The contribution of pollination interactions to the assemblage of dry grassland communities

Temperate semi-natural dry grasslands are known for the high biodiversity they host. Several studies attempted to pinpoint principles to explain the assembly of local communities and disentangle the coexistence mechanisms that ensure the persistence of a high species richness. Similarly to habitat filtering and interspecific interactions for abiotic resources, we found that in dry grasslands interactions for pollination exert selection pressures that influence species assemblage. We found entomophilous species flowering synchrony to be a key characteristic, which may favour the long lasting maintenance of rare species populations within the community. Furthermore, plants phenological synchronization was significantly associated with the sharing of pollinator guilds. Plant species exhibited different strategies to reduce competition for pollinators and pollen loss, which included specialization on different pollinators, and temporal and spatial segregation. Aggregation of synchronous pollinator-sharing species occurred among plants diverging in the anther position. Finally, we found that the co-occurrence of different dry grassland communities at the landscape scale influenced the structure of pollination networks, by favoring the maintenance of a higher richness of pollinators, including important keystone species. However, pollinator availability was less limiting than expected for food-deceptive orchid species, which were found to be highly generalized for pollinators.