Morphological evolution of birds recently introduced to islands: Patterns of diversification

Evolution was originally considered to be observable only over geological time scales. It has recently become apparent that evolutionary changes can be detected over contemporary time periods. Exotic species often experience intense selection, making them good model systems for investigating evolutionary changes over contemporary time. We often know details of the introductions, such as exact time, location of the source population, founding propagule size, and establishment history. These details allow us to formulate hypotheses concerning the evolutionary changes expected in these species' exotic ranges.;I examined contemporary morphological evolution of passerine birds introduced to islands. Passerine birds have been introduced to many islands world-wide, making them conducive for examining patterns of insular evolution. In chapters one and two, I evaluated whether these species conform to the Island Rule, an ecogeographic rule based on the study of native insular species. It states that, on islands, small species should increase in body size while large species should decrease body size. All of the species I studied are small, therefore they were expected to increase in body size. I found equivocal results concerning the Island Rule. In chapter one, I found that the great kiskadee (Pitangus sulphuratus) follows the Island Rule, as it is larger in its exotic island range than in the native source range. However, in chapter two, I found no clear Island Rule pattern examining 39 insular populations. However, I did find a clear pattern of decrease in wing length and increase in tail length. Although these populations may not be following an overall Island Rule pattern, they are still adapting to their exotic environments. In chapter three, I evaluated among-island diversification of six passerine species introduced to the Hawaiian archipelago. Five of these six species show some morphological differentiation between islands, and at least some of this differentiation cannot be accounted for by genetic drift.;The results of this dissertation provide further support for the idea that evolutionary divergence can happen over contemporary time scales. The passerine bird populations examined in these chapters have adapted to local conditions, giving us insights into the genesis of evolutionary diversity.