Effects of insularity on genetic diversity within and among natural populations

We conducted a review of genetic diversity (GD) within and among populations in relation to categorical population size and isolation (together "insularity"). Using populations from within the same studies, we were able to control for between-study variation in methodology, as well as demographic and life histories. Contradictory to typical expectations, insularity had relatively minor effects on GD within and among population, which points to the more important roles of other factors in shaping evolutionary processes. Such effects of insularity were sometimes seen – particularly in systems (i.e. studies) where GD was already high overall. That is, insularity influenced GD in a study system when GD was high even in non-insular populations of the same system – suggesting an important role for the "scope" of influences on GD. These conclusions were more robust for within - population GD than among - population GD, although a number of biases might underlie this difference. Overall, our findings indicate that population-level genetic assumptions need to be tested rather than assumed in nature, particularly for topics highly relevant to current conservation management practices.