Dynamic biogeography and conservation of endangered species

As one moves from the core to the periphery of a species' geographical rang e, populations occupy less favourable habitats and exhibit lower and more v ariable densities(1-4). Populations along the periphery of the range tend t o be more fragmented and, as a result, are less likely to receive immigrant s from other populations. A population's probability of extinction is direc tly correlated with its variability and inversely correlated with density a nd immigration rate(5-9). This has led to the prediction that, when a speci es becomes endangered, its geographical range should contract inwards, with the core populations persisting until the final stages of decline(2,10). C onvinced by these logical but untested deductions, conservation biologists and wildlife managers have been instructed to avoid the range periphery whe n planning conservation strategies or allocating resources for endangered s pecies(11-13). We have analysed range contraction in 245 species from a bro ad range of taxonomic groups and geographical regions, Here we report that observed patterns of range contraction do not support the above predictions and that most species examined persist in the periphery of their historica l geographical ranges.