Effective Population-Size And Lifetime Reproductive Success

The mean and variance of lifetime reproductive success, E(LRS) and V-LRS, influence the ratio of effective to census population size, N-e/N-c. Because the complete data needed to calculate E(LRS) and V-LRS are seldom available, we provide alternatives for estimating N-e/N-c from incomplete data. These estimates should be useful to conservation biologists trying to compute the effective size of a censused population. An analytical approach makes assumptions regarding the process influencing offspring survival. We provide a method for examining the validity of those assumptions and show that particular violations can result in either over or underestimates. When the assumptions are violated or when more data are available, we suggest estimating N-e/N-c using computer stimulations of models based on individuals. We examine how such simulations can be used to estimate N-e/N-c using an individual-based model for Lesser Snow Geese (Anser caerulescens). We demonstrate that such estimates can be biased unless the simulations are based on complete cohorts and samples of known age. We show that because the estimate of N-e/N-c depends on the stage of the reproductive cycle used as a point of reference in the model, the census population size N-c must be based on the same stage to provide unbiased estimates of N-e.