Evolutionary and ecological patterns of body size in North American freshwater fishes.

摘要

Although much is known about the ecology of North American freshwater fishes, few studies have incorporated phylogenetic information into analyses of ecological and biogeographic data. Consequently, little attention has been given to the relationship between evolutionary trends, and regional and local community characteristics. The objective of this dissertation is to examine evolutionary, and regional and local community patterns of body size in North American freshwater fishes, and to identify factors influencing these patterns. Cope's rule, Bergmann's rule, the energetic equivalence rule, and character displacement are examined using historical and field-collected data on North American freshwater fishes. Results from within family analyses of evolutionary trends in body size using relationships of extant species indicate that five of nine families of North American fishes contradict Cope's rule by exhibiting decreasing trends in body size as the group radiates. Results from the regional analysis of all North American fishes support Bergmann's rule by describing a negative correlation between body size and temperature. However, when within family regional patterns are examined, the trend exhibited by Salmonidae contradicts the prediction of Bergmann's rule. The energetic equivalence rule suggests that populations within a community, irrelevant of body size, use equal amounts of energy. An analysis of 30 stream fish communities sampled in Alberta, Colorado, Illinois, and Alabama indicates that stream fishes do not conform to the energetic equivalence rule. Furthermore, there is a consistent pattern of larger individuals controlling a disproportionately greater amount of resources in the stream fish communities. Finally, body size ratios of benthic riffle darters (Percidae: Etheostoma) occurring in Illinois were examined to determine if character displacement occurs among sympatric congeners. Results indicate that convergence in body size occurs in four species pairs. However, when variation in sympatric congener number is accounted for, the E. caeruleum:E. spectabile interaction results in significantly increasing size ratios (divergence) as congener number increases.