Connecting community assembly mechanisms to ecosystem function
One recent and important application of community ecology is the focus on understanding how ecological communities contribute to ecosystem function and services. There have been a large number of experimental and observational studies correlating diversity with measures of ecosystem function such as primary productivity, and these studies tend to find a positive (albeit variable) relationship. Although a number of mechanisms have been proposed for this biodiversity-ecosystem function relationship, most rather heuristically invoke niche-partitioning of resources and competitive outcomes. These basic mechanisms are the basis of most coexistence theory explaining species diversity, and so we explore the influence of coexistence mechanisms on ecosystem function.
The focus on species richness and composition in studies of ecosystem function allows them to be directly connected to theoretical models of community assembly. We used consumer-resource models in multiple patches within a metacommunity to simulate both niche and neutral assembly of communities and the effect on biomass production. Under this framework we asked how varying assembly dynamics, environmental heterogeneity, nutrient availability, resource consumption efficiency and regional species pool affect ecosystem function (biomass production). Since coexistence mechanisms and diversity are often spatially structured, we also explore scale dependency of ecosystem function patterns.
Our results suggest that community assembly dynamics may alter the strength and direction of the biodiversity-ecosystem function relationship. In our models, biomass production from neutrally-structured communities tended to be less variable across replicates than biomass production in niche-structured communities. However, because additional, ecologically-identical species add little to ecosystem function, neutral communities had relatively weak biodiversity-biomass production relationships, in contrast with niche-structured communities. In addition the distribution of traits, such as the ratio of specialist to generalist species, in the regional species pool was an important determinant of function. These results suggest that choices about the species used in ecosystem function experiments can impact the shape and strength of the observed relationship. Because current experiments can only sample a small range of the possible conditions, models such as this allow us to explore assembly-function relationships more fully and assist in developing predictive relationships between assembly, species richness, and ecosystem function.