measuring fragmentation metrics across multiple sites and landscapes. This may be the first patch modeling approach to use landscape cohesion scores as a means of seeding patches based on their core area composition from the onset of the modeling process. The LCI allows users to delineate patches based on the statistical uniqueness of their core composition. This frees the user from selecting potentially unknown parameter settings when using other more complex approaches. Instead, it allows patches to be delineated and ranked based on how cohesive they are within the landscape. Both of these features may prove attractive to users as they ultimately make the tool more readily accessible to less technical practitioners. The C-PAN model was then used to generate a unique set of patches in the Northern Appalachian/Acadian Ecoregion. C-PAN was then compared to two ArcGIS (v9.3) based commonly used patch generation tools. The tools, Corridor Designer (v1) and FunConn (v1) were used for this analysis because they represent two highly utilized approaches which are most similar to the C-PAN model in both modeling mechanics and process. The patch outputs from the three tools were then compared and evaluated. This analysis was aimed at addressing a void within the literature of comparing the results of multiple patch modeling approaches. This analysis also served as a means of validating the C-PAN approach by comparing patch outputs of the three approaches. C-PAN performed well when compared to the existing patch modeling tools of Corridor Design and FunConn. For all of the spatial and target capture metrics measured, C-PAN ranked first or second among all approaches. The results indicated that the C-PAN patch modeling approach performed as well, and better, in the patch metrics evaluated here (patch area, edge/area ratios, average nearest neighbor, average Human Footprint (HF) score, Last of the Wild (LOW) capture, and patch commission. At relatively high patch selectiveness, the outputs of C-PAN and Corridor design were the most similar in size and distribution across the ecoregion-scale study area. Furthermore, of the three patch delineation tools, C-PAN appears to provide users with greater site discrimination capabilities than Corridor Design or FunConn. This resulted in providing users with a more selective set of discrete patches than the FunConn approach. Both C-PAN and Corridor Design were effective in delineating highly homogenous patches. These results indicate that the C-PAN patch modeling approach outperforms Corridor Designer and FunConn when measures of patch cohesion and core area are of importance. A graph theory based connectivity analysis was then conducted in order to identify and compare linkages between patches from the three patch modeling scenarios. The landscape networks modeled for each of the three scenarios indicated that while local connectivity in portions of the ecoregion may exist, widespread connectivity across the ecoregion as a whole was less likely. This was apparent in the C-PAN and Corridor Design patch scenarios, as multiple connections were delineated across the majority of the study area. Alternatively, no connections were delineated linking portions of the large graphs located within the central portion of the ecoregion with smaller and more linear graphs located in the periphery of the region. This was attributable to natural bottlenecks and relatively high Human Footprint (HF) values in those potential linkage areas. The landscape network derived as part of the FunConn patch scenario indicated even further diminished connectivity within portions of the ecoregion. The C-PAN patch network scenario was comprised of the greatest number of patches. This ultimately resulted in the delineation of multiple and potentially functional redundancies in the landscape network. Increasing the number of patches also improved distance metrics within the minimum spanning tree for this scenario. More patches served as intermediate stepping stones which resulted in shorter linkage and edge lengths and smaller average area corridor requirements. The FunConn patch landscape network however connected significantly fewer patches. This resulted in the longest linkage and edge distances and the largest average corridors within the ecoregion. This represents an apparent tradeoff between the number of potentially beneficial redundant connections and total landscape network corridor area. While more connections may contribute to increased landscape connectivity and landscape function, the increased area requirement make it more costly to implement. On the other hand, fewer connections may be less costly from an implementation standpoint, but may also reduce landscape connectivity and ecological function. The landscape networks were then used to test a simplifying assumption often used in conservation planning: that coarse-scale corridors may provide overlapping or \u27umbrella\u27 effects for other scenarios. This was accomplished by conducting an analysis of corridor overlap among these three scenarios. This work is among the first corridor gap analyses to be conducted at the ecoregion-scale. The corridor gap analysis indicated that 5% of the corridor area for all 3 scenarios was spatially coincident, 34% was coincident over 2 scenarios, while the majority of corridor area (59%) was non-redundant. These results are intriguing for two reasons. First, this gap analysis proved to be a useful tool in identifying potential priority conservation areas. Areas held in common may prove to be no-regret areas for conservation action as they provide overlapping coverage across multiple conservation scenarios. Second, the significant coverage gaps among corridors from these three scenarios indicates that selecting \u27what\u27 to connect at the ecoregion-scale has significant implications for selected corridors. As there was so little modeled corridor area in common among scenarios, there is little reason to believe alternate corridors would be functionally equivalent. This indicates that connecting any one set of habitat nodes would not likely serve as a corridor umbrella for all other scenarios. The ecoregion-scale connectivity analysis conducted here was also useful in flagging areas for conservation prioritization based on their connectivity role within an ecoregion-scale context. Connectivity analysis at this scale may also prove useful for evaluating connectivity at local scales. Any one of the subgraphs found within these modeled landscape networks could help inform local scale conservation efforts. Similarly, local scale connectivity and conservation actions could be added to the ecoregion-scale landscape network. As with many things, a successful landscape network is made up of the sum of its locally implemented parts. Of additional interest, the large size and area requirements of ecoregion-scale corridors may prove to be potential mechanisms by which landscape scale gradients and processes can be included within present day networks of protected lands. While this research did not explore this explicitly, ecoregion-scale corridors may prove to be a provocative means by which natural disturbance regimes, environmental gradients, and shifting species ranges may be captured in conservation networks by virtue of their large size. As such, it may be worth considering ecoregion-scale corridors as implementable conservation components that may facilitate planning for persistence in the face of global climate change

