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Evolutionary Ecology Research




Evolutionary Ecology

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Since flight imposes physical constraints on the attributes of a flying organism, it is expected that the distribution of body sizes within clades of small-bodied flying vertebrates should share a similar pattern that reflects these constraints. We examined patterns in similarities of body mass distributions among five clades of small-bodied endothermic vertebrates (Passeriformes, Apodiformes + Trochiliformes, Chiroptera, Insectivora, Rodentia) to examine the extent to which these distributions are congruent among the clades that fly as opposed to those that do not fly. The body mass distributions of three clades of small-bodied flying vertebrates show significant divergence from the distributions of their sister clades. We examined two alternative hypotheses for similarities among the size frequency distributions of the five clades. The hypothesis of functional symmetry corresponds to patterns of similarity expected if body mass distributions of flying clades are constrained by similar or identical functional limitations. The hypothesis of phylogenetic symmetry corresponds to patterns of similarity expected if body mass distributions reflect phylogenetic relationships among clades. Empirically, the clades with the most similar body mass distributions are the Passeriformes and Chiroptera, a result inconsistent with similarities among distributions being attributable to phylogeny. However, the other clade of flying species (Apodiformes + Trochiliformes) was less similar to either Passeriformes or Chiroptera than was the Insectivora, which is inconsistent with the pattern expected if body size distributions were influenced by constraints of flight. A test for phylogenetic symmetry indicated that the empirical pattern of similarity was statistically inconsistent with this hypothesis, while a test for functional symmetry indicated that the empirical pattern was statistically consistent with this hypothesis, though not perfectly congruent. Hence, we conclude that there is evidence that functional constraints influence similarities in body mass distributions among species of distantly related taxa.

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