Mechanisms that Drive Evolutionary Change INSIGHTS FROM SPECIES INTRODUCTIONS AND INVASIONS

to estimate how levels of genetic diversity in non-native populations are different from those of their source populations. While it is typically assumed that a significant loss of diversity will be associated with species introductions, the actual effect may be more complex, depending on propagule pressure and patterns of diversity and population structure in the native range of a species. We review a number of studies of animal species introductions in which allelic diversity and heterozygosity in the non-native and source ranges of each species can be compared, and find that the typical loss of diversity is minimal. The generality of this pattern may provide new insight into debates over the prevalence of stochastic processes in generating novel phenotypes or coadapted gene complexes in founder populations. These results suggest that the response of founder populations to natural selection in a novel environment is generally more important than the stochastic effects of the founder event itself in determining the evolutionary trajectory of a population. Mechanisms that Drive Evolutionary Change