Identification of selective sources: partitioning selection based on interactions.

Interspecific interactions are an inescapable reality in nature. The evolution of a species is largely determined by the environment, abiotic or biotic, in which selection occurs. Quantifying the magnitude of selection is crucial to understanding which aspects of the environment are important to the evolution of a species. Such knowledge is particularly important to fields such as conservation biology, which attempts to maintain a suitable environment for the prosperity of a species, or coevolution, where dynamics are determined by the strength of reciprocal selection between species. I present a general method by which selection due to interspecific interactions may be quantified. This technique is based on past quantitative genetic models of selection and can be used with other methodologies that build on these standard models. The approach may be expanded to account for n-species interactions (e.g., a plant with two pollinators). Simulation studies conducted using this method indicate that the magnitude of selection between two species is strongly correlated with the presence of nonrandom interactions.