The relationships between diversity, stability and productivity have been the subject of intense debate in the ecological literature for at least the last half century. The contemporary focus on biodiversity and ecosystem functioning has emphasised the role of diversity in controlling the productivity and stability of communities e.g. species assembly experiments and related theoretical studies have shown a positive correlation between diversity and both productivity and stability. On the other hand earlier work emphasised the impact of factors such as productivity and disturbance on diversity. For example, the hump-backed model asserts that diversity is highest at intermediate levels of productivity whilst the intermediate disturbance hypothesis (IDH) holds that local diversity is promoted by low levels of disturbance but reduced at high levels. More recently there has been (renewed) recognition that all three factors are interdependent and are determined by the local co-evolution of species assemblages in different settings.

Here we present a generic model of resource competition and co-adaptation between species in a local community in which species compete for a single resource and a fluctuating environmental variable determines the relative competitive ranking of species. Coexistence of species is therefore possible via temporal resource partitioning, but in the model this is mediated by the competing effects of stochastic extinction and the immigration of novel phenotypes from a regional species pool. The model is simulated in environments with varying levels of autocorrelation/variability, but with the resource supply rate held constant. Aggregating these simulations builds a picture of diversity-stability-productivity relationships that might be observed in a region with a given level of resource supply, but local variation in the properties of the environmental variable. These relationships broadly agree with the IDH and hump-backed models. In contrast when we vary resource levels (indicative of regional/large-scale gradients) we typically find increasing diversity-stability, diversity-productivity relationships. Finally, by turning off the immigration component, the model is used to study species assembly scenarios with results confirming the positive impact of diversity on stability and productivity.

Our results suggest that many of the documented relationships between diversity, productivity and stability can be viewed as different facets of a fundamental competition for resources.