Mechanistic Approach to the Structure of Animal Communities: Anolis Lizards and Birds

The role of competition in structuring animal communities iscurrently hotly debated. One of the crucial assumptions underlyingthe concept of resource partitioning as a function of competitionis the jack-of-all-trades, master of none principle: differencesin morphology and behavior results in the different abilitiesto use different resources and hence results in the potentialto partition those resources. Examination of the manner by whichhabitat structure constrains resource use offers a mechanisticapproach to study community structure. Anolis lizards providea useful example to illustrate the approach since in the WestIndies they show consistent assemblages of ecomorphs from islandto island. The bases for a strong influence of habitat structureon the resource use pattern of anoles are reviewed as a preambleto a new analysis of the 2-species Anolis assemblages in theLesser Antilles. The two species on the island of Grenada showa strong morphological segregation associated with differentuse patterns of similar microhabitats. The two species on St.Kitts in a richer habitat show strong microhabitat segregationbut little morphological difference apart from size. A relatedpair of species on Antigua in a habitat similar to that on Grenadaappear to be constrained in the degree of habitat segregationand, perhaps as a consequence, show morphological segregationsimilar to that documented for the species on Grenada. Thesecomparisons provide further evidence of the strong influenceof habitat structure on the morphology and habitat partitioningpatterns of coexisting species. Field and experimental studiesof coexisting bird assemblages suggest that details of habitatstructure also have a strong influence on their morphology andresource use patterns. Studies focusing on the manner by whichanimals use different microhabitats provide a useful, mechanisticapproach to study the influence of competition on communitystructure