Effects of population characteristics and structure on estimates of effective population size in a house sparrow...

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 (