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Warming temperatures and earlier snowmelt are disrupting the long-running relationship between wildflowers and their pollinators on Colorado’s Pikes Peak.

In a new study September 25 in the American Naturalist, ���������� researchers found many of the region’s plants and pollinators are now emerging earlier in the spring than they did a century ago. But some species are falling out of sync, potentially adding challenges for pollinators already under threat. ����

“Pollinators are so important to our ecosystem, supporting everything from wildflowers to the food we eat,” said Julian Resasco, the paper’s senior author and associate professor in the Department of Ecology and Evolutionary Biology. “Having data from 100 years ago gave us a unique opportunity to take a glimpse of these long-term trends under a changing climate.”

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Pseudomasaris vespoides, a pollen wasp is showing up much earlier than it used to in the historical study. (Credit: Julian Resasco/����������)

Starting in 1910, ecologist Frederic Clements and his student Frances Long began documenting the interactions between local plants and their pollinators at the now-closed Carnegie Institution’s Alpine Laboratory on the slope of the 14,115-foot Pikes Peak near Colorado Springs.

Over the past century, Colorado has warmed by an average of 2.9°F, with the average winter temperature rising even faster, by 3.3°F. Climate change has also decreased the amount of snow accumulating on top of the mountains, or snowpack, in the western United States, reducing the amount of water available for mountain species in spring and summer.

Warming temperature and snowmelt are vital environmental cues for plants and insects to emerge from their winter inactive state.

As the climate warms and snow melts earlier, plants may begin flowering sooner and pollinators may start flying earlier. But not all species respond to it in the same way or at the same pace, said��Leana Zoller, the paper’s first author and a former postdoctoral associate at ����������.

Resasco, Zoller and their team returned to Clements and Long’s study area to see if the interactions between plants and pollinators have shifted over the past century. Because Pikes Peak is a protected wilderness area, its environment has remained largely undisturbed. This allowed the team to study the impact of climate change without other influences such as land use change.

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Julian Resasco (right) and his two graduate students surveyed pollinators and wildflowers in the Pike National Forest near Colorado Springs. (Credit: Andrew Gaier/����������)

Between 2019 and 2022, the research team analyzed 25 wild pollinator species, including bumblebees, wasps and flies, as well as 11 flowering plants the insects interact with, forming 149 pairs of interactions.

Of the species that could be compared between the historical and contemporary datasets, they found that wildflowers were blooming about 17 days sooner than a century ago, and pollinators started to fly 11 days earlier. ��

Out of the 149 pairs of plant-pollinator comparable interactions, nearly 80% have more overlap in their active periods than before. While this trend appears beneficial for pollinators now, the advantage may be short-lived.

Historically, pollinators were active earlier than plants started flowering. “In our study system plants have advanced more rapidly��than pollinators. If the trends continue, we may see plants flower before��pollinators become active in the future,” said Zoller, who is currently a postdoctoral associate at Cornell University in Ithaca, New York.

“Mismatches may occur among these currently overlapping pairs as plants and pollinators continue to respond differently to changing conditions,” she added.

Some species are already slipping out of sync.

The western bumblebee, for example, is emerging 12 days later than a century ago, which could leave it struggling to find enough food. Once common and widespread in the western United States and Canada, this species has due to a mix of disease, habitat loss and pesticides.

“This mismatch in the schedules of western bumblebees and the plants they historically fed on could add another stressor on top of everything else this species is facing,” Resasco said.

Pollinators, including domestic honeybees and wild species, contribute to the reproduction of 75% of the world’s flowering plants and about 35% of the world’s food crops. Their decline could have far-reaching effects on both natural landscapes and agriculture.

“Wild pollinators help maintain the biodiversity of plants in our ecosystems. We have a responsibility to make sure they don’t disappear,” Resasco said.��