Extreme drought impacts drove local extinction in a social rodent.

Wildlife populations worldwide are increasingly exposed to climatic extremes, yet demographic mechanisms linking environmental variability to local extinction remain poorly understood. We evaluated the population dynamics of a degu (Octodon degus) population in central Chile over a 12-year period (2009-2020) encompassing a decade-long megadrought. Using capture-mark-recapture models, we estimated apparent survival, recruitment, and population growth rates and assessed their relationships with climatic and ecosystem variables. Population growth remained positive throughout most of the study period despite prolonged drought conditions, indicating resistance to long-term environmental stress. However, in 2019, an extreme drought year with markedly reduced precipitation and resource availability, gross primary productivity (GPP) crossed a critical threshold (a tipping point). As a result, survival and recruitment declined sharply, the population underwent an abrupt state shift and rapid collapse, and ultimately went locally extinct. Our analyses indicate that variation in GPP was the strongest predictor of both survival and recruitment, highlighting the importance of resource availability in mediating demographic responses to drought. These results show that the extreme environmental conditions in 2019 acted as the proximate driver of extinction, rather than a cumulative effect of the preceding megadrought. We discuss how species-specific traits, including short lifespan, seasonal reproduction, and social organization, may limit the ability of degus to buffer consecutive demographic failures under extreme conditions, contributing to threshold-like population collapse. Our findings suggest that populations may persist under prolonged adverse conditions yet remain vulnerable to rare but severe environmental events, emphasizing the importance of extreme climatic variability in driving local extinction risk.