Long-Term Population Monitoring Reveals Changes in Mesocarnivore Occupancy in Response to Severe Drought

Rapid shifts in climate conditions can disrupt disturbance regimes and generate novel spatial conditions that have consequences for wildlife. In the montane Sierra Nevada range of California, USA, many species occur in sympatry, with local variation in elevation, climate conditions, and forest structure allowing species that may compete with each other to persist. However, shifting climate conditions in this region have potential impacts for species persistence and coexistence. From 2012 to 2015, a historic drought in California resulted in < 5% of expected snowpack and atypically warm winter conditions. These climatic conditions were thought to impact mesocarnivores, with particularly negative effects for species occurring at their range limits. Understanding how rapidly shifting conditions may affect species occurrence and persistence provides an opportunity to guide contemporary conservation efforts and better understand how continued change may imperil sensitive species. We examined the effects of this historic drought and contemporary forest structure on the occurrence of four sympatric mesocarnivores: Pacific martens (Martes caurina), fishers (Pekania pennanti), gray foxes (Urocyon cinereoargenteus), and ringtails (Bassariscus astutus). We used long-term monitoring data in a dynamic spatial occupancy framework to identify the consequences of a historic drought event on the occurrence of these mesocarnivores and predict the effects of continued climate change on their persistence. We found that climate-sensitive martens and fishers, who occur at the warm edges of their ranges within this system, generally exhibited declines in occupancy following warmer, drier years while gray foxes and ringtails thrived in these atypical conditions. Ringtails were the only species predicted to benefit from future changes in climate conditions, while fishers, gray foxes, and martens were predicted to decline under all climate change scenarios. Our work demonstrates the importance of identifying species-specific responses to change and the potential consequences of climate change for sympatric communities.