VVF: integrating modelling and GIS in a software tool for habitat suitability assessment
Introduction
Habitat loss, fragmentation and alteration due to pollution, change in land use and the introduction of invasive pests are seriously threatening the health and integrity of our fauna. In conjunction with excessive hunting and poaching, they are responsible in many places for the extinction or decline of several species (Dobson, 1995). Therefore, it is increasingly important to understand the habitat requirements of endangered species, delineate the remaining suitable habitat, and effectively manage these units of habitat for the species' survival (Duncan et al., 1995). Unfortunately, even though extinction processes are widely known, wildlife conservation policies in land planning and management practice have been rarely based on formalised and transparent considerations. However, habitat-based modelling techniques that can identify remaining potential habitat and predict spatial habitat suitability are now available (Morrison et al., 1992). They facilitate the use of standard procedures that are based on quantitative methods, are clearly stated and can be repeated.
A straightforward approach to modelling wildlife–habitat relationship is the use of Habitat Suitability (HS) models. These models assess the suitability of an area for the species of interest as a function of different environmental factors (such as terrain morphology, land use, vegetation cover, meteorological conditions and distribution of human activities) which most affect species presence, abundance and distribution (Morrison et al., 1992). The resulting habitat suitability value is usually expressed as either presence–absence of animals or species potential density or probability of species occurrence. The result of this analysis is a habitat suitability map that displays the potential geographic distribution of a species in a territory (Spagnesi and Toso, 1990, Buckland and Elston, 1993). Recent developments of wildlife management planning endeavour to integrate wildlife–habitat relationship models with Geographic Information Systems (GIS) incorporating relevant habitat characteristics (Laymon and Barrett, 1994). GIS are emerging as a new tool to assist in the resolution of land use conflict and the management of natural resources (Brown et al., 1994). In particular, GIS are playing an increasingly important role in conservation biology and wildlife management because they provide an efficient means for modelling potential distribution of species and habitats (Stoms et al., 1992). GIS are very useful tools in HS maps production: they can store maps that describe environmental variables, process these geographical data through spatial analysis, create and display new HS maps (Ormsby and Lunetta, 1987, Agee et al., 1989, Roseberry et al., 1994).
Until now, most attempts for integrating GIS into HS procedures were related to a single specific case, namely a restricted area and a particular species, and could not easily be applied or extended to wider or different areas (two partial exceptions are represented by the computer program created by Ferrier, 1991, and the software HAMS developed by Roseberry and Hao, 1996). Therefore, there was a need to create a software tool capable of linking GIS with HS models so as to develop a widely applicable database management system. To this purpose we have created a program that allows a user:
—to create, modify and store new Habitat Suitability models for different species;
—to manage and store geographical data (maps) of one or more territories;
—to create Habitat Suitability maps by running HS models for a specific area.
The paper is organised as follows. First, we briefly introduce HS models, and outline pros and cons of different approaches in habitat suitability assessment. Then, we illustrate the design and development of VVF and point out the features that make this software tool very user-friendly and highly flexible. An application of the program to Ibex (Capra ibex) in an alpine area of northern Italy (Adamello Natural Park) is provided. Finally, we illustrate the role that VVF and similar software tools can play in evaluating policies and plans for wildlife management, reserve design, habitat protection and, more generally, land planning.
Section snippets
Habitat Suitability models
Fundamental elements of every HS model are the environmental variables (independent variables), the resulting habitat suitability values (dependent variables) and the classification function that links the two (Pedrotti and Preatoni, 1995) (Fig. 1). These functions commonly scale (both linearly and nonlinearly) each environmental variable between 0 and a maximum value (often 1) and then denote habitat suitability for a species as a function (more or less complicated) of these scaled values.
The design of program VVF
We developed VVF with two main characteristics in mind. First of all, VVF is very flexible. It allows for the easy modification of existing HS models, the introduction of a new HS model tuned to a specific territory and, subsequently, the recall and application of the model to a new study area with the production of a new HS map. This high degree of flexibility is guaranteed by the feature that HS models are stored separately from any maps related to their specific use for a given territory.
An example: Ibex (Capra ibex) in Adamello Natural Park
This section presents an example of application: the use of VVF to assess habitat suitability for an ungulate species (the Ibex—Capra ibex) in Adamello Natural Park. This area (481 Km2) is typical alpine habitat located in northern Italy and constitutes, together with two other Italian parks (Adamello–Brenta Regional Park and Stelvio National Park) and Switzerland's National Park, the biggest protected area in the Alps (2,500 Km2).
Ibex, once widely spread over all alpine areas in Europe, was
Conclusions
Wildlife management and conservation are problematic because of the uncertainty of populations' responses to environmental factors, human disturbance and land use changes. Therefore, any plan and policy for wildlife management and habitat protection should be based on detailed studies of ecosystems status and trends, clearly stated and repeatable. The VVF program is an innovative tool for habitat suitability assessment that satisfies this need. It integrates GIS with Habitat Suitability models,
Acknowledgements
We would like to thank Marco Ungari who helped us develop the VVF software tool. We are also grateful to the Adamello Natural Park authority, specially to Anna Bonettini and Vittorio Duccoli, for providing us with geographic and ecological data of the park area. Luca Pedrotti's suggestions during the development of this study were invaluable.
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