Community Organization in Fishes as Indicated by Morphological Features

Abstract

This study uses morphological data relating to many aspects of the niche to study community organization in assemblages of stream fishes from three separate drainages. Mean values for all morphological features were compared statistically for coexisting species pairs, and those features which had significantly different means were assumed to indicate ecological differentiation that exists between the species under consideration. Average niche overlap as defined by the percentage of morphological features not differing significantly between species pairs was constant for these assemblages regardless of a nearly twofold difference in number of species present. Similarly, the average Euclidean distance between the centers of morphologically defined niches for all sympatric common species was approximately the same for all three assemblages. Moreover the distribution of Euclidean distances between species was the same in all three drainages and different than a distribution that would result from a random division of resources. Together, these results indicate that consistent patterns do exist in the organization of these stream communities, and that the species currently living together are not a random assortment of species and do not randomly divide their resources. The presence of higher numbers of species in a community seems not to be accompanied by increased packing of the niches, but rather by an occupation of more total niche space by the community as a whole.