Extinction in Nature Reserves: The Effect of Fragmentation and the Importance of Migration between Reserve Fragments

Abstract

Simulation time is crucial to how the risk of extinction changes with fragmentation. For short to moderate time spans the probability of extinction increases exponentially with the degree of fragmentation. When the time span considered is long enough relative to the size of the reserve, the relationship is sigmoidal. With increasing time span or decreasing reserve size the curve gets steeper. Eventually only the sheer incline and ensuing plateau of a truncated sigmoidal curve remains. Consistently, a species is more likely to survive in a continuous tract of natural habitat than in one that is subdivided into isolated parcels. Migration can greatly reduce the extinction probability of species in fragmented reserves. The persistent disagreement in the SLOSS debate is discussed, and an attempt is made to explain why conflicting recommendations have emerged.