EFFECTS OF INDIVIDUAL HETEROGENEITY IN ESTIMATING THE PERSISTENCE OF SMALL POPULATIONS

Population viability models are commonly used to estimate the probability of pprsistence of smrll, thrcatened, or endangered populations. Demographic, temporal, spatial, and individual heterogeneity are inlportant factors affecting the probability of persistence of small populations. Bccausc stochvstic process are intractable analytically (Ludwig [lSSG]), computer simulation models are often used for estimating population viability via numerical techniques. Although demographic, spatial, and temporal stochast~city have becrl i~icurpulaLcld ir~tu some populat io~~ viability models, individual heterogeneity has not been included. In this pnpw we include individual heterogeneity in a simulation model and examine probabilities of population persistence a t different levels of heterogeneity and population size. Individual heterogencity may incrceae the probability of pelsisleoce of rrrlall populations. The mechanism for the extension in persistence may be explained by natural selection. Genotypes persisting through a decline may be those that survive better under the conditiurla cauhing tlic decline. These individuals that survive and reproduce in the face of adverse conditions may extend the probability ths t a small popnlat,ion persists. I \ 1 ,)11..1I. I , , \ . I l ' l i i l l . . \ 1 11111\1 11111 . . . . . 2 . . . . , . 1 .; .I , I , I . .I,,.., I . . ,,.1..,1."' 1. I . . : ,,I. I , . . I , . . . I t ~ ~ r . ~ . ~ t . i~.c, . ,! . 1 t,; , . I : I . > . ~