Time frames for population viability analysis of species with long generations: an example with Asian elephants

We extend an earlier population viability analysis (PVA) of the Asian elephant (Elephas maximus) conducted by Sukumar & Santiapillai (1993) in order to examine how conclusions about viability can depend upon the time frame examined. We find that there is an approximately 200 year lag period before extinction events begin to occur in slowly declining populations of E. maximus. Therefore, examining population persistence over a 100 year time frame seriously underestimates the risk of population extinction over a longer, 1000 year period. These results are supported by the use of both a species-specific model of elephant demography, ELEPHANT, and a generic PVA package, VORTEX. For populations with long generations, a 100 year time period will often not be sufficient to evaluate demographic processes leading to extinction. These results have important implications for how investigators conduct PVAs, and for the listing of endangered species by the World Conservation Union (IUCN).