Climate change, impacts and vulnerability in Europe ... - MemoFin.fr

Climate impacts on environmental systems3.4.6 Species interactionsRelevanceThe effects of climate change on single species willhave consequences for all levels of biodiversity,ranging from the genetic level to ecosystems(Walther, 2010). These higher-level impactsare of particular importance since biodiversity,besides being realised as a value in its own right,is increasingly acknowledged as providingindispensable ecosystems services for humanwell-being (Díaz et al., 2006). Biodiversity can beregarded as 'our collective life insurance', as notedin the 'EU biodiversity strategy to 2020' (EuropeanCommission, 2011). The importance of wild speciesfor the functioning of ecosystems is manifold andlargely driven by biotic and abiotic interactions. Animproved understanding of how climate changewill affect these interactions in novel communitiesestablished under a novel climate can be utilisedto assess the extinction risk of species of particularconservation concern. It will also enhance ourabilities to assess and mitigate potential negativeeffects on ecosystem functions and services.Despite increasing knowledge about effects ofclimate change on pairwise species interactionsand on complete ecological networks, quantitativeassessments of these effects are still very uncertain.A robust conclusion from existing observational andtheoretical studies is that specialist species are atmuch higher risk from effects on species interactionsthan generalist species (Menéndez et al., 2007;Schweiger et al., 2010).Community changes triggered by climate changecan lead to disruptions or alterations of currentlyexisting species interactions and the generation ofnovel species interactions. Such changes impacton mechanisms such as competition, herbivory,predation, parasitism, pollination and symbiosisby affecting ecological matching among interactingspecies (Berg et al., 2010; Antoninka et al., 2011).These ecological matches can be defined by spatialor temporal synchronicity of occurrence (Parmesan,2006; Schweiger et al., 2008; Hegland et al., 2009;Van der Putten et al., 2010), or by energetic,morphological and behavioural demands (Corbet,2000; Schweiger et al., 2010).Climate change can also affect disturbance regimes,such as wildfires and storms. Forest fires as animportant example of such a disturbance regime arediscussed in Section 4.2.3.Past trendsDirect observations of the effects of recent climatechange on competition are scarce and are generallythought not to have led directly to the extinctionof species in Europe (Davis, 2003). However,independent studies have shown that observedchanges in the distribution and abundance ofPopulus species (a group of trees that are relativelyweak competitors) in the Late Glacial (ca. 13 000–10 000 years ago) and in the 20th century could onlybe explained when the effects of climate change onits competitors were taken into account (Peros et al.,2008; Van Bogaert et al., 2009).Climate change has already lead to temporalmismatches between species that depend on eachother for feeding and for pollination. For example,the egg hatch of the winter moth (Operophterabrumata) has advanced more than the budburst dateof its larval food plant, the pedunculate oak (Quercusrobur), over the past two decades, with potentiallysevere consequences for its fitness (Visser and Both,2005; Parmesan, 2006; van Asch and Visser, 2007;Both et al., 2009). Similarly, over the last 30 years,the occurrence of the honey bee (Apis mellifera) andthe Small White butterfly (Pieris rapae) in relationto the flowering of crucial host plants has changedKey messages: 3.4.6 Species interactions• Climate change is affecting the interaction of species that depend on each other for food or otherreasons. It can disrupt established interactions but also generate novel ones.• Negative effects on single species are often amplified by changes in interactions with other species, inparticular for specialist species.• The impact of species interactions on ecosystems services depends on whether disrupted interactionscan be buffered by system-intrinsic properties or by novel organisms.144 Climate change, impacts and vulnerability in Europe 2012