HIGH COMPETITION WITH LOW SIMILARITY AND LOW COMPETITION WITH HIGH SIMILARITY - EXPLOITATIVE AND APPARENT COMPETITION IN CONSUMER-RESOURCE SYSTEMS

This article investigates the relationship between the similarity of r esource capture abilities and the amount of competition between two co nsumer species that exploit common resources. Most of the analysis is based on a consumer-resource model introduced by Robert MacArthur. Con trary to many statements in the literature and in textbooks, measures of competition may decrease as similarity increases and may be greates t when similarity of the two species' sets of resource capture rates i s very low. High competition with low similarity may occur whether com petition is measured by a competition coefficient near equilibrium or is measured by the proportional increase in a species' population dens ity when its competitor is removed. However, these two measures may di ffer considerably and may change in opposite directions with a given c hange in similarity. The general conditions required for such counteri ntuitive relationships between similarity and competition are that the consumer species have relatively low resource requirements for succes sful reproduction and that the resources be self-reproducing. These sa me conditions also frequently lead to exclusion of one or more resourc es via apparent competition, and this is always true of MacArthur's mo del. A variety of other models of competition are analyzed, and circum stances most likely to produce large competitive effects with little o verlap are identified.