Evolution and the Consequences of Species Introductions and Deletions

The addition or deletion of a species from a community is likely to have effects on the trait values of other species and on their population densities. This article argues that current theory is insufficiently developed to provide guidance in predicting what might happen to either traits or population densities. In addition, there has been relatively little empirical work to examine many of the phenomena that have been predicted by the limited available theory. The example of character displacement of competitors is reviewed to reveal some of the gaps in our knowledge about the evolutionary consequences of additions or deletions. The example of evolution of traits related to predation in food webs is used to reveal gaps in our knowledge of the population—level consequences of evolutionary changes initiated by a species addition or deletion. Several approaches to studying combined evolutionary and ecological processes in multispecies communities are discussed. Some previous multispecies models have been too abstract to be easily related to more mechanistic two—species models, but recent methods derived from quantitative genetics may result in significant advances in understanding multispecies systems and their relationship to communities with fewer species.