Recent Graduate The University of Chicago Los Altos, California, United States
With the advance of climate change, understanding the impact of climate on species ranges has important consequences for conservation. The true sagebrushes, 21 endemic species of Artemisia section Tridentatae in North America, are the keystone species of the sagebrush steppe, one of the largest and most endangered ecosystems on the continent. Their broad geographic range paired with the availability of occurrence data of the genus provide a good system to study the climatic controls of species ranges. To identify the climatic limitations on species ranges of each species in the section Tridentatae, I trained a climate envelope model to predict the range of each species. Using the highest density of occurrence as a proxy for each species’ optimal niche, I calculated correlations between range area and climatic variables. I then conducted a principal component analysis on the optimal niche of each species to find the variables with the strongest influence on distribution. I trained a `bioclim` model in R with each species’ occurrence dataset and the variables identified from the PCA to form a climate envelope model for each species.
I show that climatic variables are a major driving factor behind the latitudinal gradient of species richness observed in the section. The size of each species’ range seems to only be correlated with temperature minima. The principal component analysis shows that minimum temperatures explain 42% of the variance in range, while precipitation (seasonality and quantity) explains 27% of the variance. The climate envelope models project fundamental niches that extend past the observed occurrences of the species. This is expected as other factors such as soil composition and human impacts may affect range in ways that are not accounted for in the models. These results indicate that Artemisia section Tridentatae is more susceptible to changes in temperature than precipitation. This model can be used to forecast where the fundamental niche of the species’ will shift to help lead conservation managers.