Declining streamflow induces collapse and replacement of native fish in the American Southwest

Abstract

Water scarcity is a global threat to freshwater biodiversity, but connecting variation in streamflow to viability of imperiled faunas remains a challenge. Here we combined time‐series modeling techniques on long‐term ecohydrological data to quantify flow–ecology relationships on native and non‐native riverine fish in the American Southwest, and simulate likely fish trajectories and “quasi‐extinction” risks in the near future. Streamflow has been declining conspicuously over the past 30 years in the Colorado and Rio Grande river basins, and year‐to‐year variation in streamflow influences the covariation between native and non‐native fish abundance. Risks of decline are high (>50%) for nearly three‐quarters of the modeled native species, and current trends in streamflow increase quasi‐extinction risk for natives (+8.5%) but reduce this risk for non‐natives (–5.9%). Hydrological changes need to be mitigated if we are to slow down the rapid replacement of native biodiversity with non‐native species in American Southwest rivers.