The western bumble bee is one of several bumble bees being considered for endangered species listing due to climate change effects, but also the use of pesticides, especially neonicotinoids, which attack insect nervous systems. Photo courtesy USGS BIML Team
by Laura Lundquist
The lifespan of a bee is just
40 days. This seems short, but during that time it can visit as many as 1,000
blossoms. In so doing, such a short-lived creature can secure the longevity of
many a flowering species simply by ferrying pollen from one flower to the next.
Multiply that by millions of bees and you have the makings of a diverse
ecosystem.
But there are an increasing
number of manmade threats can cut a bee’s life even shorter or worse, abort it
from the start. The death of one bee might not cause too much concern, but when
entire populations are affected along with other pollinators like butterflies,
it can have devastating implications for the 87 percent of flowering plants
that depend on animal pollination.
Over the past couple decades,
scientists have been uncovering the extent of pollinator decline. The
Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem
Services estimates 40 percent of insect pollinators are at risk of extinction
worldwide. In North America, the relative abundance of several bumble
bee species has dropped by up to 96 percent.
Several factors are
contributing to these declines, including land-use changes, pesticide use,
pathogens, competition with managed bees, and climate change. Knowing that time
and resources are limited, two scientists recently reviewed all the related
research to find which is the most detrimental for pollinators. Not
surprisingly, it’s the factor that is the hardest to stop: climate change.
In mid-May, the journal Commonwealth Agricultural Bureau
International Reviewspublished the findings of Wisconsin researcher Johanne Brunet,
who had scoured more than 150 journal articles related to worldwide pollinator
decline. She concluded that to save pollinators, a more holistic approach is
needed, one where natural habitat is integrated with agricultural lands that
are treated with less pesticide. But because climate change poses the greatest threat to pollinators, nations across
the globe must do more to reduce greenhouse gases.
“Climate change has the most
diverse negative impacts on pollinators and is the threat most difficult to
control,” Brunet said in a May 15 release. “However, its consequences threaten
food security and world stability, thus efforts to control it must be
prioritized at a global scale.”
In the realm of research,
insects have often been overlooked unless a specific bug jeopardizes a valuable
crop, such as the mountain pine beetle which threatens various timber species.
Plus, insects can be difficult to study since many are hard to find and
sampling methods can be lethal. Over the past few decades, however, issues such
as honeybee colony collapse have prompted scientists to start investigating the
20,000 bee species that exist worldwide, 85 percent of which live solitary
lives instead of clustering in hives.
The Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services estimates 40 percent of insect pollinators are at risk of extinction worldwide.
Researchers studied how
pollinators would react in general to overall climate trends using models that
predict increasing worldwide average temperatures and drought in some areas,
and higher rainfall in others. The changes in water and temperature are
predicted to affect plants and their pollinators, particularly in specialized
systems where one species depends primarily on another, such as milkweed and
monarch butterflies.
Drought and higher
temperatures caused by a warming climate, for example, can decrease the size or
the number of flowers a plant produces and can even change a flower’s scent.
These alterations could make it more difficult for pollinators to locate
flowers. Also, drought or heat would tend to cause the few small blossoms that
remain to produce less nectar and pollen, so a bee or butterfly would receive
less of a reward. Both trends need further research to determine any effect on
pollinators, Brunet said.
Schematic representation of drivers of pollinator decline. Graphic courtesy CABI Reviews
Scientists have also
predicted that higher temperatures can alter the time of year when pollinators
emerge and when plants begin to flower. That could cause problems if
pollinators appear before flowers begin to bloom or vice versa, but so far that
scenario not been documented.
Colorado State University
graduate student Kathleen Whipple tried to find such a disconnect in the
pollinators and flowers of Yellowstone National Park. She chose the park for
her study site partly because it’s free from most other threats to pollinators,
so any observed shift could be credited to climate change. It also meant she
could take advantage of several decades of data that her advisor, Gillian
Bowser, has gathered in the park.
In the 1980s, when Bowser was
searching for a graduate project, National Park Service biologist Mary Meagher
suggested that Bowser investigate Yellowstone’s pollinators, most if not all of
which were unknown at the time. Taking the advice, Bowser researched
butterflies and plants in the Cougar Creek area of the park and has repeatedly
returned to document 400 species of butterflies.
