Aim Extinctions and coextinctions seriously threaten global plant–pollinator assemblies, and thus a better understanding of the geographic variability in their robustness is urgently required. Although the geographic patterns of species extinction rates are frequently explored, it remains largely unknown how the subsequent coextinction risk of species varies across environments. We hypothesize that the geographic variation of network robustness to extinctions is mediated by modularity – the tendency of a network to be organized in modules of strongly interacting species – because modularity buffers perturbations and varies across environments. Location Global. Time period Current. Major taxa studied Flowering plants and their animal pollinators. Methods Using 79 pollination networks, we first explored the variation of network robustness across geographic and climatic gradients and, second, analysed the role of modularity in explaining the association between robustness and those environmental gradients. We quantified the robustness of taxonomic, functional and phylogenetic diversity of pollinators under simulated coextinctions triggered by specialist‐first, generalist‐first, and random plant removals. Results Only the robustness of phylogenetic diversity under specialist‐first removals showed a global latitudinal trend by which robustness increased towards the tropics on mainlands but increased towards the poles on islands. Generally, robustness was strongly promoted by modularity, and also directly dampened by insularity and precipitation seasonality (PS). Through the mediation of modularity, robustness was indirectly increased by actual evapotranspiration and PS, and decreased by the interaction between PS and insularity. Besides, network size and sampling area affected robustness but did not influence modularity. Main conclusions The indirect environmental effect on robustness via modularity was prevalent, which supports our hypothesis and reveals the importance of network structure in mediating the geographic variation of network robustness. The global pattern of robustness indicates the phylogenetic diversity of pollinators is relatively vulnerable to the loss of specialist plants in tropical islands and high‐latitude mainland compared to other regions.
Species interactions have evolved from antagonistic to mutualistic and back several times throughout life’s history. Yet, it is unclear how changes in the type of interaction between species alter the coevolutionary dynamics of entire communities. This is a pressing matter, as transitions from mutualisms to antagonisms may be becoming more common with human-induced global change. Here, we combine network and evolutionary theory to simulate how shifts in interaction types alter the coevolution of empirical communities. We show that as mutualistic networks shift to antagonistic, selection imposed by direct partners begins to outweigh that imposed by indirect partners. This weakening of indirect effects is associated with communities losing their tight integration of traits and increasing their rate of adaptation. The above changes are more pronounced when specialist consumers are the first species to switch to antagonism. A shift in the outcome of species’ interactions may therefore reverberate across communities and alter the direction and speed of coevolution.
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