by Cameron Lukos
Adaptations, and how effective the adaptations are, allow species to have varying geographic ranges. For instance, species that have the tolerance to survive in cold climates will be able to live and survive in those conditions while others who do not have that ability will not be found. This gives different geographic ranges for all species. But our world is experiencing global climate change which means that the environments species are presented with will also change. Bocedi et al. (2013) used models to include the effect of climate change coupled with species interactions to understand these changing dynamics. To do this, they created simulations of two competing species across a linear climatic gradient that changes at different latitudes and gets warmer. Bocedi et al. gaged reproductive success by the individual’s adaptation to local climate and its location relative to global constraints. In conducting their experiment they found that in changing the strength of adaptation and competition, competition reduces genetic diversity and slows the rate of range change. They also found that one species can drive the other to extinction long after climate change has occurred. Weak selection of adaptation and low dispersal ability also caused a loss of warmer-adapted phenotypes and that geographic ranges became disjointed and lost centrally adapted genotypes.
In creating these models Bocedi et al. had to consider (1) environment and climatic tolerance, (2) population dynamics and completion, and (3) dispersal. To understand environment and climatic tolerances the experimenters ran simulations with an individual-based map lattice model. The grid was 200 rows by 200 columns with only 20% of the cells as suitable habitat. The created environment was given a linear climate gradient that increased by 0.075⁰C/column. The gradient was then shifted up to simulate climate change. The two species were modeled with potential for local adaptation affecting their chance to reproduce at a given location. For the population dynamics and competition they added in the two species having discrete generations which reproduce based on an individual-based formulation of the Ricker model. The species were not competing for space, but depending on the strength of competition, species can reduce each-others’ growth rate. Dispersal was kept at a constant equal to 0.2 and if the disperser arrived in a cell where habitat was unsuitable it died. The simulations were run 5 times using different parameter sets. The climate was held stable for 100 generations and then changed one row every two generations and then held stable again for another 100 generations. All populations were at carrying capacity in all suitable cells; each simulation had a parameter changed, such as the strength of competition.
The models were a way to illustrate the variety of ways for local adaptation and species interaction to mold and modify the response of species to climate change. The models showed a number of nonintuitive outcomes with the interplay of strength of interaction and strength of selection. Bocedi et al. observed three alternative responses of species to climate change. First, the interacting effect of climate change and a competition can drive locally-adapted species to extinction by eliminating the range entirely. Second, a competing species may continue through an episode of climate change by shifting its range, sometimes at a highly reduced distribution after the range shift. Third, a species can persist through climate change and high competition but will suffer large reductions of genetic diversity and thus allow only a warm or cool genotype to dominate the species as a whole. These results suggest that when considering species ranges in regards to climate, scientists should consider more heavily local adaptation. Species may lose the central portion of their thermal range, and climate change, local adaptation, and competition will reduce the genetic diversity of the species.
Bocedi, G., Atkins, K., Liao, J., Henry, R., Travis, J., Hellmann, J., 2013. Effects of local adaptation and interspecific competition on species’ responses to climate change. Annals of the New York Academy of Sciences 1297, 1749-6632. http://bit.ly/1zYGoNy