Anthropogenic climate change is predicted to cause many extinctions worldwide. Species endemic to a single island or archipelago (“island endemics”) carry high conservation value and are known to be especially vulnerable to human impacts, but there has not yet been a global analysis of climate-driven extinction risk focused on island endemics. Furthermore, little is known regarding what factors might shape island endemics’ climatic niches and, in turn, their vulnerability to climate change.
Here, we use conifers as a model system to assess extinction risk among island endemics under climate projections for 2070. We employ the emerging technique of combining native and non-native occurrence data to model climatic conditions (i.e., niches) under which each species can sustain a population, and we also incorporate horticultural data to model the broader range of conditions that allow short-term persistence. Additionally, we explore relationships among species’ niche breadth, extinction vulnerability, and the areas of their native islands.
Results/Conclusions
Our projections indicate that some species will retain suitable climatic conditions, some will experience conditions completely precluding survival, and others will experience intermediate-risk conditions that lead to gradual population decline and eventual extinction. Extinction risk correlates strongly with the size of species’ native islands. Based on different climate change models, we report island size thresholds of 400 to 20,000 km2, below which extinction risks increase sharply. These patterns are driven by positive correlations among island area and the breadth of species’ realized, fundamental, and tolerance niches. Notably, realized and fundamental niche breadth show a strong positive correlation, even after controlling for potential sampling bias. Our results highlight management interventions needed to protect island endemics from climate-driven extinction across islands of different sizes.