Assessment of ecological connectivity for urban environments: A multispecies approach

The habitats of many ground-based fauna species in developing urban regions have altered in their structure and are often isolated from other habitat locations due to the urban growth. Habitat areas that are well connected to other fragments of habitat have been shown to assist particular fauna in their movement from one location to another. Two key benefits of faunal movement are the transfer of genes resulting in improved genetic diversity and support for larger populations of particular species. Habitat connectivity is therefore seen as critical to the survival of many fauna species in urban locations. Lack of habitat connectivity in the landscape poses the critical threat of extinction to many ground-based species. This thesis develops a multispecies method for assessing habitat connectivity in urban landscapes. While effective conservation management requires a multispecies approach to establishing conservation priorities, connectivity is in fact a species-specific attribute of the landscape. This study aims to assess connectivity by developing a multispecies method based on species-specific considerations, thereby addressing the differences in the two aspects. The application of graph theory is well suited to modelling the structure of urban landscapes. A graph-based multispecies method was designed based on specific criteria relating to a biologically realistic assessment of connectivity. This was then applied to Metropolitan Melbourne by determining the habitat networks of four ground-based fauna species and assessing connectivity across species networks. The method was then evaluated by testing the sensitivity of modelling outputs to the determination of the maximum effective distance for the target species and the resistance values that were used to quantify the species resistance layers. The species-specific connectivity outcomes were then overlaid and combined in order to assess overall ecological connectivity. The revised method comprises four key steps. These are: (1) choice of target species for a given urban region; (2) construction of species-specific networks within that region; (3) connectivity measurement of species-specific networks; and (4) combination of connectivity results to assess the ecological connectivity for the urban region. In general, this study offers three innovations. First, the graph-based multispecies method is innovative in terms of multispecies capacity to consider species-specific characteristics when assessing connectivity. Second, it establishes a rigorous set of graph-based metrics that determine essential dimensions of connectivity: connectivity between two specific habitats, connectivity of the whole network, and those habitats that contribute most to connectivity. Third, the study developed a new algorithm for the identification of gaps in species habitat networks. In addition, the method offers new insights into the development of species-specific resistance layers. The multispecies method allows for flexibility in decision-making by providing opportunities for trade-offs between different conservation alternatives. The method will serve as a foundation to support conservation planning and decision-making through the establishment of priority areas within the urban landscape that will enhance connectivity and support biodiversity. This multispecies method will assist any conservation authority to avoid redundancy in planning and decision-making, thereby ensuring long-term financial savings in conservation projects

