Climate change drives habitat specialization and local extirpation, causing niche reduction in an endemic chipmunk

Climate change is a driver of species extirpation, particularly for local endemics. The niche reduction hypothesis provides a conceptual framework to understand how the realized niche of a declining species is reduced from its historical niche to its contemporary niche due to threats. The Organ Mountains Colorado Chipmunk (Neotamias quadrivittatus australis) is an example of an endemic montane mammal for which climate change may be a threat. We used occupancy models developed for historical sites to evaluate the extent of extirpations and their causes. We used occupancy models developed for random sites to evaluate the contemporary distribution and realized niche. Our results suggest that the Organ Mountains Colorado Chipmunk has undergone broadscale extirpation (extirpated from 64% of sites) with a lower elevation range boundary contraction of 262 m in the past 30 yr. Chipmunks were extirpated from hotter and more arid biotic communities and persisted in drainages that provide cooler and more mesic conditions. Chipmunks avoided conifer forest, which were an integral part of their historical niche, suggesting that the Organ Mountains Colorado Chipmunk may have undergone a reduction in its realized niche. The Organ Mountains Colorado Chipmunk has become a de facto "functional habitat specialist" restricted to climate change refugia, further increasing its vulnerability to climate change and other threats.