Diurnal Patterns of Surface Activity of a Desert Roadside Lizard Assemblage Reveal Temporal Niche Partitioning

ABSTRACT: Desert lizards are ideal animals to study temporal ecological niche partitioning of sympatric taxa. From April–September 2023, we conducted hourly low-speed road transect sampling runs continuously from about dawn to dusk (13 runs), one day each month, to document diurnal surface activity patterns of a roadside assemblage of lizards in the Sonoran Desert of southern Arizona. We obtained 1771 observations of nine heliothermic species during 78 sampling runs. Of six species having ≥20 observations, three exhibited bimodal activity, comprised of a greater mid-morning activity peak, a midday avoidance, and a lesser peak in the late afternoon, whereas the other three species exhibited unimodal activity with late morning peaks. Surface activity among lizards appeared driven by environmental cues more so than intrinsic circadian patterns; activity was greatest when temperature was 31.8 °C, solar irradiance was 433.1 W/m², and relative humidity was 43.6%. Our robust methods resolved subtle niche partitioning within a diverse diurnal lizard assemblage. Temporal patterns of surface activity should be considered when designing inventory, monitoring, and research projects.