Consumer control of plant communities in current and future environments

It has been difficult to make community-level predictions of the consequences associated with the disruption of relationships between plants and herbivores by global environmental changes. I explored the interaction between plants and their animal consumers in California annual grasslands in order to formulate predictions of plant community responses to environmental changes.; Invasion by nonnative species is often described as a component of global environmental change, in part because of its worldwide potential to undermine the integrity of longstanding interspecific associations within and among trophic levels. Focusing on the interaction between harvester ants and plants reveals that mechanisms of invasion do not necessarily reinforce one another. Harvest ants influence the distribution of most serpentine grassland plant species through the translocation of seeds and the and the construction of nutrient rich nest mounds, promoting plant communities that are distinct from the surrounding serpentine grassland, with notably higher densities of legumes and invasive annual grasses. Harvest ants are threatened with widespread displacement by invasive Argentine ants. These ants do not build mounds and do not replace the seed dispersal services provided by the native harvester ants that they displace. The implication is that invasion of serpentine grasslands by Argentine ants may directly displace native ant fauna, but concomitantly slow the encroachment of invasive grasses into these biologically significant refuges for native California flora.; California annual grasslands are inhabited by many other ubiquitous yet inconspicuous herbivores, and the activity of these herbivores influence the production, composition, and stand structure of California annual grasslands. The disruption of these plant-herbivore interactions may itself be a major driver of plant community responses to global changes. Anthropogenically-driven global environmental changes, including increased atmospheric carbon dioxide (CO2), warming, increased precipitation, and increased N deposition, directly induce species-specific changes in plant physiological properties, which in turn modify herbivore consumption patterns. These changes in herbivore feeding preferences consistently explain the direction, and often the magnitude of plant compositional responses to simulated future environments. Global changes influence the size and abundance of herbivores, and these modifications may provide a greater understanding of plant community responses to future environments.