STUDY SHOWS ROCKY MOUNTAIN WILDFLOWER SEASON HAS LENGTHENED

FROM:  NATIONAL SCIENCE FOUNDATION 
Rocky Mountain wildflower season lengthens by more than a month

39-year bloom count reveals changes attributed to warmer climate
A 39-year study of wildflower blooms in a Colorado Rocky Mountain meadow shows that more than two-thirds of alpine flowers have changed their blooming patterns in response to climate change.

Not only are half the flowers beginning to bloom weeks earlier, but more than a third are reaching their peak blooms earlier, and others are producing their last blooms later in the year.

The blooming season, which used to run from late May through early September, now lasts from late April to late September, according to University of Maryland ecologist David Inouye.

The wildflower records, made up of more than two million blooms, suggest that flowering plants' responses to climate change are more complex than previously believed, with different species responding in unexpected ways.

The combinations of flowering species that bloom together are changing, too, with potential effects on insects and birds.

Studies that focus only on the date of flowers' first blooms--as most do--understate these changes, says Inouye, co-author of a paper published in this week's issue of the journal Proceedings of the National Academy of Sciences (PNAS).

"Long-term data are essential to understanding every environmental challenge the world faces," says Saran Twombly, a program director in the National Science Foundation's (NSF) Division of Environmental Biology, which funded the research.

"This study relies on long-term data to drive home the fact that species' responses to climate change are complex."

Phenology, the study of the timing of seasonal events, is crucial to knowing how climate change affects plants, animals and the relationships that bind them into natural communities.

To answer these questions, phenologists are collecting new data and poring through old records, such as amateur naturalists' notebooks.

"Most studies rely on first dates of events like flowering or migration because they use historical data sets that were not intended as scientific studies," Inouye says.

"First flowering is easy to observe. You don't have to take the time to count flowers. So that's often the only information available.

"It's taken a lot of effort to get the comprehensive insights needed for this analysis, which helps us understand how ecological communities may change in the future."

By counting blooms in each of 30 plots every other day, up to five months per year, for four decades, Inouye and colleagues amassed a data set including more than two million flowers.

For the study, University of Arizona biologist Paul CaraDonna, University of Maryland biologist Amy Iler and Inouye analyzed data on the 60 most common species.

Bloom times are changing fast, the researchers found.

The date the first spring flower appears has advanced by more than six days per decade over the course of the study.

The spring peak, when masses of wildflowers burst into bloom, has moved up by five days per decade.

And the last flower of fall occurred about three days later every decade. "The flowering season is about one month longer than it used to be," Iler says, "which is a big change for a mountain ecosystem with a short growing season."

Of all the species that have changed their flowering schedules in some way, only 17 percent shifted their entire bloom cycles earlier. The rest showed more complicated changes.

"First flowering isn't always the best predictor of all the changes we find," CaraDonna says.

"There's a lot more going on than you can get from this single, simple measure. So, it's important to take a closer look to understand all the ways climate change affects these wildflower communities."

As the plants' bloom patterns continue to change, researchers expect that some plants that bloomed simultaneously will no longer overlap, and others will start blooming together for the first time.

Ecologists refer to these new combinations as "'no-analog' communities."

"We usually think of no-analog communities as something that happens when plants or animals move into areas where they haven't lived before, creating novel combinations of species," Iler says.

"For example, we have red foxes at our study site now. It used to be too cold for them in winter. Now the marmots that live there have to deal with a new predator.

"But this study shows that even when species don't actually move, changes in the timing of key events in their life cycles may also result in no-analog communities, where species may interact differently than before."

The changes are likely to have a strong effect--for better or worse--on pollinating insects and migratory birds.

For example, Inouye says, hummingbirds that summer in the Rocky Mountains time their nesting so their eggs hatch at peak wildflower bloom, when there is plenty of flower nectar for hungry chicks.

But as the bloom season lengthens, the plants are not producing more flowers. The same number of blooms is spread out over more days, so at peak bloom there may be fewer flowers.

Will there be enough food for the hummingbirds' young?

To find out, Inouye plans to fit adult hummingbirds with radio transmitters to study how they interact with this summer's blooms.

-NSF-

DECLINE OF THE POLLINATORS

FROM:  NATIONAL SCIENCE FOUNDATION
Bee Faithful? Plant-Pollinator Relationships Compromised When Bee Species Decline

Remove even one bumblebee species from an ecosystem and the effect is swift and clear: Pollination is less effective, and plants produce significantly fewer seeds.

