Ecosystem function and stability: The role of species diversity and environmental heterogeneity.

摘要

The amount of land with complex land-use histories and altered natural disturbance regimes is constantly expanding and understanding how these legacies affect an ecosystem's ability to function and future susceptibility to environmental perturbations is an ongoing challenge in ecology. Through a large-scale observational study of successional prairie plant communities, this dissertation explores the effects of agricultural history and gopher-mediated soil disturbance regimes on diversity-productivity and diversity-stability relationships.;Identifying clear, generalizable patterns in diversity-stability relationships is a complex challenge for a number of reasons including the lack of standardized metrics for assessing stability and a lack of understanding in how various measures of stability compare with one another. Consequently, I applied four distinct measures of stability (temporal variability, resistance, resilience, and persistence) along with two methods of quantifying each measure to the same successional grassland system in order to generate a stability profile and identify patterns of congruence or divergence between the multiple measures. I found that while species richness could enhance both temporal stability and community resistance to disturbance events, community resilience and persistence decreased with increasing plant species richness. Furthermore, although the different metrics for quantifying each stability measure yielded qualitatively similar results, some metrics appeared to be more reliable and easier to apply than others.;Finally, by choosing the most reliable metrics of stability, I assessed the effects of farming legacy and soil disturbance on the temporal variability, resistance, and resilience of plant community biomass. I demonstrated that as both the intensity of soil disturbance and the successional age of the plant communities increased, temporal variability in community biomass decreased. Community resistance to soil disturbance was higher in early successional communities irrespective of disturbance intensity. Moreover, community resilience decreased for all successional stages except under the highest levels of soil disturbance where the interaction between legacy and disturbance factors appears to maintain plant community resilience.;Collectively, these studies demonstrate the importance of explicitly considering land-use history and disturbance regimes in identifying and understanding the role biodiversity plays in both the functioning of ecosystems and in generating patterns of community stability. Therefore, in order to predict and maintain the ecological processes that sustain ecosystems and consequently the environmental services species provide to society, it is essential to expand our spatial and temporal understanding of disturbance effects on diversity-function and stability relationship.;By sampling across a gradient of agricultural abandonment and a natural gradient of soil disturbance, I was able to examine the individual and interactive effects of farming legacy and soil disturbance on the shape of the relationship between species richness and plant community biomass. As has been found in previous studies, I observed a positive correlation between species richness and community biomass. Although, in contrast to previous grassland studies, I did not observe a saturating effect in the contributions made by each additional species to community biomass. In addition, I found that the contribution made by individual species to community biomass increased with increasing soil disturbance but the rate of species contributions to biomass differed under the different crop legacies.