Network complexity and ecosystem functioning
Earth’s biota regulates numerous fluxes of energy and matter, including carbon uptake, nutrient cycling and oxygen production. When measured at local scales, these are referred to as ‘ecosystem processes’ and determine the functioning of ecosystems. Although it might seem intuitive that a suite of functionally diverse organisms is needed to sustain ecosystem functioning, it is only in the last two decades that the relationship between biodiversity and ecosystem functioning (B-EF) has received detailed scientific interest. Besides its theoretical and intellectual appeal, much of B-EF research has been motivated by the alarming rates of species loss seen across the globe and the demand to maintain the goods and services these species supply to humans. The principal goals of B-EF research have been to investigate how biodiversity and ecosystem functioning are linked and to understand the mechanisms that underpin the relationship.
In recent years, several studies (e.g. Montoya et al. 2003) have diverged from the approaches used in the earlier, pioneering B-EF research. These early studies typically focussed on species richness as the measure of biodiversity, measured only single process rates and focussed on competitive or facilitative interactions within guilds. By contrast, the newly emerging studies have moved the emphasis toward considering alternative metrics of biodiversity (e.g. functional groups), multiple processes and interactions within the wider ecological network (e.g. food web). It is becoming increasingly apparent that these three topics have to be addressed if B-EF research is to become a predictive science that can forecast the effects of species loss in the complex, multitrophic systems that we encounter in nature. Consequently, the consideration of traits, multiple processes and multitrophic interactions is now rapidly coming to the fore in B-EF research (see Reiss et al. 2009).