More flowers doesn’t mean healthier bees

In a counter-intuitive finding, researchers have discovered that longer flowering seasons due to climate change is harming rather than helping bee populations.

A team of scientists from Florida State University in the US looked at three bumblebee species native to the Rocky Mountains in Colorado. All three are native to the area’s lower altitude sub-alpine regions, where gradually warming climatic conditions have over several years induced earlier snow melts and thus longer flowering seasons.

“Knowing whether climate variation most affects bumble bees directly or indirectly will allow us to better predict how bumble bee populations will cope with continued climate change,” said Jane Ogilvie, the lead investigator. 

“We found that the abundances of all three bumble bee species were mostly affected by indirect effects of climate on flower distribution through a season.”

On the face of it, a longer flowering season would seem to offer a more abundant food supply for the insects, thereby bolstering their survival and breeding chances. The reality, however, turned out to be quite different.

The extended season, the researchers found, led to a gradual disruption of finely balanced flowering cycles for some species of plant, and, over all, led to a lowering in flower density. Total food availability at any given period, therefore, was reduced, leading to poorer food intake for the bees and reduced fitness.

“When researchers think about flower effects on bees, they typically consider floral abundance to be the most important factor, but we found that the distribution of flowers throughout a season was most important for bumble bees,” says Ogilvie. 

“The more days with good flower availability, the more bees can forage and colonies can grow, and the bigger their populations become. We now have longer flowering seasons because of earlier snow melt, but floral abundance has not changed over all. This means we have more days in a season with poor flower availability.”

Bumblebee populations are in decline across the globe due to the effects of global warming, exacerbated in many regions by the use of neonicotinoid pesticides in agriculture.

As bee colonies come under stress and their numbers decline, their critical role as pollinators for both commercial crops and wild ecosystems is also impacted.

“Declining bumble bee populations should be a warning about the expansive detrimental effects of climate change,” adds Ogilvie. 

“Bumble bees have annual life cycles, so their populations show responses to change quickly, and many species live in higher altitude and latitude areas where the change in climate is most dramatic. The effects of climate change on bumble bees should give us pause.”

The research was published in the journal Ecology Letters.