Drought and Vegetation Lag Effects Influence Lizard Abundance: A 10-Year Study of Perennial and Intermittent Urban River Areas

Abstract

Animals living in urban desert ecosystems are affected by temperature extremes and altered hydrological regimes. Cities can alter both the physical and biotic environment by increasing temperature and modifying vegetation of species habitat. This study explores the ecohydrological interactions among climate, vegetation and lizard abundance along perennial and intermittent river reaches in Phoenix, Maricopa County, AZ, USA, over a decade. We calculated lizard abundance from visual encounter surveys along the Salt River and analysed their relationship with bioclimatic variables and vegetation cover, using geospatial datasets to incorporate annual and lag-year effects. We focused on diurnal insectivorous lizards including Aspidoscelis tigris (tiger whiptail), Uta stansburiana (common side-blotched lizard) and Urosaurus ornatus (ornate tree lizard) and the insectivorous and saurophagous Callisaurus draconoides (zebra-tailed lizard). Some species were more numerous along perennial compared with intermittent reaches highlighting the importance of water availability. Our findings indicated a decline in lizard abundance and richness over the study period, with abundance positively correlating with precipitation. Lizard abundance for some species was related to lagged effects from vegetation cover, emphasizing the delayed response of biotic communities to ecosystem changes. This study provides one of the few assessments of multiyear changes in urban lizard communities in a desert city and underscores the importance of understanding ecohydrological patterns. Drought conditions with low precipitation could have negative impacts on urban lizard abundance, and maintaining perennial flows and vegetation cover can benefit urban desert wildlife.