Carbon isoscapes of rodent diets in the Great Plains USA deviate from regional gradients in C4 grass abundance due to a preference for C3 plant resources

( )Diet is an ecological attribute that species may adjust to cope with changing environments and may indicate how a population responds to changes in resource availability. In the Great Plains, plants utilizing the C-4 photosynthetic pathway may increase in abundance in the future because of their high tolerance for warm and dry environments, which are projected to increase. How increased C-4 abundance will influence grassland food webs remains unknown. Here, we evaluate how rodent diets vary relative to C-4 plant biomass at the regional scale of the southern Great Plains in the U.S. We measured delta C-13 values of hair from 534 individuals of 14 rodent species. Resulting isoscapes of delta C-13 values were statistically compared to three proxies for local abundance of C-4 grasses across the region. Overall, diets of most rodent species were dominated by C-3-derived resources with a few species relying on C-4 resources. Ordinary least squares linear regressions indicate that proxies for regional abundance of C-4 grasses explain very little of the variance in delta C-13 values in hair for the entire rodent community, however the isoscape of rodent hair delta C-13 values does broadly correspond to that for delta C-13 values of soil organic matter. The difference between median delta C-13 values of granivores and folivores is significantly and highly correlated with SOM delta C-13 values. Results from this study can be used as a baseline for characterizing dietary shifts in response to environmental change both in the geological past and in the future, and they identify which dietary categories may be most sensitive to future changes in the regional abundance of C-4 grasses.