SPATIAL HETEROGENEITY OF LITTORAL FISH ASSEMBLAGES IN LAKES - RELATION TO SPECIES-DIVERSITY AND HABITAT STRUCTURE

We quantified the spatial heterogeneity in nearshore fish community composition within six Wisconsin lakes and examined its relation to habitat heterogeneity and species diversity. Fish abundance was estimated annually (1981-84) using seines at six sites in each lake. Substrate type, macrophyte growth form, and depth gradient were noted at each site. Species richness was estimated as the expected number of species when the number of individuals was held constant over lakes (rarefaction). Fish community spatial heterogeneity (the average percent dissimilarity in fish species composition over all possible pairs of seine sites within a lake) differed among lakes; it was positively correlated with within-lake variation in the depth gradient and with species diversity as estimated by rarefaction. We tested whether differences in community spatial heterogeneity among lakes resulted simply from differences in species diversity using a randomization test based on random permutations of the rows (seine hauls) in the species composition data matrix. Lakes differed in the extent to which the observed community heterogeneity exceeded the randomization results. Spatial heterogeneity of the fish community, as opposed to sampling phenomena resulting from differences in richness, was a strong factor in some lakes.