Humming along or buzzing off? The elusive consequences of plant-pollinator mismatches

Temporal mismatches among plants and pollinators, driven by climate change, are considered a potential cause of population declines of these mutualists. However, field studies demonstrating population declines as a result of climate-driven phenological mismatches are uncommon, and the extent to which mismatches will be a problem in the future remains unclear. We revisit predicted consequences of climate-driven phenological mismatch in plant-pollinator systems by identifying nine previously-applied assumptions that are violated or insufficiently understood in real systems. Briefly, the assumptions are: (1) Dates of first-flowering (DFF) or dates of first activity (DFA) correctly describe phenology, and disparities between DFF and DFA represent the magnitude of mismatch. (2) “Optimal” matches are measured correctly. (3) Advancement of DFF or DFA will be the primary phenological change in the future. (4) Future phenological shifts will be independent for each species. (5) All plant-pollinator interactions are equally effective. (6) Populations of plants and pollinators are limited by mutualistic interactions. Some previous models have also assumed that the effects of future mismatches will not be influenced by (7) emergence of novel interactions, (8) competition or facilitation from altered co-flowering and co-flight, and (9) phenotypic plasticity and rapid adaptive evolution of phenology. Those assumptions affect the direction, extent, and accuracy of predicted consequences of future phenological mismatch. In discussing them, we identify important topics for future research in pollination ecology