THE PARASITES OF ANOLIS LIZARDS THE NORTHERN LESSER ANTILLES .2. THE STRUCTURE OF THE PARASITE COMMUNITY

The communities of parasitic helminths from ten species of lizards on seven islands in the Caribbean were examined to ascertain the relative importance of predictable deterministic factors and unpredictable colonization or extinction events in determining the structure of the parasite community. A simple graphical model of community structure is used as a "null model" to describe the features of a community that are dependent only upon the size of the host population and features of the life histories of the constituent parasite species. This model predicts that parasite species will exhibit a nested pattern of local and global relative abundance. The observed data correspond fairly well to this pattern. The absences of individual parasite species from communities where they might be expected to be present emphasizes the role of stochastic colonization and extinction events in delineating the constituent members of the community on any island. Statistical analysis of the distribution of parasite species per host illustrates that this pattern is random in habitats where parasite species diversity is low, but decreasingly variable in habitats where more diverse parasite communities occur. Increased parasite diversity also leads to an increase in the proportion of hosts that contain mixed species infections. Comparisons of worm burdens from single and mixed species infections within individual hosts suggest that interactions between parasite species only rarely leads to reduced worm burdens.