This time of year you can step out into a field of goldenrod or stand next to a wall of flowering Japanese knotweed and experience the frantic, almost hysterical activity of the late season bumblebees and honey bees as they dig into the flowers for nectar and pollen and relay their finds back to their colonies and hives. The bees sense that it is time to make winter food! They know that the summer bounty will soon be gone, and that survival of the honey bee colony or the mated queens of the bumblebees will only be possible if sufficient food resources are gathered and secured.
Bumblebees, in particular, are extremely important native pollinators of not only a significant number of wild plants but also many of the plants upon which we depend for food, forage and fiber (including cashews, peppers, watermelons, pears, peaches, apples, cherries, strawberries, raspberries, cranberries, cotton, clover, and tomatoes (and many more!)). A rich, robust bumblebee community, then, is important for ecological and also for economic reasons.
There was an article this summer (July 10, 2015 in Science) about bumblebees and the potential impact of climate change on their distribution across both North America and Europe. Jeremy Kerr (University of Ottawa) headed a group of thirteen co-authors who analyzed 110 years of data (more than four hundred thousand individual observations!) on the distribution of 67 species of bumblebees.
Kerr and his co-authors found, not surprisingly, that many bumblebee species were leaving the southern sections of the ranges in response to rising temperatures and changing vegetation. They also found, and this was quite surprising and more than a little disturbing, that these bumblebees were not then expanding their individual ranges to the north. Their distribution dimensions, then, were rapidly shrinking as the erosion pressures from the south pushed up against some sort of ecological barrier to the north.
What was the nature of this northern barrier? The impacts of changing temperature and moisture on many other insect species have clearly shown that both altitudinal and latitudinal migrations are common responses by species under climate change pressures. Why can’t bumblebees migrate northward like many of these other insect species? The problem, the authors speculate, has to do with the specific plants from which the bumblebee species gather their nectar and pollen. These plants on which the bumblebees depend simply are not found outside the northern edges of their ranges, and therefore, there is no food for the bumblebees in these apparently hospitable climate zones.
Is plant migration simply happening more slowly than the ongoing southern extirpation of the bumblebees, or are there some other barriers that are preventing the plants from expanding into these northern zones? Will the bumblebees have to evolve anatomically to be able to get nectar from a broader array of the more northern plant species? There was a recent paper (in September 25, 2015 issue of Science) that showed that bumblebees in Rocky Mountain ecosystems that are being affected by climate change have shorter tongues than they did just fifty years ago. Shorter tongues, the authors speculate, enable the bumblebees to effectively use a broader, more generalized set of plant species in their foraging and feeding.
So, we have some ideas, but the answers to these questions are not yet known. All we know is that bumblebee species are occupying smaller and smaller ecological zones all across North America and Europe.
Bumblebee extinction may accelerate because of climate change, but it has been an ongoing event in human modified ecosystems primarily due to habitat destruction and wildflower species loss. In England, a number of native bumblebee species have gone extinct in very recent times. A news story about programs designed to reverse these extinction events, though, was published this summer (August 11, 2015) in The BBC News. The short-haired bumblebee (Bombus subterraneous), a native bumblebee of southern England, was declared locally extinct in 2000 (no individuals of this species had been collected in England since 1988). A vigorous program to re-establish wildflower habitats in England (2500 acres of these habitats have been set up and maintained) coupled with the re-introduction of short-haired bumblebee queens from Sweden have succeeded in generating viable, reproducing populations of short-haired bumblebees throughout the south England countryside. Further, three other formerly locally extinct bumblebee species have similarly been re-introduced to England via foreign queens and these bumblebees are thriving in and around the maintained wildflower refuges.
Bumblebees are under a great deal of stress from habitat destruction, wildflower loss, and also pesticide and pathogen impacts. A paper published this past spring (April 25, 2015) in Nature showed that both honey bees and bumblebees were strongly attracted to nectars that contained neonicotinoid pesticides. These pesticides are commonly used for insect control on crops but have been linked to significant bee damage in many studies (The European Union has banned these pesticides because of their connections to high levels of bee mortality. Bills have been proposed in the US Congress to restrict the use several of these pesticides, but they were sent to committee and no definitive action was taken). This unexpected affinity of bees to these chemicals may explain why they are so toxic to these important pollinators.
To appreciate the influence of bees on their ecosystems one only has to consider the Galapagos Islands and the one type of bee that is naturally found there: the Galapagos carpenter bee (Xylocarpa darwinii). The Galapagos Islands have very simple ecosystems primarily because of the incredible difficulties involved in getting animals or plants across 600 miles of ocean to colonize them. That only one species of bee survived the journey is not at all surprising. This bee is the major pollinator on the islands (a few bird species also do some pollinating and the limited number of native moths and butterflies that are found there also do some pollination, but it is the Galapagos carpenter bee that accomplishes most of the pollen transfers in the archipelago). The ecological preferences and idiosyncrasies of this bee, then, should be expected to have impacts on the vegetative ecosystems that rely upon it. One of the most obvious impacts concerns flower color. The Galapagos carpenter bee is preferentially attracted to the color yellow. Flowers, then, that are yellow will be more likely to be visited by and therefore pollinated by Galapagos carpenter bees. Plants, then, with yellow flowers are more likely than plants with other colors of flowers to reproduce! As you travel across the Galapagos, you see the impact of this: almost all of the flowers on every island are yellow.
The role of bumblebees in natural ecosystems in pollinating wild plants and their activities in agricultural ecosystems to pollinate many of our essential crop plants make them an indispensable part of all of our biotic communities. Planting native plants in your gardens and flower beds, using minimal amounts of pesticides and herbicides (or better yet, none of these chemicals at all!), and allowing these important species safe places to make colonies in your yards and fields are all ways to help these organisms that do so much for us.