Are glacier lilies and bumble bees out of sync?

A new study, conducted in the Rocky Mountains of Colorado, suggests a disturbing relationship between climate change and the pollination rate of a specific flower, the glacier lily. The research—performed over a 17-year period by Professor James Thomson from the University of Toronto—is due to be published in Philosophical Transactions of the Royal Society B: Biological Sciences.

Scientists have been arguing for years about whether a “pollination deficit” actually exists. Bits and pieces of information accumulated over the course of about two decades seem to indicate that the number of pollinator species—as well as their population densities—is decreasing. Growers of many different crops—from blueberries in Canada to cherries in China—have reported a decreasing availability of pollinators.

The reasons for pollinator decline are many and include pesticide use, habitat loss, habitat fragmentation, poor nutrition, and parasitic mites. But the study by Professor Thomson is unique in that it attempted to measure the effects of climate change by controlling for the other factors.

Thomson and his group purchased a remote plot of land isolated from many of the common disturbances known to affect native pollinators. Furthermore, he based his study solely on a plant/pollinator combination native to the location where the research took place. No non-native species were introduced.

Thomson studied the pollination rate of the glacier lily. In the experiment, the fruiting rate (the number of successful pollinations) was compared between two groups of lilies—those pollinated by hand and those pollinated by native pollinators. Over the course of the 17 years the numbers continually diverged with the naturally-pollinated lilies producing fewer and fewer fruits as time went on. The divergence was especially great in the early spring.

Because the research plot was far from agricultural and population centers, Thomson believes that the major difference in the plant/pollinator environment over the 17-year period was that caused by climate change. He believes that the change in pollination rate is due to the divergence of bloom time and bumble bee emergence—a situation that can easily be brought about by climate change.

In nature, plants tend to respond more quickly to changes in temperature than insects. So while plants bloom earlier in warmer conditions, pollinators don’t emerge until a certain period of time has passed—causing the two events to happen on slightly different schedules. This is enough to cause losses in pollination, especially in the early spring—just as Thomson’s results demonstrate.

While this is just a small piece of the climate change puzzle, the information points to an area where more research is desperately needed. The more we know about the possible results of climate change, the better our policy decisions can be.

Rusty

Glacier lily. Flickr photo by Nordique.