A Rattlesnake on the Brink: Global Change and its Impacts on Short-Range Biodiversity Endemics

Environmental change at global scales profoundly impacts biodiversity, particularly those elements identified as ‘short range endemics’ (SREs), as they possess life history traits that render them acutely vulnerable to climate fluctuations. The ecological niche of the federally listed sky-island SRE New Mexico Ridge-nosed Rattlesnake (Crotalus willardi obscurus) is impacted by extended drought and intense forest fire. It is constrained by aridity at lower elevations and loss of habitat as altitude increases. Here we coalesce demographic, climate, and molecular genetic data to evaluate its long term persistence. A long-term mark/recapture dataset assessed demographic status, evaluated impacts of a shifting fire regime on survival, and gauged its dynamics using stochastic population models and three fire intensity scenarios. Annual survival was estimated at 0.70 (± 0.10), while a deterministic (null) population model underscoring a declining intrinsic growth rate (r = -0.1). Using contemporary fire patterns and stochastic population simulations, intrinsic growth decreased significantly in this SRE and time to extinction was significantly shorter than expected (i.e., 133 ± 23 years). Furthermore, a substantial northwestern shift of 753 km was predicted in its climate envelope by 2080, with core habitat pushed to the envelope's trailing edge. Finally, lack of movement among populations is more pronounced than mark/recapture efforts suggest, with microsatellite data defining abrupt demographic isolation among populations. The Ridge-nosed Rattlesnake is not only a key sky-island SRE at the precipice of an extinction vortex, but is a bellwether for the collapse of the Madrean pine-oak ecosystem, one of Earth’s three recognized “megadiversity” centers.