Biodiversity and Ecosystem Functioning: Maintaining Natural Life Support Processes

Critical processes at the ecosystem level influence plant productivity, soil fertility, water quality, atmospheric chemistry, and many other local and global environmental conditions that ultimately affect human welfare. These ecosystem processes are controlled by both the diversity and identity of the plant, animal, and microbial species living within a community. Human modifications to the living community in an ecosystem – as well as to the collective biodiversity of the earth – can therefore alter ecological functions and life support services that are vital to the well-being of human societies. Substantial changes have already occurred, especially local and global losses of biodiversity. The primary cause has been widespread human transformation of once highly diverse natural ecosystems into relatively species-poor managed ecosystems. Recent studies suggest that such reductions in biodiversity can alter both the magnitude and the stability of ecosystem processes, especially when biodiversity is reduced to the low levels typical of many managed systems. Our review of the available evidence has identified the following certainties concerning biodiversity and ecosystem functioning: • Human impacts on global biodiversity have been dramatic, resulting in unprecedented losses in global biodiversity at all levels, from genes and species to entire ecosystems; • Local declines in biodiversity are even more dramatic than global declines, and the beneficial effects of many organisms on local processes are lost long before the species become globally extinct; • Many ecosystem processes are sensitive to declines in biodiversity; • Changes in the identity and abundance of species in an ecosystem can be as important as changes in biodiversity in influencing ecosystem processes. From current research, we have identified the following impacts on ecosystem functioning that often result from loss of biodiversity: • Plant production may decline as regional and local diversity declines; • Ecosystem resistance to environmental perturbations, such as drought, may be lessened as biodiversity is reduced; • Ecosystem processes such as soil nitrogen levels, water use, plant productivity, and pest and disease cycles may become more variable as diversity declines. Given its importance to human welfare, the maintenance of ecosystem functioning should be included as an integral part of national and international policies designed to conserve local and global biodiversity. Cover photo credits clockwise from top left: