Phenotypic diversity and stability of ecosystem processes

The resistance of an ecosystem to perturbations and the speed at which it r ecovers after the perturbations, which is called resilience, are two import ant components of ecosystem stability. It has been suggested that biodivers ity increases the resilience and resistance of aggregated ecosystem process es. We test this hypothesis using a theoretical model of a nutrient-limited ecosystem in a heterogeneous environment. We investigate the stability pro perties of the model for its simplest possible configuration, i.e., a syste m consisting of two plant species and their associated detritus and local r esource depletion zones. Phenotypic diversity within the plant community is described by differences in the nutrient uptake and mortality rates of the two species. The usual measure of resilience characterizes the system as a whole and thus also applies to aggregated ecosystem processes. As a rule t his decreases with increased diversity, though under certain conditions it is maximum for an intermediate value of diversity. Resistance is a property that characterizes each system component and process separately. The resis tance of the inorganic nutrient pools, hence of nutrient retention in the e cosystem, decreases with increased diversity. The resistance of both total plant biomass and productivity either monotonically decreases or increases over part of the parameter range with increased diversity. Furthermore, it is very sensitive to parameter values. These results support the view that there is no simple relationship between diversity and stability in equilibr ium deterministic systems, whether at the level of populations or aggregate d ecosystem processes. We discuss these results in relation to recent exper iments. (C) 1999 Academic Press.