American Society of Naturalists

Christopher Weiss-Lehman and Allison Shaw (Jan 2020)

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Spatial population structure inhibits range shifts via impacts on eco-evolutionary dynamics of dispersal and adaptation

Can rapid evolution save species from climate change?

Species moving to track climate change have revealed an interesting phenomenon that scientists hope could help them as climate change continues. As species move to track the environmental conditions to which they are adapted, many have undergone rapid, evolved increases in traits related to movement (e.g. limb length or seed size and shape). These changes could substantially improve species’ abilities to track changing environmental conditions, but new research from Drs. Christopher Weiss-Lehman and Allison Shaw at the University of Minnesota suggest it could also lead to further problems down the road.

Dr. Weiss-Lehman, now at the University of Wyoming, created a model in collaboration with Dr. Shaw to test the relationship between evolution of dispersal (i.e. traits related to movement and settlement) and extinction risk due to climate change. All populations in the model rapidly evolve increased dispersal, allowing them to keep pace with changing environmental conditions. However, Drs. Weiss-Lehman and Shaw noticed an odd pattern. Under some scenarios, populations still face extremely high extinction risks despite rapid evolution of dispersal. In populations structured by adaptation to variable local conditions, increased dispersal leads to the increased exchange of genetic material among subpopulations. This results in greater genetic similarity throughout the population and a corresponding reduction in adaptation to variable local conditions. This loss of adaptation to local conditions reduces population performance and substantially increases population extinction risk in such scenarios.

Thus, while rapid evolution of dispersal can allow species to better track climate change, it can also increase population extinction risk by reducing the degree of adaptation to local conditions. While predictions from models such as this can provide important insights for conservation in the face of climate change, more research is urgently needed to better understand how these model predictions will play out for real species.

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Abstract

Climate change is an escalating threat facing populations around the globe, necessitating a robust understanding of the ecological and evolutionary mechanisms dictating population responses. However, populations do not respond to climate change in isolation, but rather in the context of their existing ranges. In particular, spatial population structure within a range (e.g. trait clines, starkness of range edges, etc.) likely interacts with other ecological and evolutionary processes during climate-induced range shifts. Here, we use an individual-based model to explore the interacting roles of several such factors in range shift dynamics. We show that increased spatial population structure (driven primarily by a steeper environmental gradient) severely increases a population's extinction risk. Further, we show that while evolution of heightened dispersal during range shifts can aid populations in tracking changing conditions, it can also interact negatively with adaptation to the environmental gradient, leading to reduced fitness and contributing to the increased extinction risk observed in populations structured along steep environmental gradients. Our results demonstrate that the effect of dispersal evolution on range shifting populations is dependent on environmental context and that spatial population structure can substantially increase extinction risk in range shifts.