Herbivory dampens precipitation effects on plant performance in a mixed-grass prairie ecosystem

Karen Castillioni and Lara Souza, Oklahoma Biological Survey and Department of Microbiology and Plant Biology, University of Oklahoma, Norman, OK, Michael Patten, Ecology Research Group, Faculty of Biosciences and Aquaculture, Nord University, Steinkjer, Norway

Background/Question/Methods
Climate and herbivory shape grassland communities. With climate change co-occurring with disturbances like herbivory, understanding how grasslands respond to alterations in these combined drivers may aid in projecting future changes in grasslands ecosystems. We used an experimental precipitation gradient combined with mimicked acute herbivory (clipping once a year) to examine 1) whether herbivory enhances precipitation effects on plant performance and 2) the role of species identity influencing plant performance patterns.
Results/Conclusions
We found that acute herbivory reduced the strength of precipitation effects on plant performance. Conversely, when herbivores were absent, precipitation effects were stronger and indirect through abiotic change first, followed by biotic. Though, in both scenarios, biotic variables were key mediators of plant performance to precipitation by directly promoting changes in overall plant height and abundance. Biotic variables promoted most species-specific performance, except for a single dominant species. For some C3 plant species, their performance only increased through biotic variables in the absence of herbivory, demonstrating the importance of habitat amelioration by neighbors. Our experiment demonstrates that plant performance is directly shaped by biotic variables, and that inclusion of herbivory as a disturbance to an altered precipitation scenario lessens positive impacts of biotic structure on species performance to climate change.