Perennial springs in the arid Southwest support diverse aquatic communities, but are vulnerable to desiccation during severe droughts. Many formerly perennial habitats are transitioning to ephemeral habitats, and these habitat transitions may dramatically alter local community dynamics. Additionally, regional climate change models predict increased frequency and magnitude of droughts. To assess the impact of the recent severe drought (1999-2005) on desert spring biota, we sampled the aquatic insect community at French Joe spring (SE Arizona) and measured physical habitat variables seasonally between 2003 and 2008.
The spring was perennial until April 2005, when it failed and went dry for several months. In September 2005, intense monsoon rainfall recharged the spring. Since then, water levels have fluctuated greatly with several subsequent drying events. Within two months of the initial recharge, more than 29 species (mainly beetles and true bugs) had recolonized the spring. Six species lacking a drought-tolerant stage were extirpated, however, including a population of giant water bugs which has likely been isolated at French Joe since the Pleistocene. Many taxa exhibited signs of ecological release and were more abundant after the extirpation of predator and competitor taxa. Non-metric multidimensional scaling analyses revealed that community composition changed dramatically following the spring failure and recharge and that the community is continuing to change, moving away from pre-failure trajectories. Taxa richness, however, was not affected by the transition from perennial to ephemeral habitat conditions. French Joe could serve as a model system for understanding changing community and hydrologic dynamics at springs across the Southwest under intensified interannual droughts or anthropogenic aquifer depletion.