Global warming may cause bees to mistime Spring emergence, missing their food supply

6 July 2017 (Yale Environment 360) – If it’s all in the timing, then climate change may spell problems for bees. Scientists have found that global warming may cause temporal mismatches between bees and the plant species on which they depend for food.German researchers from the University of Würzburg, reporting in the Journal of Animal Biology, investigated three different species of bees that hatch in the spring. They set up 36 flight cages, which allowed them to time the emergence of the bees so it was simultaneous with the flowering of plants in the cage or occurred three or six days prior to flowering. The study showed that bees that hatched prior to flowering suffered from lower rates of reproduction, were less active, and faced greater risk from predators and parasites.“Already a minor temporal mismatch of three or six days is enough to harm the bees,” says Mariela Schenk, the study’s author.The decline of bee species, adds ecologist Andrea Holzschuh, who led the study, would also reduce plant pollination in general, which is widely viewed as a threat to global agriculture.

Global Warming May Cause Bees to Mistime Spring Emergence, Missing Their Food Supply

ABSTRACT:

Global warming can disrupt mutualistic interactions between solitary bees and plants when increasing temperature differentially changes the timing of interacting partners. One possible scenario is for insect phenology to advance more rapidly than plant phenology.
However, empirical evidence for fitness consequences due to temporal mismatches is lacking for pollinators and it remains unknown if bees have developed strategies to mitigate fitness losses following temporal mismatches.
We tested the effect of temporal mismatches on the fitness of three spring-emerging solitary bee species, including one pollen specialist. Using flight cages, we simulated (i) a perfect synchronization (from a bee perspective): bees and flowers occur simultaneously, (ii) a mismatch of 3 days and (iii) a mismatch of 6 days, with bees occurring earlier than flowers in the latter two cases.
A mismatch of 6 days caused severe fitness losses in all three bee species, as few bees survived without flowers. Females showed strongly reduced activity and reproductive output compared to synchronized bees. Fitness consequences of a 3-day mismatch were species-specific. Both the early-spring species Osmia cornuta and the mid-spring species Osmia bicornis produced the same number of brood cells after a mismatch of 3 days as under perfect synchronization. However, O. cornuta decreased the number of female offspring, whereas O. bicornis spread the brood cells over fewer nests, which may increase offspring mortality, e.g. due to parasitoids. The late-spring specialist Osmia brevicornis produced fewer brood cells even after a mismatch of 3 days. Additionally, our results suggest that fitness losses after temporal mismatches are higher during warm than cold springs, as the naturally occurring temperature variability revealed that warm temperatures during starvation decreased the survival rate of O. bicornis.
We conclude that short temporal mismatches can cause clear fitness losses in solitary bees. Although our results suggest that bees have evolved species-specific strategies to mitigate fitness losses after temporal mismatches, the bees were not able to completely compensate for impacts on their fitness after temporal mismatches with their food resources.