CAN ECOLOGICAL THEORY PREDICT THE DISTRIBUTION OF FORAGING ANIMALS - A CRITICAL ANALYSIS OF EXPERIMENTS ON THE IDEAL FREE DISTRIBUTION

Opinions differ on the empirical success of the Ideal Free Distribution. The Ideal Free model predicts that the distribution of organisms between resource sites should match the distribution of resources. Many studies report support for this prediction. We review tests of this model utilising a method of analysis derived from the psychological principle called the matching law. Our reanalysis revealed that the distribution of organisms is consistently less extreme than the distribution of resources. This systematic deviation from the Ideal Free Distribution means organisms underuse richer sites and overuse poorer sites. We examine how deviations from the Ideal Free Distribution may arise as a consequence of discrimination constraints, competitive interactions, competitive asymmetries and travel between sites, and recommend ways in which the design of future tests of the Ideal Free Distribution may be improved.