Resource use of five sympatric turtle species: effects of competition, phylogeny, and morphology

Abstract

I quantified resource use with respect to habitat, diet, and diel and seasonal use of basking time for five sympatric turtle species in a cove on Kentucky Lake, an impoundment of the lower Tennessee River in western Kentucky, U.S.A. I used pseudocommunity analyses to test for significant structure in resource use, compared resource-use matrices with matrices representing phylogenetic similarity, and measured morphological characteristics related to resource use. Three strictly riverine species (Graptemys pseudogeographica, Graptemys ouachitensis, and Apalone mutica) with relatively long limbs and digits used outer portions of the cove near deeper waters to a greater extent than did two shorter-limbed species (Trachemys scripta and Pseudemys concinna), which inhabit both lotic and lentic waters. Only the difference in habitat between A. mutica and the other four species was shown to be significant in pseudocommunity analysis, a result that can be better explained by differences in basking substrates than by competition. Dietary studies indicated two guilds, omnivore and algivore, in spite of the low pairwise overlap values that resulted from overall prey diversity. Analysis of use of diel and seasonal basking time revealed significant structure (partitioning) at only the rank of second-nearest neighbor for seasonal time. Clustering phenograms for resource similarity among the five species were overall highly similar to two phylogenetic hypotheses. Phylogeny was thus shown to be of greater importance in structuring resource use in Kentucky Lake than interspecific competition. In addition, the similarity in clustering phenograms was not consistent with the hypothesis of niche complementarity, suggesting that interspecific competition was of little importance.