Mechanistic Approach to the Structure of Animal Communities:AnolisLizards and Birds

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The role of competition in structuring animal communities is currently hotly debated. One of the crucial assumptions underlying the concept of resource partitioning as a function of competition is the jack-of-all-trades, master of none principle: differences in morphology and behavior results in the different abilities to use different resources and hence results in the potential to partition those resources. Examination of the manner by which habitat structure constrains resource use offers a mechanistic approach to study community structure. Anolis lizards provide a useful example to illustrate the approach since in the West Indies they show consistent assemblages of ecomorphs from island to island. The bases for a strong influence of habitat structure on the resource use pattern of anoles are reviewed as a preamble to a new analysis of the 2-species Anolis assemblages in the Lesser Antilles. The two species on the island of Grenada show a strong morphological segregation associated with different use patterns of similar microhabitats. The two species on St. Kitts in a richer habitat show strong microhabitat segregation but little morphological difference apart from size. A related pair of species on Antigua in a habitat similar to that on Grenada appear to be constrained in the degree of habitat segregation and, perhaps as a consequence, show morphological segregation similar to that documented for the species on Grenada. These comparisons provide further evidence of the strong influence of habitat structure on the morphology and habitat partitioning patterns of coexisting species. Field and experimental studies of coexisting bird assemblages suggest that details of habitat structure also have a strong influence on their morphology and resource use patterns. Studies focusing on the manner by which animals use different microhabitats provide a useful, mechanistic approach to study the influence of competition on community structure