May 23, 2014 at 4:59 pm #2365MikeKeymaster
Beyond Honeybees: Now Wild Bees and Butterflies May Be in Trouble
By now you probably know about the plight of America’s honeybees: the collapsed colonies and dying hives, threatening pollination services to crops and the future of a much-beloved insect.But it’s not just honeybees that are in trouble. Many wild pollinators—thousands of species of bees and butterflies and moths—are also threatened. Their decline would affect not only our food supply, but our landscapes, too.
Most honeybees live in commercially managed agricultural colonies; wild pollinators are caretakers of our everyday surroundings.“Almost 90 percent of the world’s flowering species require insects or other animals for pollination,” said ecologist Laura Burkle of Montana State University. “That’s a lot of plants that need these adorable creatures for reproduction. And if we don’t have those plants, we have a pretty impoverished world.”Compared to honeybees, wild pollinators are not well studied, and their condition has received relatively little public attention.
Most people don’t realize that there are thousands of bee species in the United States. Even many butterflies are overlooked, with the plight of just a few species, particularly monarchs, widely recognized.’Species that used to be in all our yards are dropping out.’Wild bees and butterflies are out on the landscape, making them difficult to count, and a lack of historical baselines makes it challenging to detect long-term trends. Slowly but surely, though, results from field studies and anecdotal reports from experts are piling up. They don’t paint a pretty picture.
Many pollinator populations seem to be dwindling.According to a recent survey organized by the Xerces Society, an invertebrate conservation group, nearly one-third of North American bumblebee species are declining. Other studies have reported similar trends, documenting dramatic declines in once-common species such as the American bumblebee.
If that’s happening to bumblebees, says Xerces Society executive director Scott Black, it’s quite possible, even likely, that others are hurting, too.“There’s very little information status on most of the bees other than bumblebees, but if you look at the life histories of these groups, many are likely even more sensitive to the disturbances leading to the declines, such as pesticides and habitat loss,” Black said.
“Although we don’t know what’s going on with all bees, I think we could be seeing real problems.”Among other pollinators, iconic monarch butterfly declines are well documented: Their numbers are now at a small fraction of historical levels. And entomologist Art Shapiro of the University of California, Davis spent most of the last four decades counting butterflies across central California, and found declines in every region.
These declines don’t just involve butterflies that require very specific habitats or food sources, and might be expected to be fragile, but so-called generalist species thought to be highly adaptable. Many other entomologists have told Black the same thing. “Species that used to be in all our yards are dropping out, but nobody’s monitoring them,” Black said.Plenty of blame to go around
Some of the factors behind the declines have also been implicated in honeybee die-offs. Like honeybees, wild pollinators are sensitive to pesticides, including neonicotinoids, an enormously popular class of insect-killers used in most major crops that has been linked to bee deaths.Their use has been restricted on farms in the European Union but continues on U.S. farms. They’re also used even more intensively in nurseries and gardens. What’s more, says Black, instructions on minimizing honeybee harm from pesticides, such as spraying them in the morning, may end up targeting other pollinators.
It’s difficult to quantify the harms caused by pesticides—not just neonicotinoids, but dozens of other chemicals, their effects varying by dose and combination—but “it’s logical to think they’re having some kind of effect,” said biologist Claire Kremen of the University of California, Berkeley. “It’s amazing we see as many pollinators as we do. Those are the ones who’ve survived this continuous pummeling.”Significant as pesticide impacts could be, though, they may be eclipsed by habitat loss. Across the United States, pollinator habitat is disappearing at rates usually reserved for descriptions of Amazon rain forest deforestation.
This is most striking in the Midwest, where more than 36,000 square miles of wetlands and prairie—an area larger than Indiana—has been converted to cropland since 2008.Farms don’t need to be bad for pollinators. The wetlands and drainage ditches of California’s rice fields provide valuable food and shelter to butterflies, Shapiro says. But in the Midwest and elsewhere, the widespread use of herbicide-resistant crop varieties has allowed farmers to apply herbicide more intensively than ever.
It’s now possible to wander a corn farm for days without seeing a single bee.Add urban and suburban development that produces landscapes of chemically maintained, regularly mowed lawns and roadsides, and “habitat loss is generally thought to be the most important factor driving bee declines,” wrote researchers in 2010.
What are the long-term consequences of pollinator loss? Presently it’s hard to say. In a given locale, losing a few species might have little effect, as others will take over their ecological role. Lose enough, though, and a tipping point might be reached, resulting in a collapse of pollinators and the plants that rely on them to reproduce.
“You can use the example of an airplane: Start to undo some rivets and screws, and it’s still going to fly, because there’s still redundancy in the system,” said Burkle. “But at some point it begins to fall apart.”
The interaction network of flowering plants (top) and pollinators (bottom) in an Illinois forest fragment. Black lines are relationships that have remained intact since the late 19th century; red and blue lines are relationships that have been lost.
It’s not yet possible to predict where that point will be, Burkle said, but stresses are already evident. In a 2013 Science paper, Burkle and colleagues described a 50 percent decline in bumblebee species in an Illinois forest. They also plotted network graphs of historical and present-day interactions between bees and plants. The comparison (above) shows a dramatically shrunken web of relationships.
Tipping point or not, such patterns could eventually translate into agricultural losses. Though most farmers rely on commercial honeybees, wild pollinators in the U.S. still provide an estimated $14.6 billion worth of pollination services every year. The oft-cited figure that one in every three bites of food was pollinated includes not just honeybees, but all pollinators.
‘Anybody can do something for pollinators.’Human diets aside, pollinators put food in the mouths of animals, too, and cultivate our landscapes. Nature’s verdancy is very much a result of countless billions of pollinators flying from flower to flower in an unceasing hum of activity.
“If there was a loss of pollinators,” said USDA entomologist Terry Griswold, “that would have a cascading effect in terms of forage for a good proportion of the biota.” In less technical terms, most of what lives relies on pollinated plants.If the situation seems grim, though, solutions do exist.
Researchers like Kremen and the University of Maine’s Frank Drummond have demonstrated the economic value of creating pollinator-friendly habitat on farms. Others have shown that it’s possible to get industrial-scale yields while using a minimum of pesticides and herbicides.Kremen noted that costs of helping pollinators are presently borne by farmers, who often want to help but can’t afford it.
“Our government has to step up and provide support for food growers to do this,” she said. The USDA did recently start a pollinator habitat restoration program; it’s still small, but it’s a beginning.The public can also play an important role. Griswold recommended that homeowners leave at least a bit of lawn unmowed—those so-called weeds are habitat and forage for pollinators—and cut back on herbicide and pesticide use. Even those small steps, he said, are quite helpful.
At a larger scale, conservation groups like Monarch Watch are working to create pollinator habitat along the butterfly migration route, a project that will require the participation of thousands of people.“I would like to see communities get together to have butterfly garden corridors running through them,” Shapiro said. “If you get five households on a city block, you’ve got a corridor.”“If we’re going to deal with these problems, we need to have everybody taking action,” Black said. “In the past, I worked to get wilderness designated—with salmon and spotted owls and wolves, with old growth and wild rivers.
That’s different than what I do now, because anybody can do something for pollinators.”
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