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Gap analysis is an approach to conserving biological diversity that maps species richness and identifies sites that ought to be protected but are not in conservation networks. Gap analyses based on species richness may have high error rates when species models are based solely on species-habitat association, because patches too small to support populations are still considered to be potential habitat. We incorporated information on the home range and dispersal distances of the mammals of Florida to estimate minimum critical areas (MCA) to support minimum viable populations for each mammal species. Incorporating MCA decreases the area occupied by the highest levels of species richness and alters the mapped spacial distribution of potential species richness. For example, in St. Lucie and Okeechobee counties, Florida, the total area occupied by 15 or more species was 30,448 ha under simple mammal-habitat association models, but only 7820 ha under model conditions incorporating MCA. This reflects the fragmented condition of many landscapes, where most patches are too small to support viable populations of larger species. Incorporating minimum area requirements into maps of potential species richness produces more conservative and defensible maps.