Editing IPCC:AR6/WGII/Chapter-2 (section)

===== 2.4.2.3.3 Emergence of novel communities and invasive species =====

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As climate change is increasing the movements of species into new areas, there is concern about how exotic species are being impacted, either by becoming invasive or by already invasive species gaining even more advantage over native species. Modelling predicts that the effects of climate warming on food web structure and stability favour the success of invading species ( [[#Sentis--2021|Sentis et al., 2021]] ). Both simulated warming experiments ( [[#Zettlemoyer--2019|Zettlemoyer et al., 2019]] ) and long-term observations ( [[#Willis--2010|Willis et al., 2010]] ) have found phenologies of exotic species to respond more adaptively to warming than those of natives; in the long-term observations, the success of exotics was attributed to their greater phenological responsiveness. In an expert assessment of the future relative importance of different drivers of the impacts of biological invasions, climate change was named as the most important driver in polar regions, second-most important in temperate regions (after trade/transport), and third-most important in the tropics (after trade/transport and human demography/migration) ( [[#Essl--2020|Essl et al., 2020]] ).

However, not all exotic species become invasive. As novel climate conditions develop, novel communities made up of new combinations of species are emerging as populations and species adapt and shift their ranges differentially, not always with negative consequences ( ''high confidence'' ) ( [[#Dornelas--2014|Dornelas et al., 2014]] ; [[#Evers--2018|Evers et al., 2018]] ; [[#Teixeira--2020|Teixeira and Fernandes, 2020]] ). Novel communities differ in composition, structure, function and evolutionary trajectories, as the proportions of specialists and generalists, native, introduced and range-shifting species change and species interactions are altered, ultimately affecting ecosystem dynamics and functioning ( [[#Lurgi--2012|Lurgi et al., 2012]] ; [[#Hobbs--2014|Hobbs et al., 2014]] ; [[#Heger--2019|Heger and van Andel, 2019]] ). The exact nature of novel communities is difficult to predict because species-level uncertainties propagate at the community level due to ecological interactions ( [[#Williams--2007|Williams and Jackson, 2007]] ). However, observations, experimental mesocosms ( [[#Bastazini--2021|Bastazini et al., 2021]] ), and theoretical models ( [[#Lurgi--2012|Lurgi et al., 2012]] ; [[#Sentis--2021|Sentis et al., 2021]] ) provide support that novel communities will continue to emerge with climate change ''(medium confidence)'' .

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