Head shape predicts isotopic diet in anoles and day geckos

Abstract

Abstract Trophic morphology affects resource acquisition; therefore, species differences in such traits may be informative for inferring resource use overlap and potential species interactions. In lizards, head size and shape determine the size and hardness of prey that can be consumed. Lizards with large differences in head morphology are expected to overlap less in prey use than lizards with more similar traits. Stable isotopes are increasingly being used to describe diet, yet how traditional functional traits affect isotopic diet is often not clear a priori. We measured head size, head shape, 𝛿15N, and 𝛿13C under controlled resource availability in an enclosure experiment using introduced lizards in Hawaiʻi to test whether functional traits predict isotopic diet. Brown anoles Anolis sagrei had the tallest and narrowest heads, the highest values of 𝛿13C, and the lowest values of 𝛿15N. Gold dust day geckos Phelsuma laticauda had the shortest and widest heads, the lowest values of 𝛿13C, and the highest values of 𝛿15N. Green anoles Anolis carolinensis were intermediate in both diet and morphology. As a result of isotopic diet overlap, green anoles have reduced competitor‐free resource space in the presence of both of the other lizard species. Head shape was the best predictor of diet and the only trait that explained variation within as well as among species. Head size was sexually dimorphic, and therefore the weaker diet correlations with this trait may be explained by sexual selection. Breadth in morphospace did not correlate with isotopic diet breadth, nor did the amount of overlap in morphospace predict the amount of overlap in isotopic diet space. While lizards were able to locally depress prey in experimental enclosures, no shifts in diet were detected in response to the presence of heterospecifics. The generality of head shape in predicting isotopic diet, and whether it does so independent of habitat use, warrants additional study. Head shape provides a potentially fruitful avenue for trait‐based approaches to studying ecology and evolution in lizards. Read the free Plain Language Summary for this article on the Journal blog.