NATURAL DIE-OFFS OF LARGE MAMMALS - IMPLICATIONS FOR CONSERVATION

The viability of populations is a central concern of biological conser vation The occurrence of catastrophic die-offs may greatly reduce the long-term viability of populations. Theoretical extinction models and viability analyses require information on the frequency of die-offs an d on the distribution of die-off severities. A review of literature id entified 96 natural die-offs in large mammal populations, with a die-o ff being defined as a peak-to-trough decline in estimated population n umbers of at least 25%. If such die-offs are common, population viabil ity analyses that ignore them may be overly optimistic. The severities of the natural die-offs of large mammals presented here are not unifo rmly distributed There is a relative overabundance of die-offs in the 70-90% range, and an underabundance of die-offs greater than 90%. This may indicate the presence of buffers against population extinction. T he reported causes of large mammal die-offs were significantly related to trophic level: herbivore die-offs were more often attributed to st arvation, while carnivore die-offs were more often attributed to disea se. Populations subject to large-scale phenomena such as drought and s evere winters may not be protected from die-offs by population subdivi sion. On the other hand, populations subject to catastrophic disease e pidemics may be protected by subdivision, and threatened by corridors between conservation areas and by translocation efforts.