Endangered Species Constrained by Natural and Human Factors: the Case of Brown Bears in Northern Spain
We developed a conceptual framework for classifying habitat quality that requires the construction of separate habitat models for each key demographic feature; the framework can be applied when the factors that determine different demographic processes differ substantially. For example, survival of large carnivores is mainly determined by human-induced mortality, whereas nutritional condition determines reproductive rate. Hence, a two-dimensional habitat model built for reproduction and survival yields five hypothetical habitat categories: matrix, with no reproduction and/or very high mortality; sink, with low reproduction and high mortality; refuge, with low reproduction and low mortality; attractive sink, with high reproduction and high mortality; and source, with high reproduction and low mortality. We applied this framework to two endangered brown bear ( Ursus arctos ) populations in the Cantabrian Mountains, Spain. Our aim was to generate working hypotheses about the quality and spatial arrangement of bear habitat to analyze the present conditions of the different population nuclei and to facilitate identification of core areas of high conservation value, conflictive areas, or areas with unoccupied potential habitat. We used a geographic information system and two spatial long-term data sets on presence and reproduction and performed logistic regressions for building a two-dimensional model. The analysis reveals that both populations exist under different suboptimal conditions: the eastern population mainly occupies areas of suboptimal natural habitat and relatively low human impact, whereas the western population is located mainly in areas with high human impact but otherwise good natural quality. To test hypotheses about demographic features of the obtained habitat categories, we classified data on historic extinction in northern Spain ( fourteenth to nineteenth centuries ) with the two-dimensional model. Extinction probabilities within each habitat category confirmed the hypotheses: most extinctions occurred in matrix habitat, and the fewest occurred in source habitat.
Document Type: Research Article
Affiliations: 1: Department of Applied Biology, Estación Biológica de Doñana, Consejo Superior de Investigaciones Científicas, CSIC, Avda. María Luisa s/n, Pabellón del Peru, E-41013 Seville, Spain 2: Department of Ecological Modelling, UFZ-Centre for Environmental Research, Permoserstrasse 15, D-04318 Leipzig, Germany
Publication date: October 1, 2003