Th e structure of species interaction networks is important for species coexistence, community stability and exposure of species to extinctions. Two widespread structures in ecological networks are modularity, i.e. weakly connected... more
Th e structure of species interaction networks is important for species coexistence, community stability and exposure of
species to extinctions. Two widespread structures in ecological networks are modularity, i.e. weakly connected subgroups of
species that are internally highly interlinked, and nestedness, i.e. specialist species that interact with a subset of those species
with which generalist species also interact. Modularity and nestedness are often interpreted as evolutionary ecological
structures that may have relevance for community persistence and resilience against perturbations, such as climate-change.
Th erefore, historical climatic fl uctuations could infl uence modularity and nestedness, but this possibility remains untested.
Th is lack of research is in sharp contrast to the considerable eff orts to disentangle the role of historical climate-change
and contemporary climate on species distributions, richness and community composition patterns. Here, we use a global
database of pollination networks to show that historical climate-change is at least as important as contemporary climate
in shaping modularity and nestedness of pollination networks. Specifi cally, on the mainland we found a relatively strong
negative association between Quaternary climate-change and modularity, whereas nestedness was most prominent in areas
having experienced high Quaternary climate-change. On islands, Quaternary climate-change had weak eff ects on modularity
and no eff ects on nestedness. Hence, for both modularity and nestedness, historical climate-change has left imprints
on the network structure of mainland communities, but had comparably little eff ect on island communities. Our fi ndings
highlight a need to integrate historical climate fl uctuations into eco-evolutionary hypotheses of network structures, such
as modularity and nestedness, and then test these against empirical data. We propose that historical climate-change may
have left imprints in the structural organisation of species interactions in an array of systems important for maintaining
biological diversity.
species to extinctions. Two widespread structures in ecological networks are modularity, i.e. weakly connected subgroups of
species that are internally highly interlinked, and nestedness, i.e. specialist species that interact with a subset of those species
with which generalist species also interact. Modularity and nestedness are often interpreted as evolutionary ecological
structures that may have relevance for community persistence and resilience against perturbations, such as climate-change.
Th erefore, historical climatic fl uctuations could infl uence modularity and nestedness, but this possibility remains untested.
Th is lack of research is in sharp contrast to the considerable eff orts to disentangle the role of historical climate-change
and contemporary climate on species distributions, richness and community composition patterns. Here, we use a global
database of pollination networks to show that historical climate-change is at least as important as contemporary climate
in shaping modularity and nestedness of pollination networks. Specifi cally, on the mainland we found a relatively strong
negative association between Quaternary climate-change and modularity, whereas nestedness was most prominent in areas
having experienced high Quaternary climate-change. On islands, Quaternary climate-change had weak eff ects on modularity
and no eff ects on nestedness. Hence, for both modularity and nestedness, historical climate-change has left imprints
on the network structure of mainland communities, but had comparably little eff ect on island communities. Our fi ndings
highlight a need to integrate historical climate fl uctuations into eco-evolutionary hypotheses of network structures, such
as modularity and nestedness, and then test these against empirical data. We propose that historical climate-change may
have left imprints in the structural organisation of species interactions in an array of systems important for maintaining
biological diversity.
