Pockets of resistance: Response of arid‐land fish communities to climate, hydrology, and wildfire

Abstract

Abstract Disturbance regimes of arid regions throughout the world are changing along with global warming. Severity of drought associated with decreased stream discharge and increased frequency and intensity of wildfires are increasing in many of these systems. Combined, these factors can have potentially devastating effects on stream fish communities. To quantify the response of fish communities to annual variation in climate, hydrology, and wildfire, we used long‐term and spatially extensive datasets from the Gila River drainage, NM, U.S.A. Additionally, we tracked the recovery of multiple fish communities within the study area following extreme drought and associated wildfires that occurred between 2011 and 2013. Twenty‐nine years of monitoring at six sites, beginning in 1988, indicated that fish community richness and density were negatively associated with drought, as quantified by the Palmer Drought Severity Index. Ordination of fish species densities across these sites further suggested that native species were more sensitive to inter‐annual variation in climate than non‐native fishes. The resistance and resilience of fishes to drought and ash flows following the most severe series of wildfires on record between 2011 and 2013 were highly variable across sites and species. The percent of common species that were able to resist a significant decline ranged from 0 to 70%, depending on location. As of 2017, all but two species (one native and one non‐native) had recovered at one or more sites. Although we hypothesised that the response to wildfire and drought that occurred between 2011 and 2013 should vary with body size and species provenance (native or non‐native), this was not supported. Rather, resistance of fish communities to these events appeared to be driven primarily by spatial factors, such as intensity of disturbance, and resilience was driven by species ability to rapidly rebound from severely depressed numbers or immigrate from nearby refuge populations. Current climate trends suggest an increase in the intensity of disturbance associated with wildfire and drought; thus, maintenance of native biodiversity should focus on preservation of habitat integrity and connectivity among habitats that allows for recolonisation of disturbed habitats.