Importance of matrix habitats in maintaining biological diversity.

T he theory of island biogeography has been the central tenet of conservation biology for several decades, a tenet in which continental landscapes are viewed islands of suitable habitat patches embedded in a matrix (i.e., surrounded by a sea) of unsuitable habitat. Patch size and isolation are predicted to be the critical variables in determining the efficacy of these habitat patches in preserving biological diversity, but this paradigm has never been broadly evaluated. In a recent issue of PNAS, Prugh et al. (1) analyze a large body of available data and make the unexpected discovery that the patch size and isolation are poor predictors of patch occupancy for the majority of species reviewed. This is an important result given the centrality of the patch size-isolation tenet to much of academic conservation biology and its wide application in conservation planning and resource management. In fact, the findings of Prugh et al. (1) are largely congruent with other analyses, such as the extensive assessment of fragmentation experiments by Debinski and Holt (2). Collectively these analyses raise significant questions about the merits of island biogeographic theory as a basis for conservation biology.