Integrating space into biodiversity and ecosystem function studies: Spatial averaging vs. spatial dynamics in aquatic microcosms

Background/Question/Methods

Studies of biodiversity and ecosystem functioning have proliferated in the last 20 years. However, studies of how spatial structure alters biodiversity and ecosystem functioning are few in number. Loreau, Mouquet and Gonzalez in a 2003 paper proposed the idea of spatial insurance that could help stabilize biodiversity, and noted the important distinction between the effects of simple spatial averaging and systems where there was a compensatory spatial dynamic that maintained biodiversity. A published laboratory microcosm study on protists and algae in aquatic microcosms tested the effects of dispersal and habitat (spatial) heterogeneity across patches on biodiversity. Here we used this experiment to test the effects of changes in biodiversity on 14 different ecosystem functions. Tests examined how ecosystem functions were altered by dispersal treatments and manipulation of resources available in different patches (spatial habitat heterogeneity).

Results/Conclusions

Changes in species composition were marked among different treatments, especially when the types of resources available to aquatic communities were altered. One resource type (decaying wheat seeds) produced phosphorous enrichment that led to increased algal abundance, increased photosynthesis and consequently to decreased carbon dioxide levels and increased dissolved oxygen levels in daylight conditions. The other resource type (leaf litter) produced more of a detrital community, dominated by bacterivores. Trophic structure also varied among the resource types. Of the 14 ecosystem functions several showed simple spatial averaging across habitat patches that led to an average level of functioning. However, productivity and decomposition both showed dynamics that could not be explained by spatial averaging, and likely indicate the involvement of a spatial dynamic such as mass effects. The results challenge us to identify factors behind such differences among different ecosystem functions and the characteristics of the species or functional groups that are responsible for producing spatial insurance of ecosystem functions.