Ecological release and directional change in White Sands lizard trophic ecomorphology

Abstract

A species’ trophic ecomorphology can change drastically following the colonization of a new environment. Resource shifts may result in dietary change of colonists and therefore, the evolution of ecomorphological adaptations such as changes in bite force, head, and body size. To understand the drivers and dynamics of ecomorphological change after colonization we studied prey availability, diet, performance, and morphology in three lizard species (Aspidoscelis inornata, Holbrookia maculata, and Sceloporus cowlesi) in the ecologically distinct environment of White Sands, New Mexico. White Sands, which formed within the last 6,000 years, was most likely colonized by nearby “dark soils” populations. Therefore, for each species we compared White Sands individuals to conspecific inhabiting the surrounding Chihuahuan Desert habitat. The White Sands habitat had higher prey morphospecies richness, increased breadth of prey orders, and a higher percentage of hard-bodied prey than the dark soils habitat. Differences in prey availability in White Sands and dark soils habitats were reflected in lizard diets. Specifically, morphospecies richness and percentage of hard bodied prey were higher in the diet of White Sands lizards compared to dark soils lizards. These similarities in resource use across the three species in two habitats indicated parallel responses to a shared environment. Although some dietary shifts in the three species were predictable and reflected prey availability, differences in performance and morphology traits indicated different ecological responses in each species. In general, average prey hardness was higher in the two White Sands species that had stronger absolute bite force and larger absolute head size. While White Sands lizards generally also included a larger proportion of hard prey in their diets, had higher absolute bite-force, head size, and body size than dark soils lizards, the magnitude of these differences varied across species.