A simulation study on the viability of Sri Lankan elephant Elephas maximuspopulations: Retrospective model validation and future perspectives

Despite some criticism, population viability analysis (PVA) by means of est imating the risk of extinction of populations through computer simulation h as become a valuable tool in conservation and management. One point of crit icism is the potentially improper implementation of the life history parame ters of real population in the standard PVA models. Here we validate an exi sting individuum-based stochastic simulation model specifically implementin g life history features of Asian elephants Elephas maximus for a PVA of Sri Lankan populations. Using this model, a simulation of the last 2300 years yields realistic expectations for extant population size, sex ratio, and th e relative proportion of tusk-bearing males, when mean calving intervals of 4.0 to 4.1 years are implemented. The primary determinants of the long ter m population trend are female mortality and mean calving interval. For the two simulated populations at Mahaweli and Yala, the present extinction risk appears to be less than in former centuries, presumably due to the impleme ntation of conservation measures. Nevertheless, potential threats of Sri La nkan elephant populations are (1) actions which increase female and/or juve nile mortality, (2) isolation of small populations due to habitat fragmenta tion, and (3) negative trends in carrying capacity, which have been reporte d for at least one population. Due to its low maximum intrinsic growth rate , populations of Asian elephant might take a long time to recover, even if a threat is removed.