With each successive visit,
Bowser and Whipple have seen changes in Cougar Creek, including faster snowmelt
and earlier flower blooms. Whipple noted in her 2023 dissertation that flowers
are now blooming on average three days earlier than in the 1980s, but that
shift is still too small to see any resulting divergence between flower
availability and pollinator visits.
In North America, the relative abundance of several bumble bee species has dropped by up to 96 percent.
While Yellowstone provides an
almost unsullied ecosystem for such study, it has one aspect that can obscure
the effects of climate change: its mountains and the elevational gradient they
offer. For example, while the mid-elevation Cougar Creek meadow has seen a
three-day shift in flower onset, the shift in the subalpine plants occurs five
days earlier at higher elevations where warming has a greater effect. But
pollinators can fly up or down to wherever flowers might be blooming, so any
lack of synchrony is blurred.
Whipple concluded, “the
climate in the GYE has changed, but pollinator and floral species responses to
such change are less clear.” Again, she said, more research is needed.
“Understanding these shifts
is so important for us to protect pollinators in the long run because they’re
little, tiny guys. They’re hard to see sometimes, but they perform such a
critical service for us in terms of our food crops and agricultural systems as
well as the preservation of our national parks, yet we pay very little
attention to what’s happening to them regarding climate change,” Bowser said in a CSU release.
However, the direct effect of
heat on pollinators is very clear and very scary. Brunet’s review shows that
larval and adult insects, like most animals, are more likely to die in high
heat. Either that or they move away, escaping to higher elevations or farther
north, causing localized extinction. That’s particularly devastating in those
specialized systems where a plant species could be left without its pollinator.
That plant dies out too.
An anise swallowtail butterfly perches on a pine in Yellowstone National Park. Yellowstone is home to 134 species of butterfly. Photo courtesy NPS
Last year, the U.S. Fish and
Wildlife Service published a study that found increasing temperature,
particularly the extended heat waves that have increasingly settled over the
Northern Rocky Mountains, have a devastating effect on larger bees, including
the western bumble bee, which is most abundant in Greater Yellowstone but has seen a 57 percent decline in its historical range, according to the study.
“Even considering the most
optimistic scenario, western bumble bee populations are expected to continue to
decline in the near future in nearly half of the regions across the bumble
bee’s range,” said USGS scientist Tabitha Graves said in a
January 2023 release.
“Considering the more severe, but probably more likely scenarios, western
bumble bee populations are expected to decline an additional 51 percent to 97
percent from 2020 levels depending on the region.”
The western
bumble bee is one of several bumble bees being considered for endangered
species listing due to climate change effects, but also the use of pesticides,
especially neonicotinoids, which attack insect nervous systems. Western bumble
bees have been documented visiting huckleberry, snowberry and penstemon flowers
among others, so their extinction could noticeably change the vegetation of the
West.
For most threats that
pollinators face, Brunet identified several solutions. When it comes to
pesticides and other chemicals, people can reduce their effect by using fewer
toxic chemicals and spraying at night when pollinators aren’t active. Human
development of wild lands poses a major threat because it eliminates food
sources and nesting spots, and forces pollinators to fly greater distances to
find flowers as habitat becomes more fragmented. In
these developed areas, people can improve conditions by planting native flower
gardens and by maintaining wild habitat around agricultural fields, Brunet said.
But when it comes to the
changing climate, no immediate solutions exist to help pollinators. That’s all the more
reason to eliminate what threats we can.
“Climate change is the most
critical threat to pollinators, and research must continue to study its impacts
and develop solutions,” Brunet concluded in the review. “Public education on the negative impacts of climate
change on plants and their pollinators and the implications for human diet and
lives must take place at a global scale. Climate change is a global problem and
a political one with strong implications for food security and world
stability.”
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About Laura Lundquist
Laura Lundquist earned a journalism degree from the University of Montana in 2010, and has since covered the environmental beat for newspapers in Twin Falls, Idaho and Bozeman, in addition to a year of court reporting in Hamilton. She's now a freelance environmental reporter with the Missoula Current Online Journal.