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, soil fertility, water quality and other local and global environmental conditions that ultimately affect human welfare and in that way lead to 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 result 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). Table 1 shows the relationship between EP and EF. This relationship is best explained as one or more EP combining to produce an EF.
Table 1 The relationship between ecosystem processes and ecosystem functions: some examples
|Photosynthesis and plant nutrient uptake
|Microbial respiration and soil & sediment food web dynamics-see picture below
|Population control through trophic-dynamic relations
|Storage and recycling of nutrients by living organisms-see video below
|Plant transpiration and water uptake by plant roots
|Biogeochemical cycles in ecosystems (e.g., CO2/O2 balance, ozone layer etc.)
|Rock weathering, *soil bioturbation plant, colonisation and accumulation of organic matter
*Soil bioturbation is generally defined as the turning and churning of soil sediments by organisms (Gabet et al. 2003).
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