Emergent properties of a Chihuahuan desert ecosystem

In this dissertation, long-term data from sites in the Chihuahuan desert were used to explore the relationship between resource availability and ecosystem dynamics.; The first chapter explores the effect of both limiting resources on resource/consumer dynamics. I examined temporal correlations between precipitation, plant cover, and rodent density, with varying time lags using long-term data from two sites in the Chihuahuan desert of North America: the Sevilleta Long-term Ecological Research site (LTER), New Mexico, USA and a site near Portal, Arizona, USA. I also calculated the spatial correlations in precipitation, plant cover, and rodent dynamics among six sites, five at Sevilleta and one at Portal. Spatial correlations in plant cover and rodent populations between sites reflected the localized nature of summer rainfall, so that sites with highly-correlated summer precipitation exhibited higher correlations in plant cover and rodent populations. In general, these results indicate that limiting resources influence consumer dynamics, but these dynamics also depend crucially on the biotic interactions in the system.; The second chapter attempts to understand how processes at the community-level can affect ecosystem dynamics. The concepts of species compensation and ecosystem homeostasis can be linked by analyzing the effect of changes in the abundance of species on ecosystem processes. Compensatory changes in species populations in response to environmental fluctuations can maintain an approximate steady state between rates of resource supply and resource consumption. For the rodents, species composition was twice as variable as the ecosystem properties. This result was the same for both the analysis of variability around the 22-year average and the analysis of variability from one time period to the next. For the plant communities, species composition was more variable among treatments in most years than stem count or species richness. Using the variance ratio proposed by Klug et al. (2000) we detected negative covariances in the rodent community, confirming the presence of compensatory dynamics.; The third chapter examines the processes which influence the ability of a community to compensate for disturbances. For species compensation to occur, species with the necessary niche requirements must be available to the community. (Abstract shortened by UMI.)...