When populations enter novel environments, such as oceanic or habitat islands, they may escape interspecific predators and/or competitors. This ecological release can be characterized by population niche width expansion. Population niche width may expand through increased individual niche widths or, predicted by the niche variation hypothesis (NVH), greater among-individual variation. We measured population niche width and tested the NVH using the dietary niches of a community of lizards in White Sands (WS), a 650 km2 habitat island of sand dunes in New Mexico. Out of the diverse suite of squamates found in the Chihuahuan desert scrub (‘dark soils’) surrounding the dunes only three, all insectivores, have successfully invaded WS: Aspidoscelis inornata, Sceloporus cowlesi, and Holbrookia maculata. We selected 6 sites across the habitat gradient leading into WS; 2 in the dark soils, 2 on the WS / dark soils ecotone and 2 in WS. In 2015 and 2016 we measured the relative abundance and community composition of arthropods and reptiles at these sites using drift fences, funnel traps, pitfall traps and area/time constrained surveys. Dietary niche was estimated using lizard stomach contents and stable isotopes analysis of lizard tail muscle, lizard stomach contents, arthropods and plant samples (δ13C and δ15N).
Results/Conclusions
Lizard relative abundance (using only trapping data) varied widely by habitat type. For insectivorous lizards over all sites in both summers 179 individuals were caught in WS sites, 32 were caught in ecotonal sites and 79 were caught in dark soils sites. For snakes, 0 were caught in White Sands sites, 5 were caught in ecotonal sites and 9 were caught in dark soils sites. Community composition, using trapping and survey data, also varied by habitat. In WS only the three WS species (Aspidoscelis inornata, Sceloporus cowlesi, and Holbrookia maculata) were observed. At ecotonal sites we found the three WS species plus Uta stansburiana (a potential competitor) and 4 species of predatory lizards and snakes. In dark soils sites, we found 5 species of predatory lizards and snakes and 5 species of insectivorous lizards (including Aspidoscelis inornata). We are still analyzing and processing stomach content and stable isotope data, but we found that the conditions at WS are ideal for testing the NVH in the context of ecological release.