Modelação geográfica da fragmentação e conectividade de habitats: casos de estudo nos padrões de distribuição local de espécies selvagens

Habitat fragmentation and the resultant reduction in connectivity are process of major importance in the persistence and patterns distribution of wildlife species. This thesis focuses on habitat fragmentation and connectivity, assessing their consequences on the local patterns distribution of wildlife species. The cases studies were published and conducted with monitoring data systematized using a common database. The case studies were located in the Alentejo region between the years of 1995 and 2005. The case studies are supported by examples of local impacts of fragmentation on the habitat connectivity of birds and reptile species patterns distribution. The observed pattern-process interactions are assessing by geographic modeling techniques. Methodologies were developed based on the innovative application of spatial statistical and networks analysis. The results show that the geographic modeling represents an added value to the understanding pattern-process interactions. The findings show how much the local distribution patterns of individuals are affected by habitat disturbances; RESUMO: A fragmentação dos habitats e a conectividade são processos de importância maior na persistência e nos padrões de distribuição das espécies selvagens. Esta tese centra -se na avaliação da fragmentação e conectividade dos habitats nos padrões locais de distribuição de espécies selvagens. Para tal foram realizados casos de estudo, com dados relativos a monitorizações efectuadas no Alentejo entre os anos de 1995 e 2005 e sistematizados numa base dados. Os casos de estudo foram publicados e são suportados por exemplos de impactes locais no padrão de distribuição de espécies de aves e réptil. Foram utilizadas técnicas de modelação geográfica na descrição e avaliação dos processos e padrões observados. Aplicadas e desenvolvidas metodologias inovadoras, com o suporte de técnicas de estatística espacial e análise de redes. Os resultados mostram que a modelação geográfica representa uma maisvalia para a compreensão da dinâmica entre padrões-processos. Os resultados revelam o quanto, os padrões de distribuição local dos indivíduos são afectados pelas alterações nos habitats

Quantifying landscape connectivity using probability of connectivity response curves

Maintenance of habitat connectivity is recommended as a method of promoting biodiversity. A systematic manipulation of a simple theoretical landscape was used to assess how a landscape connectivity index responded to specific changes in habitat distribution. Quantifying the response of the index to changes in the spatial scale of dispersal is proposed as a method of objectively quantifying multiple aspects of landscape structure known to influence habitat connectivity. An ecosystem simulation model was used to assess if the index demonstrated the same patterns of response to changes in complex landscapes, and to quantify impact of logging distribution, roads, natural disturbances and habitat corridors. The high degree of sensitivity to the presence of roads, and the scale of response to different management scenarios highlight the value of the proposed index, and the sensitivity to the assumptions of habitat delineation used in index calculation.connectivitylandscape ecologyforestrybiodiversit

Quantifying landscape connectivity using probability of connectivity response curves

Maintenance of habitat connectivity is recommended as a method of promoting biodiversity. A systematic manipulation of a simple theoretical landscape was used to assess how a landscape connectivity index responded to specific changes in habitat distribution. Quantifying the response of the index to changes in the spatial scale of dispersal is proposed as a method of objectively quantifying multiple aspects of landscape structure known to influence habitat connectivity. An ecosystem simulation model was used to assess if the index demonstrated the same patterns of response to changes in complex landscapes, and to quantify impact of logging distribution, roads, natural disturbances and habitat corridors. The high degree of sensitivity to the presence of roads, and the scale of response to different management scenarios highlight the value of the proposed index, and the sensitivity to the assumptions of habitat delineation used in index calculation.connectivitylandscape ecologyforestrybiodiversit

