Ecological impacts of forest fragmentation in central Amazonia

Abstract

The Theory of Island Biogeography has not lived up to its initial promise of serving practical conservation biology. Recent knowledge from the Biological Dynamics of Forest Fragments Project in Manaus, Brazil, about how the tropical rainforest ecosystem is affected by landscape fragmentation suggest that much of the ecological degradation can be accounted for by the influences of edge effects and the surrounding matrix, neither of which is addressed by Island Biogeography Theory. For example, some taxonomic groups (frogs and small mammals) show an increase in species richness in forest fragments compared to their species richness before isolation. This type of result is clearly not predicted by the Theory of Island Biogeography, but can be accounted for with information on how species react to the presence of a new matrix habitat. The importance of edge effects in modifying forest dynamics (tree mortality and recruitment, biomass loss, and community composition of trees) as well as influencing species distributions, in some cases, may overwhelm the fragmentation effects related to patch size. It is becoming increasingly clear that the effects of habitat fragmentation are being driven by two main processes: the within-patch effects linked to the creation of forest edge, and the outside-patch influence of matrix habitat. The latter process includes a broader landscape-level interaction of habitat configuration (patches, matrix, connectivity). The management of landscapes should, therefore, take into account these considerations.