Editing Ecosystem (section)

===Function and biodiversity===
{{Main|Biodiversity}}{{See also|Ecosystem diversity}}
[[File:View of loch lomond.JPG|thumb|[[Loch Lomond]] in [[Scotland]] forms a relatively isolated ecosystem. The fish community of this lake has remained stable over a long period until a number of [[introduced species|introductions]] in the 1970s restructured its [[food web]].<ref>{{cite journal | last=Adams | first=C.E. | title=The fish community of Loch Lomond, Scotland: its history and rapidly changing status | journal=Hydrobiologia | year=1994 | volume=290 | issue=1–3 | pages=91–102 | doi=10.1007/BF00008956 | s2cid=6894397 | doi-access=free | bibcode=1994HyBio.290...91A }}</ref>]]
[[File:Spiny Forest Ifaty Madagascar.jpg|thumb|Spiny forest at Ifaty, [[Madagascar]], featuring various ''[[Adansonia]]'' (baobab) species, ''[[Alluaudia procera]]'' (Madagascar ocotillo) and other vegetation]]
[[Biodiversity]] plays an important role in ecosystem functioning.<ref name="Schulze-2005">{{cite book |last=Schulze |first=Ernst-Detlef |author2=Erwin Beck |author3=Klaus Müller-Hohenstein  |title=Plant Ecology |publisher=Springer |location=Berlin |year=2005 |isbn=978-3-540-20833-4}}</ref>{{rp|449–453}} Ecosystem processes are driven by the species in an ecosystem, the nature of the individual species, and the relative abundance of organisms among these species. Ecosystem processes are the net effect of the actions of individual organisms as they interact with their environment. [[Theoretical ecology|Ecological theory]] suggests that in order to coexist, species must have some level of [[limiting similarity]]—they must be different from one another in some fundamental way, otherwise, one species would [[competitive exclusion|competitively exclude]] the other.<ref name="Schoener-2009">{{cite book|last=Schoener|first=Thomas W.|title=The Princeton Guide to Ecology|url=https://archive.org/details/princetonguideto00levi|url-access=limited|editor=Simon A. Levin|editor-link=Simon A. Levin|publisher=Princeton University Press|location=Princeton|year=2009|pages=[https://archive.org/details/princetonguideto00levi/page/n16 2]–13|chapter=Ecological Niche|isbn=978-0-691-12839-9}}</ref> Despite this, the cumulative effect of additional species in an ecosystem is not linear: additional species may enhance nitrogen retention, for example. However, beyond some level of species richness,<ref name="Chapin-2011j" />{{rp|331}} additional species may have little additive effect unless they differ substantially from species already present.<ref name="Chapin-2011j" />{{rp|324}} This is the case for example for [[Introduced species|exotic species]].<ref name="Chapin-2011j" />{{rp|321}}

The addition (or loss) of species that are ecologically similar to those already present in an ecosystem tends to only have a small effect on ecosystem function. Ecologically distinct species, on the other hand, have a much larger effect. Similarly, dominant species have a large effect on ecosystem function, while rare species tend to have a small effect. [[Keystone species]] tend to have an effect on ecosystem function that is disproportionate to their abundance in an ecosystem.<ref name="Chapin-2011j" />{{rp|324}}

An [[ecosystem engineer]] is any [[organism]] that creates, significantly modifies, maintains or destroys a [[Habitat (ecology)|habitat]].<ref>{{Cite journal|last1=Jones|first1=Clive G.|last2=Lawton|first2=John H.|last3=Shachak|first3=Moshe|date=1994|title=Organisms as Ecosystem Engineers|journal=Oikos|volume=69|issue=3|pages=373–386|doi=10.2307/3545850|issn=0030-1299|jstor=3545850|bibcode=1994Oikos..69..373J }}</ref>