Criteria for Modification of Complex Infrastructure Networks

Complex network theory enables the analysis and comparison of graphs with a very large number of nodes, or with non-trivial topological properties. Graph models exist for many kinds of networks, ranging from computer networks to representation of protein-protein interactions, and analysis techniques are often shared between fields of application. Infrastructure networks are an active field of application of complex network analysis, which is frequently aimed at finding ways to improve on the structure of a network, while respecting budget constraints. In this activity, complex network analysis is often cross-referenced with simulations or operational research. Power grids stand out among the most prominent examples of infrastructure network analyzed with techniques derived from complex network theory, due to their importance as a service, their properties of quick response to events, and the desired transition to a smart grid paradigm. With the growing interest for the protection of endangered species and habitats, the modeling and analysis of green infrastructure has also received increasing attention from scholars. These classes of infrastructure provide case studies for the exemplification of a common process for the analysis of various kinds of infrastructure networks, which involves the identification of vulnerabilities, the exploration of a search space for possible modifications, and the definition of a comparable measure of health of the network.Complex network theory enables the analysis and comparison of graphs with a very large number of nodes, or with non-trivial topological properties. Graph models exist for many kinds of networks, ranging from computer networks to representation of protein-protein interactions, and analysis techniques are often shared between fields of application. Infrastructure networks are an active field of application of complex network analysis, which is frequently aimed at finding ways to improve on the structure of a network, while respecting budget constraints. In this activity, complex network analysis is often cross-referenced with simulations or operational research. Power grids stand out among the most prominent examples of infrastructure network analyzed with techniques derived from complex network theory, due to their importance as a service, their properties of quick response to events, and the desired transition to a smart grid paradigm. With the growing interest for the protection of endangered species and habitats, the modeling and analysis of green infrastructure has also received increasing attention from scholars. These classes of infrastructure provide case studies for the exemplification of a common process for the analysis of various kinds of infrastructure networks, which involves the identification of vulnerabilities, the exploration of a search space for possible modifications, and the definition of a comparable measure of health of the network

Investigating the great crested newt landscape in a pond rich environment : developing a landscape scale management perspective

This thesis investigated graph theoretic analysis of connectivity and habitat availability for landscape scale management of Triturus cristatus, the Great Crested Newt. The ecological foundations of wider landscape management concepts and knowledge base on T. cristatus' habitat requirements, dispersal and migration were explored. Species presence, and aquatic and terrestrial habitat on the Cholmondeley Estate, Malpas, Cheshire, UK was mapped and land cover characterized for suitability and traversibility by T. cristatus. Habitat area available and accessible from ponds were identified. Analysis and modelling of pondscape connectivity using Probability of Connectivity (PC) and related indices, was carried out using Euclidean and Cost Weighted Distance and pond clustering at ecologically relevant scales was examined. Association or correlation of presence with proximity to breeding ponds, pond cluster size, proximity and available quantity of terrestrial habitat, proximity to roads and moving water, and connectivity of breeding ponds were examined at Cost Weighted and Euclidean distances. Connectivity, (PC index), pond count in clusters at 250 and 500m thresholds of connectivity, and proximity to core habitat (broad leaved woodland and rough grassland) using Cost Weighted distances were positively associated with breeding presence. Road proximity and density, proximity of core habitat at Euclidean distances and mean inter-pond distance were not significantly associated with breeding presence. Proximity to moving water was negatively associated with breeding presence. Resistance to movement of various land cover types has important implications for habitat availability and connectivity, , / and important questions are raised in terms of "rule of thumb" guidelines for estimation of connectivity between pond populations and habitat availability around breeding ponds. Graph analysis was used to identify priority areas for maintenance of landscape level connectivity, and enhancement of habitat connectivity and availability on the local population scale, with prioritization of pond creation/protection sites against their contribution to connectivity and habitat I availability, examining various scenarios