An early synthesis of the habitat amount hypothesis

Abstract

The ecological literature is filled with studies highlighting the importance of both habitat loss and fragmentation on biodiversity. The patch concept has been central to these findings, being also at the heart of many ecological theories. Recently, the habitat amount hypothesis has been proposed as an alternative, where the patch concept is put to a rest, and both patch size and patch isolation effects on species richness are reduced to a single gradient: habitat loss in the landscape. As this theory stated clear predictions that could be experimentally tested, many formal tests of the hypothesis have been published recently and this study aims at synthesizing their results. A meta-analysis of 13 tests of the habitat amount hypothesis was conducted, to produce a single combined test of the theory. The 13 tests combined suggest that effects of patch size and isolation, while controlling for habitat amounts, do exist although their overall effect is weak (r = 0.158). Literal interpretations of the habitat amount hypothesis, where patch size and isolation have absolutely no effect on species richness, are probably oversimplifications of the processes at work. Still, the theory could prove useful as a baseline of the effects of habitat loss, against which patch size and isolation effects must be contrasted.