Interplay between competition and evolution in invaded and native plant communities

Daniel Atwater, The University of Montana

Abstract

The distributions and abundances of organisms are affected by ecological processes, such as competition, predation, and abiotic stress, and these processes can also produce rapid evolutionary change in plant communities. Although our understanding of ecological and evolutionary interactions is growing, so far little is known about how competition among plants interacts with evolution to shape communities. In my dissertation, I use species invasions to investigate the evolutionary and ecological consequences of plant interactions and their effects on plant community assembly.

In my first chapter, I investigated complex ecological interactions between Euphorbia esula, an invasive plant, and Balsamorrhiza sagittata, a native plant. I found that direct negative effects of Euphorbia on Balsamorrhiza, due to competition, were greatly reduced by indirect positive effects. In the second chapter, I investigated whether selection favored competitive "suppression" or "tolerance" strategies in the native Pseudoroegneria spicata when competing with the invasive Centaurea stoebe. I found that tolerance had far greater fitness benefits than suppression. This observation has important consequences for understanding the outcome of evolution in plant communities. In my third chapter, I investigated the ecological consequences of intraspecific diversity in Pseudoroegneria. I found that functional diversity within the species increased ecosystem productivity, and that this pattern was strongest for ecotypes from mesic environments, suggesting that adaptive variation influences emergent consequences of intraspecific interactions. Finally, in my fourth chapter I found evidence that selection by Euphorbia on native and invasive grasses influenced how those grasses responded to other competitors, herbivory, and changes in resource availability. I also found evidence that this selection varied among sites in a manner akin to a geographic mosaic. Together, these chapters demonstrate how plant invasions can inform our understanding of interactions between ecological and evolutionary processes that affect plant community assembly.