Evolution is expected to play a key role in species’ responses to climate change, either through adaptation to altered conditions, via the spatial evolutionary mechanisms known to impact range expansions, or both. However, it is unclear how these different evolutionary processes might interact. Additionally, in contrast to a founder population expanding its range, a population shifting its range is characterized by some initial spatial structure. For example, the population could be locally adapted along an existing biotic or abiotic gradient within the initial range. Further, the existing range edge could be characterized by a stark transition from favorable to unfavorable habitat or by a more gradual shift causing a slow decline in population size near the range edge. To understand the role of rapid evolutionary changes in range shifting populations, we constructed an individual-based model allowing for evolution in both fitness and dispersal ability. Both traits are defined explicitly by multiple loci allowing for both neutral and adaptive fluctuations in allele frequencies. Population dynamics occur in discrete patches connected by dispersal. A population’s initial range is defined by manipulating both the degree of local adaptation and the slope with which habitat quality declines at the range edge.
Results/Conclusions
Using this model, we compared the interacting effects of local adaptation within the range, the starkness of the transition from favorable to unfavorable habitat at the range edge, and speed of climate change on the dynamics of theoretical population responses. By exploring a range of parameter space along these axes, we were able to determine both the independent and combined effects of these factors. For example, both local adaptation within the range and the starkness of the transition at the range edge independently and in conjunction reduce a population’s ability to track a shifting climate. Additionally, we show that the parameters defining the initial range have important effects on the distribution of trait values in the range before climate change. These trait distributions subsequently determine the composition of phenotypes at the edge of the range shift, dramatically altering the ability of shifting populations to effectively track climate change. Thus, it is critical to consider characteristics of a species’ range and their potential interaction with evolutionary processes when making predictions of the species’ response to ongoing climate change.