Environmental drivers of arthropod communities across the endangered predator Gambelia sila's current and historic range

Describing the habitat needs of endangered species is a major focus of applied conservation research. The blunt-nosed leopard lizard (Gambelia sila (Stejneger, 1890)) is a flagship endangered species endemic to the San Joaquin Valley of California, USA. Arthropods are an important component of G. sila's diet and of many other listed vertebrate species in Californian drylands. We examined the drivers of abundance, richness, and composition across the current and extirpated ranges of the blunt-nosed leopard lizard G. sila for four arthropod communities: ground-active, shrub-canopy active, open area active, and aerial. We found no evidence for lower arthropod abundance or species richness at sites from which G. sila has been extirpated. In contrast, the ground-active arthropod and beetle communities were less abundant at sites with current populations of G. sila after accounting for environmental variation. Thus, prey availability—at least at the community level and for the taxonomic groups considered—would not likely be a factor constraining future repopulation efforts for G. sila into its historical range. Beta-diversity partitioning analyses indicated that a regional approach to conservation is necessary to conserve arthropod biodiversity across the San Joaquin Valley. Increasing aridity lowered abundance and species richness at fine scales for most communities tested and was also related to spatial composition across the region. Thus, in terms of G. sila conservation and restoration, sites with the lowest current and projected future aridity should be prioritized to maximize the abundance and richness of co-occurring ground-active arthropod and beetle communities.