ESTIMATING THE EFFECTIVE POPULATION-SIZE OF CONSERVED POPULATIONS

Accurate estimation of effective population size is important in attem pts to conserve small populations of animals or plants. We review the genetic and ecological methods that have been used to estimate effecti ve population size in the past and suggest that, while genetic methods may often be appropriate for the estimation of N. and its monitoring ecological methods have the advantage of providing data that can help predict the effect of a changed environment on N(e). Estimation of N(e ) is particularly complex in populations with overlapping generations, and we summarize previous empirical estimates of N(e) that used ecolo gical methods in such populations. Since it is often difficult to asse ss what parameters and assumptions have been used in previous calculat ions, we suggest a method that provides a good estimate of N(e), makes clear what assumptions are involved, and yet requires a minimum of in formation. The method is used to analyze data from 14 studies. In 36% (5) of these studies, our estimate is in excellent agreement with the original, and yet we use significantly less information; in 21% (3) th e original estimate is markedly lower, in 43% (6) it is markedly highe r. Reasons for the discrepancies are suggested. Two of the underestima tes involve a failure in the original to account for a long maturation time, and four of the overestimates involve problems in the original with the correction for overlapping generations.