Habitat Models for Population Viability Analysis
Determining what constitutes a suitable habitat for different species is a fundamental part of applied ecology and is the core component of many conservation planning strategies. Information on habitat availability underpins efforts to assess the threats
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8.1 Introduction Determining what constitutes a suitable habitat for different species is a fundamental part of applied ecology and is the core component of many conservation planning strategies. Information on habitat availability underpins efforts to assess the threats faced by species and to determine the adequacy of conservation reserves (e.g. Margules et al. 1988). Expert rules are often used to categorize the response of a species to changes in available habitat (e.g. Millsap et al. 1990; Master 1991; Lunney et al. 1996; IUCN 2001). For example, the International Union for the Conservation ofNature (IUCN 2001) method uses extent and changes in the amount of habitat to determine the conservation status of species. All these applications assurne that, when a model is buHt and management plans are developed, ace urate maps of habitat area and spatial arrangement are available. Alternatively, threats to species may be evaluated and explored with population vi ability analysis (PVA, Boyce 1992; Burgman et al. 1993; Possingham et al. 1993, Chap. 6, this Vol.). A PVA will produce a probability of extinction or quasi-extinction over a specified time frame for a given management scenario, providing a direct measure of the expected success of management options for rare, threatened and sensitive species. PVAs can be made spatially explicit and can incorporate information concerning the demographie attributes of a species, habitat preferences, dispers al between habitat patches, and the occurrence of disturbances or catastrophes (Chaps. 6, 7,11, this Vol.). Data and understanding are never sufficient for precise prediction (Coulson et al. 2001), but PVAs may provide a means of synthesizing what is known, discriminating between management alternatives and establishing an ecological context for interim judgments about preferred spatial configurations of habitat. Habitat maps are a co re component of PVAs for two main reasons. Firstly, before a population model is developed,a species' spatial structure is an important consideration in deciding whether to use a single population model or a metapopulation model (Chaps. 6, 11, this Vol.). The spatial structure also proEcological Studies, Vol. 165 C.A. Brigham, M.W. Schwartz (Eds.) Population Viability in Plants © Springer-Verlag Berlin Heidelberg 2003
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J. Elith and M.A. Burgman
vides the basis for the design of sampling efforts to support the estimation of parameters for disturbance, dispersal, habitat loss, and fragmentation. These parameters may be built into a population model and used to represent trends in habitat quality, extent, and spatial arrangement (Chap. 11, this Vol.). Secondly, management decisions are often spatially explicit. Once the results of a PVA are available, decisions that relate to the protection or enhancement of populations or habitat can only be implemented with a reliable habitat model. These steps require a map that reflects both the current distribution of the species and the potential suitability of the landscape to maintain viable popul
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