Niche evolution versus climate change in diversity hotspots: phylogenetic analyses in plants and animals
A fundamental question for understanding the future of Earth’s biodiversity in the face of ongoing anthropogenic climate change is: what happens when a species’ climatic niche no longer occurs within its geographic range? Three possible outcomes include: (a) the species geographic range will shift (possibly involving range expansion at the cool-edge of the range and range contractions due to local extinction at the warm edge), (b) the species will acclimate to the new conditions (e.g. if the new conditions are within its fundamental niche, the realized niche will shift to include these new conditions), and (c) the climatic niche will shift through evolutionary adaptation to the new abiotic and/or biotic conditions. In short, there will either be a niche shift or local extinction.
In this talk, I will describe new research from my collaborators and I addressing two questions: (a) how quickly do climatic niches change? (b) when climate changes, does the predominant response involve niche shifts or local extinctions? To address the first question, I will describe our research estimating rates of change in climatic niches among vertebrate species, among plant species, and among populations of both plants and animals, using time-calibrated phylogenies and GIS-based climatic data. We then compare these rates of past change to rates of projected climate change within the geographic range of each species.
To address the second question, I will describe our research on responses of montane reptile species to past climate change in the Madrean Sky Islands of southeastern Arizona, an important biodiversity hotspot in North America. This ongoing research combines inferences from museum records, field surveys, climatic data, and population genomics to test whether montane species underwent niche shifts or local extinctions in response to past climate change (with special emphasis on the Mountain Spiny Lizard).
Our results on rates of niche shifts so far show that rates of past change in climatic niches are substantially slower than rates of projected anthropogenic climate change, in both animals and plants (a pattern consistent with the observation that there are already widespread local extinctions due to present-day climate change). Our results from the Madrean Sky Islands suggest that distributional patterns in the focal species are shaped largely by niche conservatism and local extinction in response to past climate change. Overall, these results cast doubt on the idea that narrow-ranged species can simply adapt to changing climates in the next 100 years.