Effective population size (N(e)) is a key parameter to understand evolutionary processes and the viability of endangered populations as it determines the rate of genetic drift and inbreeding. Low Ne can lead to inbreeding depression and reduced population adaptability. In this study, we estimated contemporary N(e) using genetic estimators (LDNE, ONeSAMP, MLNE and CoNe) as well as a demographic estimator in a natural insular house sparrow metapopulation. We investigated whether population characteristics (population size, sex ratio, immigration rate, variance in population size and population growth rate) explained variation within and among populations in the ratio of effective to census population size (N(e)/N(c)). In general, N(e)/N(c) ratios increased with immigration rates. Genetic N(e) was much larger than demographic N(e), probably due to a greater effect of immigration on genetic than demographic processes in local populations. Moreover, although estimates of genetic N(e) seemed to track N(c) quite well, the genetic N(e) -estimates were often larger than Nc within populations. Estimates of genetic N(e) for the metapopulation were however within the expected range (<N(c)). Our results suggest that in fragmented populations, even low levels of gene flow may have important consequences for the interpretation of genetic estimates of N(e). Consequently, further studies are needed to understand how N(e) estimated in local populations or the total metapopulation relates to actual rates of genetic drift and inbreeding.
Keywords: dispersal; effective population size; genetic drift; microsatellites; population size; sex ratio.
© 2014 John Wiley & Sons Ltd.