Habitat fragmentation and biodiversity collapse in neutral communities

Models of habitat fragmentation have mainly explored the effects on a few-species ecologies or on a hierarchical community of competitors. These models reveal that, under different conditions, ecosystem response can involve sharp changes when some given thresholds are reached. However, perturbations, recruitment limitation and other causes may prevent competitive hierarchies from actually operating in natural conditions: the process of competitive exclusion underlying hierarchies could not be a determinant factor structuring communities. Here we explore both spatially-implicit and spatially-explicit metapopulation models for a competitive community, where the colonization-extinction dynamics takes place through neutral interactions. Here species interactions are not hierarchical at all but are somehow ecologically equivalent and just compete for space and resources through recruitment limitation. Our analysis shows the existence of a common destruction threshold for all species: whenever habitat loss reaches certain value a sudden biodiversity collapse takes place. Furthermore, the model is able to reproduce species-rank distributions and its spatially explicit counterpart predicts also species-area laws obtained from recent studies on rainforest plots. It is also discussed the relevance of percolation thresholds in limiting diversity once the landscape is broken into many patches. (c) 2004 Elsevier B.V. All rights reserved.