Discounting initial population sizes for prediction of extinction probabilities in patchy environments

Liu, J., 1993. Discounting initial population sizes for prediction of extinction probabilities in patchy environments. Ecol. Modelling, 70: 51-61. Extinction is a major concern in conscrvation. A most urgcnt necd is to prcdict thc rclationship of a population's initial sizc to its probability of extinction. Previous work has led to a widcly acceptcd conclusion that thc larger an initial population size. thc lcss likcly the population will go cxtinct. 1 used a spatially-explicit simulation model to investigatc extinction probabilities of Bachman's Sparrow (Airnophila aeslicw1i.c.) in patchy cnvironments. Contrary to the conventional wisdom, I found that the rclationship between extinction probabilities and initial population sizcs of thc sparrows was not correlated when initial individuals wcre in scveral patch types. To makc good prcdictions of the sparrows' extinction rates, I have suggested discounting models which incorporated initial population sizes and initial spatial distributions. The models discounted initial population sizcs on thc basis of patch characteristics (patch suitability, timing of patch suitability, and duration of patch suitability). As a result, the extinction probabilities dccreased with the logarithm of discounted population sizes. Thc discounting modcls may havc implications for quantitative predictions of cxtinction chances of other spccies, sincc most cnvironmcnts are patchy or spatially-subdivided. The discounting approach may bc also uscful for cvaluating impacts of patchy environments on population dynamics and community structure.