Since the 1960s, the tongue length of two alpine bumblebee species in the Rocky Mountains has decreased by about 25 percent. That is the result of a recent study of a US research team. “So what?” one might be inclined to ask. But the conclusions of the researchers reveal a fascinating story of how nature addresses the climate change challenge.
In the 1960s, long-tongued bumblebees and flowers with deep corolla tubes, made wonderful partners. The bees provided reliable pollination services and in return had monopoly access to a stable source of nectar hidden deep at the bottom of the flower. Then came the warmer summers, and the alpine flora reacted by reducing flowering. Since 1970, the total number of flowers available for bees on the mountain study sites declined by 60 percent overall.
The long-tongued bumble bees reacted to the scarcity of their favorite flowers by becoming less selective. The range of plants they foraged on changed significantly and included flowers with shorter nectar tubes. At the same time, warmer temperatures brought new competition for pollen and nectar: some lower altitude bees were now able to live in higher mountain elevations and moved in.
Over the years, this led to an evolutionary change: building and maneuvering a big tongue takes energy, so the tongues of the long tongued bees got shorter by a dramatic 24 percent. “That was in 40 years, in 40 generations, I should say, because these bumblebees only have one generation a year. That’s a pretty short period of time to see such a dramatic shift,” says Nicole Miller-Struttmann, lead author of the study. This rapid evolution of the pollinators suggests that it is not time to give up on mountain bumblebees just yet.
But what about the flowers?
The scientists found no evidence that the long-tubed flowers had changed. Right now bumblebees and plants they historically fed on are mismatched physiologically. The bees may not be as good a pollinator for those plants, which could cause further declines in flowers. In the long term, perhaps they will also evolve, but their generation time is decades, not yearly. So change will be slower—or may not happen at all.
However, we can help bees and plants adapt to our new warmer world by increasing areas set aside for nature, or making sure we have connections between isolated nature refuges.
The study titled “Functional mismatch in a bumble bee pollination mutualism under climate change” by Nicole E. Miller-Struttmann et al. was published in the online magazine “Science”.
It was picked up by other online media, among them by wired.com and by the Science Daily.