Head shape predicts isotopic diet in anoles and day geckos

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,..., ,