Reconstructing Climate Using the Area of Sympatry of Species' Geographic Ranges
Collaborators: David L. Fox and David Polly, University of Indiana
Geographic distributions of extant terrestrial mammals are determined in part by the climatic conditions tolerated by constituent populations, which is a measure of the ecological niche of the species. Assuming niche conservatism, past populations of a species should have had the same climate tolerances as extant populations, thus past biogeographic distributions for extant species might be used to estimate paleoclimate quantitatively. The Quaternary fossil record of small mammals in the Great Plains is a good test case for this approach as many extant species have multiple occurrences over the last million years. We have developed a GIS based method that uses modern species ranges and environmental parameters that relate quantitatively to extant species distributions in North America (e.g., mean annual temperature or MAT and mean annual precipitation or MAP). Geographic ranges for 92 extant species of rodents, lagomorphs, and soricomorphs were used to determine climatic conditions where species ranges overlap. Forty-two fossil collections in the Great Plains contain at least three of the 56 extant species in the region with fossil occurrences, potentially allowing us to constrain
paleoclimate for those collections. We assess reliability of this method by varying the number of extant species for a given location used to determine range overlap and the distribution of climate variables in the area of overlap then compared estimated and known values. For locations spanning the region, we rarefied complete extant species
lists to sample sizes of 20, 15, 10, 5, and 3 species and at each sample size estimated climate variables from range overlaps for 100 randomly sampled replicates, yielding 500 total replicates at each location. Accuracy of climate estimates increased with sample size up to 10 species, but more than 10 species did not improve accuracy substantially.
Comparison of calculated MAT values relative to modern MAT values at each fossil's geographic location. Dashed line indicates no difference between modern and calculated ancient MAT values. Calculated values are superimposed on the global oxygen isotope record of benthic foraminifera (solid gray line) (Zachos et al., 2001).