Spatiotemporal variation in water availability drives insect community dynamics in an urban riparian zone

Water bodies can mitigate urban heat island effects and allow terrestrial animals to access water during periods of insufficient precipitation. Because precipitation is expected to become increasingly scarce in many global regions, urban riparian areas in drylands may yield important insight into the dynamic role of water in terrestrial animal communities. Here, we first investigated the role of spatiotemporal variability in water availability in insect biomass and biodiversity in an urban riparian area—particularly, whether seasonality modulates the spatial effects of water availability. High water availability was characterized spatially by proximity to a river, and temporally by high-precipitation seasons. Second, we investigated whether the relationship between biomass and biodiversity shifts due to variation in water availability. We determined the biomass and biodiversity of an insect community across a riparian zone in Stockton, CA, USA, an urban drylands area characterized by hot, dry summers and cool, wet winters. Time (seasonality exhibiting dramatic variation in precipitation) exerted strong effects on ecological indices and a biodiversity-biomass relationship. Space (proximity to a fixed water source) had more modest effects on the community, and there was some evidence that space and time modulated the effects of one another on the community. Urban animal community dynamics may be more sensitive to larger-scale climate patterns than to local, landscape-level factors, and covariation between biomass and biodiversity may be influenced by resource (water) availability. Studying insect communities in the riparian zones of urban drylands may be critical to understanding how animal communities respond to a warmer, drier climate.