Study finds huge losses in the northeast
York University
Climate change and an
increase in disturbed bee habitats from expanding agriculture and development
in northeastern North America over the last 30 years are likely responsible for
a 94 per cent loss of plant-pollinator networks, researchers found.
The paper, “Wild bee declines linked
to plant-pollinator network changes and plant species introductions,”
was published in the journal Insect Conservation and
Diversity.
Sandra
Rehan, an associate
professor in York University's Faculty of Science, and grad student Minna Mathiasson of the
University of New Hampshire, looked at plant-pollinator networks from 125 years
ago through present day. The networks are comprised of wild bees and the native
plants they historically rely on, although most of those have now been
disrupted.
About 30 per cent of
plant-pollinator networks were completely lost, which translates to a
disappearance of either the bees, the plants or both. In another 64 per cent of
the network loss, the wild bees, such as sweat or miner bees, or native plants,
such as sumac and willow, are still present in the eco-system, but the bees no
longer visit those plants; the association is gone.
The remaining six per cent of the plant-pollinator networks are stable or even thriving with pollinators such as small carpenter bees, which like broken stems for nest making.
“There are several
reasons for the losses in the networks," Rehan explained. "Climate
change is likely the biggest driver. We know that over the last 100 years or so
annual temperatures have changed by two and a half degrees. This is enough to alter
the time when certain native plants bloom.
“For a bee that’s out
for months on end or is a generalist pollinator, this isn’t such a critical
mismatch, but for a bee that’s only out for two weeks of the year and only has
a few floral hosts, this could be devastating.”
An increase in
non-native species of bees and invasive species of plants, which have displaced
some of the native species, is another reason for the decline in networks.
“We are getting a lot
of invasive species and new records of invasive species every year. This is
usually accidentally through trade and through ornamental plants,” said Rehan.
A lot of these bees
live in stems, so it’s easy to import plants along with non-native bee species
without knowing it. “We can actually show routes and means of invasion
biology,” she continued.
These bees are
following shipping routes from one continent to the other around the world,
including to North America through ornamental plants for our gardens.
The researchers say an
increase in habitat restoration and native flowering plants in agricultural
landscapes are critical for improving wild bee biodiversity, but also food
security for humans.
Bees and other
pollinators generate hundreds of billions of dollars of economic activity
globally by pollinating crops, and wild bees are at the top of the list
believed to pollinate more than 87 per cent or 308,006 flowering plant species.
Many of these are economically important commercial crops, such as apples and
blueberries.
“There is an urgent
need to gain a deeper understanding of the environmental circumstances
affecting these wild pollinator populations and their specialized, evolutionary
relationships with plant communities,” said Rehan. “Plant pollinator webs are
dependent on changes in the landscape, so knowing how these networks are shaped
is important for all regional habitats.”
Recent research by
Rehan and her team looked at 119 wild bee species over 125 years and found 14
declining and eight increasing species. All of the wild bee species in decline
are native and over half experienced significant range latitude and elevation
shifts.
