The Princeton Guide to Ecology

Forecasts of ongoing biodiversity loss prompted ecologists in the early 1990s to question whether this loss of species could have a negative impact on the functioning of ecosystems. Ecosystem functioning is an umbrella term for the processes operating in an ecosystem, that is, the biogeochemical flows of energy and matter within and between ecosystems (e.g., primary production and nutrient cycling). The first general phase of research on this topic addressed this question by assembling model communities of varying diversity to measure the effects on ecosystem processes. The results of the meta-analyses of this first wave of studies show that biodiversity generally has a positive but saturating effect on ecosystem processes that is remarkably consistent across trophic groups and ecosystem types. These relationships are driven by a combination of complementarity and selection effects with complementarity effects nearly twice as strong as selection effects overall. However, diverse communities rarely function significantly better than the best single species, at least in the short term. In the longer term, biodiversity can provide an insurance value similar to the risk-spreading benefits of diverse portfolios of financial investments. The effects of biodiversity on ecosystem functioning may have been underestimated by the first phase of research because of the short duration of many studies and the focus on singleecosystem processes in isolation rather than a consideration of all important ecosystem functions simultaneously. The next phase of research will focus, in part, on whether the benefits of biodiversity seen in experiments translate to real-world settings.

biodiversity. A contraction of biological diversity that encompasses all biological variation from the level of genes through populations, species, and functional groups (and sometimes higher levels such as landscape units)

complementarity effect. The influence that combinations of species have on ecosystem functioning as a consequence of their interactions (e.g., resource partitioning, facilitation, reduced natural enemy impacts in diverse communities)

ecosystem functioning. An umbrella term for the processes operating in an ecosystem

ecosystem processes. The biogeochemical flows of energy and matter within and between ecosystems, e.g., primary production and nutrient cycling

ecosystem service. An ecosystem process or property that is beneficial for human beings, e.g., the provision of foods and materials or sequestration of carbon dioxide

selection effects. The influence that species have on ecosystem functioning simply through their speciesspecific traits and their relative abundance in a community (positive selection effects occur when species with higher-than-average monoculture performance dominate communities)

Darwin, in On the Origin of Species, initially proposed that changes in biodiversity could affect ecosystem functioning if niche space is more fully occupied in

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