The definitions of ecosystem function (EF) in the literature can be ‘dense’ and confusing. Four key example are given below.
- De Groot (1992) defined ecosystem function as ‘the capacity of natural processes and components to provide goods and services that satisfy human needs, directly or indirectly’. EF is therefore, ‘a subset of ecological processes and ecosystem structures’ (De Groot et al. 2002). Ideas about what constitutes an ecosystem function have evolved since 1992. The above De Groot et al. definition can now be seen as confusing EF with ecosystem services (ES), as it includes ‘goods and services’.
- Costanza et al. (1997) defined EF as the habitat, biological or systems properties or processes of ecosystems. In other words, it describes the internal functioning of ecosystems such as the interactions between the abiotic and biotic components (vegetation, water, soil, atmosphere and biota) that transfer energy and matter within and across ecosystems. This is a generally accepted definition of EF. When value to mankind, usually expressed in financial terms but also including spiritual, artistic and wellbeing benefits, is considered, it becomes an ES.
- Hooper et al. (2005) defined EF as a ‘broad term that encompasses a variety of phenomena, including ecosystem properties, ecosystem goods, and ecosystem services’. Although published eight years after Costanza et al. (1997), this paper defined EF to include ‘goods and services’. In terms of current paradigms, this can now be seen as confusing EF with ES.
- Naeem (2009) also defined EF as the biogeochemical (i.e., geochemical processes influenced by biological processes) activities of ecosystems. This definition focuses on ‘activity’ and identifies primary production as one of the most important ecosystem functions, although by implying a ranking in this way EF does imbue the definition with value, again invoking ES.
For the purposes of the current work, the definition of EF by Costanza et al. (1997) will be used. EF are important because they maintain ecosystems and biodiversity. Some of these functions may directly or indirectly provide goods (e.g., food) and services (e.g., waste assimilation) that benefits’ mankind (i.e., ES). In such instances, a single EF may produce two or more ES, or multiple EFs may be needed to produce a single ES (Costanza et al. 1997). However, not all EF lead to ES.
EF is an outcome of one or more EPs. Table 2 shows how combinations of ecosystem processes result in ecosystem functions and how these can lead to some ecosystem services (Costanza et al. 1997; Wall and Virginia 2000; De Groot et al. 2002).
Table 2 The relationship between ecosystem processes, ecosystem functions and services: some examples
|Photosynthesis and plant nutrient uptake
||Primary production-see photograph below
||Food and energy (e.g., fuel, food, organic matter), fodder (e.g., leaves, litter)|
|Population reduction of hervibores through trophic-dynamic relations
||Predation and parasitism-see video below
||Control of pests and diseases, reduction in crop damage|
|Storage and re-cycling of nutrients by living organisms
||Maintains healthy soil and productive ecosystems|
|Biogeochemical cycles in ecosystems (e.g., CO2/O2 balance, ozone layer etc.)
||UV-B protection by O3, maintains air quality|
|Mineral weathering, soil bioturbation, plant colonisation and accumulation of organic matter
||Maintains the productivity of agricultural lands and natural productive soils|
Examples of ecosystem functions:
Parasitism: Aphelinus abdominalis Dalman stinging the distal abdominal area of an aphid. Video: Eric Wyss with permission.
Transpiration: Scanning electron micrograph of lilac leaf stomata (Syringa vulgaris L.). Photo: http://www.psmicrographs.co.uk/
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De Groot, R, 1992. Functions of Nature: Evaluation of Nature in Environmental Planning, Management and Decision Making. Wolters-Noordhoff, Groningen.
De Groot R, Wilson M, Boumans R, 2002. A typology for the classification, description and valuation of ecosystem functions, goods and services. Ecological Economics 41: 393-408.
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Naeem S, Wright P, 2003. Disentangling biodiversity effects on ecosystem functioning: deriving solutions to a seemingly insurmountable problem. Ecology Letters 6: 567–579.