Ecological processes in grasslands are largely determined by dominant species’ response to ecological drivers. In the Great Plains, large grazers selectively feed on dominant grass species, altering the composition of species and genotypes, and structure and function of grasslands. However, the degree to which grazing acts as a selective force on genetic variation in the dominant species, and whether such selection mirrors changes in community composition, represents a knowledge gap in our understanding of grasslands. Thus, our overall goal is to test whether grazing alters the genetics of a foundation grass species (Andropogon gerardii) and compare these changes on grazing effects on the accumulation of species diversity. We hypothesize that grazing acts to increase genotypic and species diversity. This knowledge will deepen our conceptual understanding of understudied linkages between evolutionary and ecological processes, and how evolutionary trajectories may mirror community responses.
Results/Conclusions
We used side-by-side grazed (30 year) and ungrazed watersheds at Konza Prairie to look for effects of grazing on genotypes and communities. To test for effects on genotypic diversity, in 2014, we collected leaf samples from 43 A. gerardii plants on both the grazed and ungrazed watersheds. Plants were genotyped and we identified ~12,000 SNPs. We found that genetic variation differed between grazed and ungrazed watersheds. STRUCTURE analyses identified 3 genetic clusters within grazed and ungrazed watersheds. However, the relative proportion of each genetic cluster differed; grazed areas contained a balanced mix of genetic clusters, and ungrazed areas had primarily only one genetic cluster. Genetic outlier analysis identified ~15 outlier SNPs showing a signature of divergent selection among grazed and ungrazed populations. To explore community response to grazing, we used long-term plant community data (1983-2014) from the same locations to look for effects of time since bison reintroduction on changes in diversity. A model selection approach revealed that while time had minimal effects on diversity in the ungrazed watersheds, diversity increased substantially with time since bison reintroduction in the grazed watersheds. These studies reveal evolutionary responses on contemporary timescales that mirror community-level processes to an ecological driver.