Population genomics has the potential to improve studies of evolutionary genetics, molecular ecology and conservation biology, by facilitating the identification of adaptive molecular variation and by improving the estimation of important parameters such as population size, migration rates and phylogenetic relationships. There has been much excitement in the recent literature about the identification of adaptive molecular variation using the population-genomic approach. However, the most useful contribution of the genomics model to population genetics will be improving inferences about population demography and evolutionary history.

Population census size (N C ) and effective population sizes (N e ) are two crucial parameters that influence population viability, wildlife management decisions, and conservation planning. Genetic estimators of both N C and N e are increasingly widely used because molecular markers are increasingly available, statistical methods are improving rapidly, and genetic estimators complement or improve upon traditional demographic estimators. We review the kinds and applications of estimators of both N C and N e , and the often undervalued and misunderstood ratio of effective-to-census size (N e /N C ). We focus on recently improved and well evaluated methods that are most likely to facilitate conservation. Finally, we outline areas of future research to improve N e and N C estimation in wild populations.

International audienceA series of important new theoretical, experimental and observational studies demonstrate that just a few immigrants can have positive immediate impacts on the evolutionary trajectory of local populations. In many cases, a low level of immigration into small populations has produced fitness benefits that are greater than those predicted by theoretical models, resulting in what has been termed 'genetic rescue'. However, the opposite result (reduced fitness) can also be associated with immigration of genetically divergent individuals. Central to our understanding of genetic rescue are complex interactions among fundamental concepts in evolutionary and population biology, including both genetic and non-genetic (environmental, behavioral and demographic) factors. Developing testable models to predict when genetic rescue is likely to occur is a daunting challenge that will require carefully controlled, multigeneration experiments as well as creative use of information from natural 'experiments'