Climate change creates an evolutionary mismatch between bees and flowers

Climate change is wreaking havoc on bumblebees and flowers in the Colorado mountains, with a study comparing 40 years of records showing steep decreases in the number of both.

But it’s also had another surprising, rather more complex effect. It has caused a rapid evolution by the bees, which are outpacing the flowers in adapting to the new conditions.

Too much heat can reduce flowering of mountain plants and this is where global warming is having its affect.

Wired has the details:

On one of the mountains in the study, between 1960 to 1985 only 12 percent of the years were hot enough to reduce flowering. Since 1985, 48 percent percent of years were too hot for flowers that bumblebees typically forage on.
Since 1970, the total number of flowers available for bees on the mountain study sites declined by 60 percent overall.

That’s having a big affect on the bees which, between 1966 and 1980, were mostly “long-tongued” bees, designed to specialise in narrow tubular flowers, to both bee’s and flower’s benefit.

Since 2012, though, long-tongued bees have declined by nearly a quarter as fewer flowers force the bees to become less selective. But the speed at which the population has changed has astounded scientists.

What no one expected was that the tongues of long-tongued bees would get shorter. A lot shorter. “A 24 percent decrease in tongue length is really dramatic,” says Miller-Struttmann. “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.” Bumble bee bodies also got slightly smaller, but not as much as the tongues shrank. The research team did not find changes in the depth of the flowers bumble bees were visiting. The bees’ shape changed, but the flowers didn’t.

But the flowering plants are much longer-lived than the bees and their generation time is in the decades not a single year and so the bumblebees and plants, that have traditionally been co-evolutionary, are now 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 they’re much longer-lived species. Their generation time is decades, not yearly. Change will be slower—or may not happen at all.

The full paper can be found here: Miller-Struttmann, et al. 2015. Functional mismatch in a bumble bee pollination mutualism under climate change.