Can local-scale studies of climate, competition, and plant population dynamics teach us anything about species distributions?
Climate change can affect the abundance and distribution of a focal species by directly influencing its demographic rates, but also by altering the abundance and/or per capita effects of other species with which the focal species interacts. We studied the direct effects of precipitation and temperature on perennial plants in five semiarid plant communities, along with indirect effects mediated by plant-plant interactions, by simulating multispecies population models fit to long-term demographic data. Specifically, we tested the hypothesis that larger niche differences would decrease the strength of indirect effects of climate change. We then discuss whether the results of this work are relevant to understanding regional, scale species distributions.
In all five of the communities we studied, niche differences among the common, co-occurring species were large, and indirect effects of climate variation were weak. As a result, direct effects dominated species’ responses to simulated climate perturbations. For these species, single-species models that treat interspecific competition implicitly would perform almost as well as a multispecies model. If we were to apply this lesson directly to the question of species distributions, we might conclude that we can safely ignore competitive interactions. However, there are good reasons to be suspicious of such a logical leap: per capita competitive effects could vary dramatically across a species’ distribution and novel competitors might exert stronger indirect effects than local assemblages of stably coexisting species. Nevertheless, because plant competition is often diffuse and may not be dramatically altered by climate change, we argue that incorporating competitive interactions in species distribution models should be a lower priority than devising direct tests of model predictions and considering the potential for evolutionary adaptation.