Research by the University of Toronto’s ecology department has made a startling find: bee pollinators are on the decline.
The 17-year-long study led by Prof. James Thomson — known to most as the ecology instructor in BIO150 — has attributed the steady pollinator decrease to the effects of global warming. The study found that the flowering rates of the Glacier Lily, Erythronium grandiflorum, a flower found in western North America, had decreased significantly over the course of the study — a strong indicator of an absent bee population, the lily’s primary pollinator.
The study took place on a remote plot of land purchased by Thomson in the Rocky Mountains of Colorado, and required examining two sets of Glacier Lilies. One set was pollinated regularly by hand, while the other set was allowed to be pollinated naturally. The study found that relative to the control, the second set was flowering significantly less.
In his paper, Thomson lists three possible explanations: either the pollinator populations have declined, the lily flowering and pollinator emergence have become less synchronous, or pollinators have shifted their activity away from the lilies, presumably by visiting other plant species. Thomson is quick to dismiss the third explanation, since the only other flower species existing in the area has not changed in density or timing of flowering.
The second explanation, he argues, represents a growing phenological mismatch between E. grandiflorum and its best pollinators — in other words, the life cycles of the plant and pollinator are no longer in sync. This could be due to the early blooming of the Glacier Lily, which sensitive to recent temperature increases, while bumblebees’ emergence from hibernation occurs much later.
Thomson is not the first ecologist to make such a claim about the effects of climate change on organism-environment relationships. He references a similar paper by researchers from the University of Maryland, which states that migrating birds, signaled by rising air temperatures, are arriving earlier than the start of the local growing season which is controlled by the melting of the previous year’s snowpack. What’s more, present data is indicating that American Robins are arriving 14 days earlier than they did in 1981, and the interval between their arrival date and the first date of bare ground has increased by 18 days. The paper also mentions the effects of climate change on hibernation behaviour in yellow-bellied marmots, which are emerging 38 days earlier than they were 23 years ago, apparently in response to rising spring air temperatures.
Thomson’s first possible explanation for the decreased Glacier Lily flowering rates cites a declining pollinator population, and brings to mind the phenomenon known as Colony Collapse Disorder. Since 2006, numerous reports have been accumulating on a global drop in bee populations, observed mainly in Europe and North America. Although the causes of the syndrome are still unknown, many researchers attribute CCD to biotic factors like mites, and insect diseases such as pathogens, malnutrition, pesticides, and even stresses related to environmental change.
Although the long-term ecological consequences of a global decline in bee populations is still not fully understood, there is no denying the importance of bees to agriculture and plant diversity. In fact, about 35 per cent of the world’s crop production is dependent on pollinators such as bees, bats, and birds. Similar studies in tropical regions where plant diversity is high and heavily dependent on bees found plants to be frequently insufficiently pollinated.
In an interview with the CBC, Thomson cautions, “To my mind, it gives some additional legitimacy to that concern that pollination systems are in trouble.” He recalls how at the start of the study two decades ago, he saw no evidence that the bees were in decline. “My general sense from walking around in field is that there are as many as there used to be.”
With regard to the significance his study holds to the continuing debate on climate change, Thompson explains, “If the flowers are starting so early that the weather is really bad, bees may have broken out of their hibernation, but they may not be working that hard visiting flowers.”
However, he explains that the findings may not be applicable to other plants, and cautions to keep the nature of similar studies in context. “You can’t look at questions about the effects of climate change with short-term studies,” he said. “You simply need a pretty extensive time span to detect whether an effect is worth paying attention to or not.”
