NESTED SUBSET ANALYSES OF COLONIZATION-DOMINATED COMMUNITIES - METAZOAN ECTOPARASITES OF MARINE FISHES

Communities have a nested subset structure if the species comprising d epauperate assemblages represent non-random subsets of progressively r icher communities. Nestedness results from differential extinction pro babilities, differential dispersal and colonization probabilities, nes ted environmental tolerances, or facilitated succession. Previous rese arch suggests that the frequency of significant nestedness, and the de gree of nestedness as measured by a standardized index, C, should be g reater for extinction-dominated communities than colonization-dominate d communities. To test these hypotheses, we conducted nestedness analy ses on 38 communities of metazoan gill and head ectoparasites infectin g different species of marine fishes. Extinction, environmental tolera nces and niche space, and interspecific interactions do not significan tly influence the structure of these ectoparasite communities. As such , they provide an appropriate system in which to examine the frequency and degree of nestedness in colonization-dominated assemblages relati ve to extinction-structured communities; Using two common analyses, we found that nestedness in these ectoparasite communities was rare (1 o f 38 communities after a conservative Bonferroni correction for multip le comparisons). However, the mean standardized nestedness score (C = 0.483 +/- 0.243) was not significantly different from the mean nestedn ess score of extinction-structured communities reported in the literat ure. Therefore, although these communities do seem less nested than ex tinction-dominated communities (from the frequency analysis), the C st atistic is unable to distinguish these groups. Also, neither the frequ ency of significant nestedness nor mean standardized C scores were rel ated to mean water temperature, host habitat (benthic, pelagic, or ben thopelagic), host trophic level (herbivore, planktivore, predator, or omnivore), or whether or not the host is a schooling species. These re sults confirm previous conclusions stating that these communities are largely random, unstructured assemblages.