Novel ecosystems and the role of non-native species in providing ecosystem services

Background/Question/Methods

Non-native species are a pervasive component of global change, often interrupting ecosystem services upon which humans depend; falling water tables in South Africa, clogged drains in the Great Lakes, endemic species extinctions, and widespread timber and crop diseases are key examples.  However, as I review here, non-native species also provide ecosystem services throughout the biosphere, specifically in (1) lands used for agriculture or built over, and (2) novel ecosystems—those that differ in abiotic and biotic properties from ecosystems that prevailed historically, but are not actively used.  

Results/Conclusions

In the portion of the biosphere directly used by humans, non-native species provide food and timber, accounting for a clear majority of all crop production worldwide.  Within used lands, non-native species are also employed to control pests and diseases through biocontrol, stabilize soil in reclamation efforts, and provide cultural, aesthetic, and recreational benefits, particularly in urban landscapes.  In areas not actively used, novel ecosystems can be largely or even entirely dominated by non-native species, and in these systems non-native species drive the ecosystem processes that act as the supporting services of nature (i.e., primary productivity, carbon sequestration, nutrient cycling, pollination, dispersal, among others).  However, influence by non-native species does not imply loss of ecosystem services; changes may be negative, neutral, or positive, and they may occur at the expense of native species that previously provided these services, or promote their abundance.  A large number of native species are now dependent on non-native species for habitat, pollination, or dispersal, including some endangered species.  Non-native species in novel ecosystems also have the potential to provide services that were not possible with the native flora or fauna; non-native mangroves filter sediment, guard corals, and provide fish habitat where these species were not previously found.  Finally, the mechanisms by which species influence ecosystem processes (and thereby ecosystem services) appear to be consistent between native and non-native species: experimental and observational studies suggest that biological diversity maintains ecosystem processes at small spatial scales in novel ecosystems, as has been widely shown for ecosystems dominated by native species.  Ultimately, insofar as humans value the services of nature, the fact that they are provided by non-native species should not impugn their value.