Effects of interspecific interactions on the structure and dynamics of plant communities in an arid ecosystem

Interactions among species are ubiquitous in nature. Trophic, competitive, and facilitatioe interactions affect patterns of species diversity, community structure, and fluxes of materials and energy in all ecosystems. In arid ecosystems species interactions appear to play a crucial role in certain aspects of plant community structure, but their effects on processes that maintain species diversity (e.g., community dynamics) and ecosystem functioning are less understood. Here, I investigate the effects of these three types of inter-specific interactions on the structure and rates of temporal change of plant communities and on nutrient fluxes in a water and nutrient limited and ecosystem. First, I examine how competitive and facilitatioe interactions determined by dominant species influence the species diversity and stability of subdominant communities. To do so, I consider how facilitation by the invasive native shrub ( Larrea tridentata) affects subdominant communities, compared to the competitive effects exerted by the native grass (Bouteloua eriopoda ). My findings suggest that species diversity and community stability can respond to shifts in interspecific interactions, where facilitation decreases species diversity and community stability, and competition enhances both community properties. Second, I assess the effects of trophic interactions exerted by small mammals on the structure and dynamics of the plant communities of a desert system extremely limited in water and nutrient availability. My results show that bottom-up forces limit the growth of producers and consumers to the point where tropic interactions have virtually no effect on plant communities. Third, I investigate the effects of trophic interactions on the availability of a limiting nutrient (nitrogen) in the soil in three sites in the Chihuahuan desert. Rodents increased soil nitrogen between 15 and 30% during prolonged dry seasons, apparently via metabolic waste outputs. Overall, I show that in this arid system competitive and facilitative interactions among plants are important determinants of the patterns of species diversity and dynamics of the plant communities. Although, trophic interactions only affected plant communities to a minor extent, they did influence ecosystem processes.