Proximate and ultimate drivers of variation in bite force in the insular lizards Podarcis melisellensis and Podarcis sicula

Bite force is a key performance trait in lizards since biting is involved in many ecologically relevant tasks, including foraging, fighting, and mating. Several factors have been previously suggested to impact bite force in lizards, such as head morphology (proximate factors), or diet, intraspecific competition, and habitat characteristics (ultimate factors). However, these have been generally investigated separately and mostly at the interspecific level. We tested which factors drive variation in bite force at the population level and to what extent. Our study includes 20 populations of two closely-related lacertid species, Podarcis melisellensis and Podarcis sicula, which inhabit islands in the Adriatic. We found that lizards with more forceful bites have relatively wider and taller heads, and consume more hard prey and plant material. Island isolation correlates with bite force, likely by driving the resource availability. Bite force is only poorly explained by proxies of intraspecif...