Over the last half-decade, nearly a third of the North American bee
population has disappeared. New research suggests in some parts of the
United States, climate change could be the reason bee populations
continue to shrink.
To better understand how global warming affects bee health,
scientists from Northwestern University and the Chicago Botanic Garden exposed bee nests in Arizona to a variety of temperatures. Researchers altered the temperatures by painting the nests black, white and clear.
Black paint caused the nests to absorb more of the sun's energy,
replicating the region's future climate, should temperatures continue to
rise unabated. The black paint effectively fast-forwarded to the
climate of the years 2040 to 2099.
White paint caused the hives to reflect heat, taking bees back in
time to climate conditions similar to those observed in the 1950s. Clear
paint worked as a control.
"It's pretty low-tech, but it works," Northwestern researcher Paul
CaraDonna said in a news release. "The field site is so remote that
something more high-tech with solar panels or a power source was out of
the question."
The study included 90 nests in Arizona's Santa Catalina Mountains, an
area where bees continue to thrive. All of the nests were inhabited by a
native species known as the mason bee, Osmia ribifloris, also called the blueberry mason bee.
Scientists replicated the experiment twice, observing back-to-back
seasons. Each season, researchers found bees in the black nests suffered
increased mortality rates and emerged early from diapause over a longer
period of time. Diapause is a term to describe insect hibernation.
Normally, bees wake up from diapause over the course of 10 to 15
days, but bees developing and hibernating under warmer conditions
emerged from diapause over a 50-day period.
"This suggests that they are responding to a stressful environment,"
CaraDonna said. "Because their emergence times are altered, they now
potentially have fewer floral resources available to them as a
population, and it might be a lot harder to find mates."
Bees emerging from black nests were also smaller and had lower levels
of body fat. Scientists hypothesized warmer temperatures accelerated
the bees metabolism during diapause.
"For insects, size is a big deal," CaraDonna said. "Bigger is usually
better. It means you have greater energy stores, which essentially
means you can weather more storms. As a bee, that means you are likely
able to reproduce more, which has implications for the stability of the
population."
According to the new study -- published this week in the journal Functional Ecology -- climate change may begin to push some bee species up against their physiological limits.
It's likely the bee populations will move to higher elevations as
temperatures continue to warm, but the migration would leave native
manzanita plants without their usual pollinator.
"This mason bee is probably one of the best pollinators for this
plant species, so if you take away the pollinator, you might take away
the plant in the longer term," CaraDonna said. "We need to understand
how nature works and see how it responds to important sources of
variation. Otherwise, we don't have the ability to keep it safe."
When News Breaks Out, We Break In. (The 2014 Bloggies Finalist)
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