EVOLUTION AND THE CONSEQUENCES OF SPECIES INTRODUCTIONS AND DELETIONS

The addition or deletion of a species from a community is likely to ha ve effects on the trait values of other species and on their populatio n densities. This article argues that current theory is insufficiently developed to provide guidance in predicting what might happen to eith er traits or population densities. In addition, there has been relativ ely little empirical work to examine many of the phenomena that have b een predicted by the limited available theory. The example of characte r displacement of competitors is reviewed to reveal some of the gaps i n our knowledge about the evolutionary consequences of additions or de letions. The example of evolution of traits related to predation in fo od webs is used to reveal gaps in our knowledge of the population-leve l 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 relat ed to more mechanistic two-species models, but recent methods derived from quantitative genetics may result in significant advances in under standing multispecies systems and their relationship to communities wi th fewer species.