Print PageFueled by a wealth of observational studies and experiments of varying size and complexity, early reviews of biodiversity-ecosystem functioning relationships have focused on the question whether diversity begets function. Following the general acceptance of a positive effect of biodiversity on different ecosystem properties (increased mean and/or reduced variance of process rates or pool sizes) interest has shifted to underlying mechanisms. This caused a debate about the importance of sampling and complementarity effects. While sampling effects are caused by the presence of influential species and the higher probability of occurrence of such a species in more diverse communities, complementarity arises as a synergistic property from the mixture of different species. Today, it is generally accepted that both types of mechanisms occur in nature and contribute to the various effects of diversity on ecosystem functioning. Yet, the underlying biological mechanisms remain elusive. In my review, I discuss biological mechanisms that can cause communities of higher diversity to function in a complementary way and identify ecosystem properties for which an investigation of such underlying mechanisms is needed. I surveyed published accounts based on a search in web of science, reference lists of existing reviews on diversity effects, and forward citations of key articles. Over 1000 articles on the functional importance of diversity were screened.
Results/Conclusions
The compiled examples for biological mechanisms include the classic idea of resource use complementarity where diverse communities use nutrients more completely and/or more efficient. This was documented for plants’ use of nitrogen and light (space), feeding behavior of decomposer macrofauna, and different microbes forming consortia to enable metabolic processes. There are also examples for temporal complementarity due to fluctuating abundances of e.g. plant or fish species over seasons. Other mechanisms involve changes in the size or physiology of individuals in reaction to competition (phenotypic plasticity resulting in complementarity), lower host densities reducing disease spread, or behavioral interactions creating synergistic effects. In conclusion, a wide range of different mechanisms causing complementarity could be identified but only a small proportion of studies in biodiversity-ecosystem functioning research explicitly addresses the biological mechanisms underlying observed effects. I argue that there is an urgent need to address mechanisms in future biodiversity experiments.
