Ecological release occurs at multiple spatial scales in a lizard from New Mexico's White Sands formation

Background/Question/Methods

When a population experiences a relaxation of selective pressures due to reduced predation or competition, it may undergo ecological release.  Ecological release often results in broader niches or increased trait variation as individuals have the opportunity to exploit a wider variety of resources.  We compared predator and competitor abundance, and resource use at the microhabitat and landscape scales, in the Eastern Fence Lizard, Sceloporus cowlesi, at White Sands, New Mexico. We compared lizards from the heart of the White Sands dunes to lizards from the ecotonal transition zone between white sand and dark soil habitats. Our prediction was that the white sand habitat would have fewer predators and competitors than the ecotone, and therefore lizards there would show evidence of ecological release in terms of broadened resource use.  We conducted transect surveys to quantify predator and competitor abundance in both habitats.  We measured microhabitat resource use by comparing the type and characteristics of perches selected by lizards in both habitats.  Finally, we measured landscape-scale resource use by quantifying home range sizes and daily distances moved by lizards in both habitats using radio-telemetry. 

Results/Conclusions

We observed fewer predators and competitors in the white sand habitat than in the ecotone habitat.  Additionally, we found that lizards in the white sand habitat used a greater diversity of perch types at the microhabitat scale, and had greater variation in both home range size and daily distances moved at the landscape scale, than ecotonal lizards.  Our results provide evidence consistent with ecological release having occurred in the white sand habitat, and support the hypothesis that populations undergoing ecological release will demonstrate broadened resource use at multiple spatial scales.