Morphologically Inferred Niche Differentiation in Stream Fishes

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Abstract
General statements about the ecological significance of morphological features in freshwater fish were used to predict differences in resource use among 10 pairs [including Nocomis leptocephalus, Semotilus atromaculatus, Notropis chiliticus, N. analostanus, N. altipinnis, N. alborus, N. ardens, Clinostomus funduloides, Lepomis gulosus, L. cyanellus, Esox niger, E. americanus, Lepomis auritus, L. gibbosus and Phoxinus oreas] of similar sympatric species. Results of gut content analyses supported inferred differences between species in prey size and type or in foraging site in 90% of the cases. Inferred differences between species in habitat were supported by collection records and/or field observations in all cases except for 2 pairs in which no differences in resource use were identified. The use of morphological inference to identify ecological differences between quite similar species pairs works for freshwater fish. All 10 spp. pairs discussed showed differences in morphology related to both the habitat and food dimensions; and, for all species combined, differences in these 2 major dimensions occurred with equal relative frequency. This last result contrasts with theoretical predictions for competitively structured communities (i.e., niche compression hypothesis) but agrees with some earlier empirical results for aquatic animals.