Evidence for ecological release over a fine spatial scale in a lizard from the White Sands formation

Abstract

When a population experiences relaxation of selective pressures due to reduced predation or competition, it may undergo ecological release. Ecological release often manifests as increased niche breadth and trait variation, as individuals have the opportunity to exploit a wider variety of resources. At the recently‐colonized White Sands dune formation in New Mexico, lizards from white sand habitat have fewer predators and competitors than their dark soil counterparts, and show evidence of ecological release compared to dark soil lizards. To determine whether the dynamics of ecological release also play out over an even finer habitat gradient, we studied southwestern fence lizards in the center of the White Sands dune formation and the narrow ecotone between White Sands and the surrounding dark soil habitats. We predicted that lizards from the central dunes would exhibit ecological release in terms of broadened resource use compared to lizards from the ecotone. We first conducted avian surveys in both the central dunes and ecotone habitats to measure abundance, richness and diversity of avian species that could act as lizard predators. Next, we measured microhabitat‐scale resource use by comparing perch selection of lizards in both habitats. Finally, we measured landscape‐scale resource use by quantifying home range sizes and daily distances traveled by lizards in both habitats. We found that central dunes lizards used a greater diversity of perch types, and had greater variation in both home range size and daily distances traveled, than ecotone lizards. There were fewer predatory bird species in the central dunes than on the ecotone, and there was a tendency for fewer predation events in the central dunes than on the ecotone. Our results demonstrate that ecological release is detectable over a fine habitat gradient, such as between the center of a recently‐colonized habitat and its ecotone with the surrounding ecosystem.