Flexible diets enable pollinators to cope with changes in plant community composition

Switching plant species visited by pollinators (partner flexibility), has
been proposed as a behavioural mechanism able to attenuate the negative
impacts of shifts in plant communities on pollination. However, it is
unclear if the magnitude of such response is generalizable or depends on
the environmental context. Moreover, the ability of pollinators to exploit
plants with dissimilar traits (trait flexibility) has been overlooked,
even though it can affect the spectrum of new partners available. To shed
some light on this problem, we quantified partner and trait flexibility in
five communities from four different environments, from Alpine to
semi-arid. We evaluated if the rate at which pollinators incorporated new
plant species throughout the flowering season was similar across
communities or context-dependent. Then, we assessed if pollinators changed
the type of flowers visited and if such trait flexibility was related to
their capacity to visit new plant species. Finally, we developed an
agent-based model to explore if diet flexibility can protect pollination
when the plant community changes. To this end, we used scenarios of
phenological decoupling. In general, pollinators switched interaction
partners to cope with the temporal replacement of plant species. Yet, the
magnitude of such behaviour varied across communities, probably in
response to differences in the number of floral resources available. Also,
pollinators were able to visit plant species with dissimilar traits,
though both components of diet flexibility (partner identity and traits)
did not necessarily covary. Thus, to have a full picture of pollinators’
diet flexibility we need to consider the floral traits of partners.
Finally, our theoretical model shows that diet flexibility can protect
pollination after shifts in plant communities; but that such positive
effects are limited by trait-matching between co-occurring species.
Overall, our study highlights the importance of incorporating plant traits
when evaluating the ability of pollinators to find new interaction
partners. Besides, our simulation results suggest that diet flexibility
may not unequivocally protect pollination against changes in plant
communities, especially if they entail shifts in the characteristics of
the floral assemblage, and hence, the ability of pollinators to find new
interaction partners can be compromised.