Homeostasis and compensation: The role of species and resources in ecosystem stability

A synthesis of community and ecosystem ecology should yield insights into the role of species in ecosystem function. Concepts from these subdisciplines of ecology, specifically 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. We predict that ecosystem-level properties, such as species richness, total population. biomass, and energy use, will exhibit less variability in response to environmental change than will species composition. We tested this prediction using long-term data of a desert rodent community responding to natural environmental fluctuations and of a plant community responding to experimental manipulations. 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-yr 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 J. L. Klug et al. we detected negative covariances in the rodent community, confirming the presence of compensatory dynamics.