KIRK O . WINEMILLER Ecological Divergence and Convergence in Freshwater Fishes

IOLOGISTS AND POUCYMAKERS ARE RAONG the clock to document and preserve biological diversity in the face of a growing global human population and alterations of natural habitats. Given the magnitude and rapid pace of changes to natural ecosys, biologists are challenged with the taSk of identifying essential features in the organization of biological communities. Notwithstanding the inherent uniqueness of different geographical regions and the evolutionary histories of their flora and fauna, the recognition of common features among communities and the species that comprise them is sometimes possible. This study contributes to our understanding of biodiversity by further examining the ecological characteristics of natural freshwater fish communities from around the world. One of ecology's greatest challenges is to explain patterns of regional species diversity as well as the ecological, morphological, and behavioral variation among and within populations. Patterns of ecological and morphological diversification are of interest to both ecologists and phylogenetic systematists. Systematists use interspecific variation as the raw material for constructing phylogenies. Ecologists would like to know if interspecific variation in a given trait arises randomly during evolutionary divergence following speciation, or whether this variation is correlated with ecological function. This difficult task is further complicated by unique events. Traits adaptive in a particular ecosystem may be neutral or maladaptive in a new environment. If a maladaptive trait is genetically correlated with one or more strongly adaptive traits, then it might persist in the population for many generations. In one form or another, evolutionary biologists and ecologists seek to identify, interpret, and model patterns of functional (adaptive) variation.21 Similarities in patterns of individual, population, and community-level variation among different faunas provide evidence that, in many cases, the same deterministic processes organize biological systems. Biological convergence is the independent evolution of the same feature (physiological, morphological, ecological, etc.) within two divergent phylogenetic lineages. Divergence is the evolution of dissimilar traits between closely related lineages. Remarkable examples of morphological and ecological divergence are well-known in vinually all higher taxa. Examples from the independent adaptive radiation among marsupial mammals of Australia and eutherian mammals of the other continents appear in most introductory biology textbooks. Convergence of ecological niches is seen in rodents and marsupial mice; shrews and marsupial insectivores; and eutherian canines and marsupial wolves. The bony fishes Figure 1. The body shape. posidon of fins. and nwuth structure of afish influence its ecological performance. Trout possess a generalited nwrphology that allows them to use the endre water column and a wide variety of food items in habitats that contain reladvely few compedng species.