Ecosystem Processes

Ecosystem processes (EP) are changes in the flows of materials in an ecosystem, resulting from the interactions among organisms and with their physico-chemical environment (Mace et al. 2012). Examples of these processes include photosynthesis, plant nutrient uptake, microbial respiration, nitrification, denitrification, nitrogen fixation, plant transpiration, etc.

EP are important because they influence the rates of ecosystem functions (EF) such as plant productivity, maintaining soil fertility and water quality, as well as other local and global environmental conditions that ultimately affect human welfare and in that way lead to ecosystem services (ES) (Naeem et al. 1999). The occurrence of these processes is controlled mainly by the functional composition and diversity of an ecosystem (Tilman et al. 1997; Diaz and Marcelo 2001). Thus, factors that change ecosystem composition such as invasion by exotic organisms, atmospheric nitrogen deposition, predator mortality, extinction of species, natural disturbances such as fire etc. are likely to affect EP. Also, the loss or addition of species with different functional traits may have different impacts (positive, neutral or negative) on particular ecosystem processes (Tilman et al. 1997; Vitousek 1990; Hooper et al. 2005).

It is widely considered that it is important to preserve as much biodiversity as possible in order to sustain EP which in turn results in the proper functioning of ecosystems (EF). This is because many EP are sensitive to losses in biodiversity (Naeem et al. 1999; Cardinale et al. 2006). The table below shows the relationship between EP and EF. This relationship is best explained as one or more EP combining to produce an EF.

Table. The relationship between ecosystem processes and ecosystem functions: some examples

Table 1.JPG

*  Soil bioturbation is generally defined as the turning and churning of soil sediments by organisms such as earthworms (Gabet et al. 2003).

References

Cardinale BJ, Srivastava DS, Duffy EJ, Wright PJ, Downing AL, Sankaran M, Jouseau C, 2006. Effects of biodiversity on the functioning of trophic groups and ecosystems. Nature 443, 989-992.

Diaz S, Marcelo C, 2001. Vive la difference: plant functional diversity matters to ecosystem processes. Trends in Ecology & Evolution 16 (11): 647-655.

Hooper DU, Chapin F, Ewel JJ, Hector A, Inchausti P, Lavorel S, Lawton JH, Lodge DM, Loreau M, Naeem S, Schmid B, Setälä H, Symstad AJ, Vandermeer J, Wardle DA, 2005. Effects of biodiversity on ecosystem functioning: A consensus of current knowledge. Ecological Monographs 75: 3–35.

Hooper DU, Vitousek PM, 1997. The effect of plant composition and diversity on ecosystem processes. Science 277: 1300-1305.

Mace GM, Norris K, Fitter A, 2012. Biodiversity and ecosystem services: A multi-layered relationship. Trends in Ecology and Evolution 27 (1): 19-26.

Naeem S, Costanza R, Ehrlich PR, Golley FB, Hooper DU, Lawton HJ, O’Neill RV, Mooney HA, Sala OE, Symstad AJ, Tilman D, 1999. Biodiversity and ecosystem functioning: Maintaining natural life support processes. Issues in Ecology 4. 14 pp

Tilman D, Knops J, Wedin D Reich P, Richie M, Siemann E (1997). The influence of functional diversity and composition on ecosystem processes. Science 277: 1300-1302.

Vitousek PM, 1990. Biological invasions and ecosystem processes: Towards an integration of population biology and ecosystem studies. Oikos 57: 7-13.