The matrix matters: Effective isolation in fragmented landscapes

As the human population expands, landscapes worldwide are becoming fragmented into remnant patches of original habitat, surrounded by agriculture and other human land uses. With diminishing opportunities to preserve large tracts of pristine habitat, the future of biodiversity conservation lies increasingly in these fragmented areas. Therefore, understanding the processes at work in fragmented landscapes has become one of the most important goals of conservation biology. Research in fragmented landscapes has traditionally focused on the remnant patches themselves and their simple geometry within the landscape (e.g., patch quality, patch size and shape, inter-patch distance, corridors of native habitat). Habitat fragments are thus considered to be analogous to islands in a surrounding sea of non-habitat, referred to as the “matrix.” Both theoretical and empirical studies of fragmented areas most often assume the matrix to be uniform, measuring isolation among patches simply as the distances separating them. Terrestrial habitat fragments, however, are usually surrounded by a complex mosaic of other land cover types, which may be differentially permeable to individuals moving among the fragments. Therefore, patches may be more or less effectively isolated than simple distance would indicate (and classic models would predict), depending on the type of intervening matrix. It’s astonishing to discover how often a seemingly novel idea in ecology actually was proposed by Darwin 140