This according to research published today in the journal Proceedings of the National Academy of Sciences that focuses on the interactions between bumblebees and larkspur wildflowers in Colorado's Rocky Mountains.

The findings show that reduced competition among pollinators disrupts floral fidelity, or specialization, among the remaining bees in the system, leading to less successful plant reproduction.

"We found that these wildflowers produce one-third fewer seeds in the absence of just one bumblebee species," says Emory University ecologist Berry Brosi, who led the study.

"That's alarming and suggests that global declines in pollinators could have a bigger effect on flowering plants and food crops than was previously realized."

The National Science Foundation (NSF) funded the research; the paper was co-authored by ecologist Heather Briggs of the University of California-Santa Cruz.

"This study shows that the loss of a single bee species can harm pollination and reproduction of all flowering plant species in an ecosystem," says Alan Tessier, program director in NSF's Division of Environmental Biology, which funded the research.

"What's equally impressive is the demonstration of the mechanisms--that the loss of a single species changes the foraging behavior of all the remaining bee species."

About 90 percent of plants need animals, mostly insects, to transfer pollen between them so they can fertilize and reproduce.

Bees are by far the most important pollinators worldwide and have co-evolved with the floral resources they need for nutrition.

During the past decade, however, scientists have reported dramatic declines in populations of some bee species.

Some studies have indicated that plants can tolerate losing most pollinator species in an ecosystem as long as other pollinators remain to take up the slack. Those studies, however, were based on theoretical computer modeling.

Brosi and Briggs were curious about whether this theoretical resilience would hold up in real-life scenarios.

The team conducted field experiments to learn how the removal of a single pollinator species would affect the plant-pollinator relationship.

"Most pollinators visit several plant species over their lifetimes, but often will display what we call floral fidelity over shorter time periods," Brosi says.

"They'll tend to focus on one plant while it's in bloom, then a few weeks later move on to the next species in bloom. You might think of them as serial monogamists."

Floral fidelity clearly benefits plants, because a pollinator visit will only lead to plant reproduction when the pollinator is carrying pollen from the same plant species.

"When bees are 'promiscuous,' visiting plants of more than one species during a single foraging session, they are much less effective as pollinators," Briggs says.

The researchers conducted their experiments at the Rocky Mountain Biological Laboratory near Crested Butte, Colo.

Located at 9,500 feet, the facility's subalpine meadows are too high for honeybees, but they are buzzing during the summer months with bumblebees.

The experiments focused on the interactions of the insects with larkspurs, dark purple wildflowers that are visited by 10 of the 11 bumblebee species there.

The researchers studied a series of 20-meter-square wildflower plots, evaluating each one in both a control state, left in its natural condition, and in a manipulated state, in which nets were used to remove the bumblebees of just one species.

The researchers then observed bumblebee behavior in both the control plots and the manipulated plots.

"We'd literally follow around the bumblebees as they foraged," Briggs says. "It's challenging because the bees can fly pretty fast."

Sometimes the researchers could only record between five and 10 movements, while in other cases they could follow the bees to 100 or more flowers.

"When we caught bees to remove target species from the system, or to swab their bodies for pollen, we released them unharmed," Brosi says.

No researchers were harmed either, he adds. "Stings were very uncommon during the experiments. Bumblebees are quite gentle on the whole."

Across the steps of the pollination process, from patterns of bumblebee visits to plants, to picking up pollen, to seed production, the researchers saw a cascading effect of removing one bee species.

While about 78 percent of the bumblebees in the control groups were faithful to a single species of flower, only 66 percent of the bumblebees in the manipulated groups showed such floral fidelity.

The reduced fidelity in manipulated plots meant that bees in those groups carried more types of pollen than those in the control groups.

The changes had direct implications for plant reproduction: Larkspurs produced about one-third fewer seeds when one of the bumblebee species was removed, compared to larkspurs in the control groups.

"The small change in the level of competition made the remaining bees more likely to 'cheat' on the larkspur," Briggs says.

While previous research has shown how competition drives specialization within a species, the bumblebee study is one of the first to link this mechanism to the broader functioning of an ecosystem.

"Our work shows why biodiversity may be key to the conservation of an entire ecosystem," Brosi says.

"It has the potential to open a whole new set of studies into the implications of interspecies interactions."

-NSF-