Monday, July 22, 2013

Bees ‘betray’ their flowers when pollinator species decline

The findings suggest that "global declines in pollinators could have a bigger impact on flowering plants and foods than previously realized," says ecologist Berry Brosi.

By Carol Clark

Remove even one bumblebee species from an ecosystem and the impact is swift and clear: Their floral “sweethearts” produce significantly fewer seeds, a new study finds.

The study, to be published by the Proceedings of the National Academy of Sciences, focused on the interactions between bumblebees and larkspur wildflowers in Colorado’s Rocky Mountains. The results show how 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 impact on flowering plants and food crops than was previously realized.”

The National Science Foundation (NSF) funded the study, co-authored by ecologist Heather Briggs of the University of California-Santa Cruz.

About 90 percent of plants need animals, mostly insects, to transfer pollen between them so that 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, sparking research into the potential impact of such declines.

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.

Emory University ecologist
Berry Brosi led the study.
Brosi and Briggs were curious whether this theoretical resilience would hold up in real-life scenarios. Their 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 lifetime, but often they will display what we call floral fidelity over shorter time periods,” Brosi explains. “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 experiments were done at the Rocky Mountain Biological Laboratory near Crested Butte, Colorado. 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 of the 11 bumblebee species there.

Watch a video about the Rocky Mountain Biological Laboratory: 

The study included a series of 20-meter square wildflower plots. Each was evaluated in a control state, left in its natural condition, and in a manipulated state, in which bumblebees of just one species had been removed using nets.

“We’d literally follow around the bumblebees as they foraged,” Briggs says, describing how they observed the bee behavior. “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.

“Running around after bumblebees in these beautiful wildflower meadows was one of the most fun parts of the research,” Brosi says. Much of this “bee team” was made up of Emory undergraduate students, funded by the college’s Scholarly Inquiry and Research at Emory (SIRE) grants and NSF support via the Research Experience for Undergraduates (REU) program.

The Rocky Mountain Biological Laboratory is exacting about using non-destructive methodologies so that researchers don’t have a negative impact on the bumblebee populations. “When we caught bees to remove target species from the system, or to swab their bodies for pollen, we released them unharmed when our experiments were over,” Brosi says. “They’re very robust little creatures.”

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 the manipulated groups carried more different types of pollen on their bodies than those in the control groups.

These changes had direct implications for plant reproduction: Larkspurs produced about one-third fewer seeds when one of the bumblebee species was removed, compared to the 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 back to the broader functioning of an ecosystem.

“Our work shows why biodiversity may be key to conservation of an entire ecosystem,” Brosi says. “It has the potential to open a whole new set of studies into the functional implications of interspecies interactions.”

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Friday, July 12, 2013

Why the future of fuel lies in artificial photosynthesis

By Carol Clark

Most people, especially technical experts, may agree that we have an energy crisis, but it’s much harder to come to a consensus on how to solve it.

Fossil fuels, wind power, biofuels, geothermal power, nuclear energy and solar power are all pieces in the puzzle for how to keep Earth’s burgeoning civilization running, says Emory inorganic chemist Craig Hill.

He adds, however, that an energy source that will be essential to manage the crisis in the coming decades is the least developed: Artificial photosynthesis.

Hill and other top experts in the nascent field of artificial photosynthesis co-wrote an opinion piece on the topic published in the journal Energy and Environmental Science.

“Humanity is on the threshold of a technological revolution that will allow all human structures across the earth to undertake photosynthesis more efficiently than plants,” the authors write.

The 18 authors on the opinion piece, from leading research universities and national laboratories in the United States, Europe and Australia, represent the broad range of expertise, from chemistry to biology to engineering, working on the problem.

The aim of artificial photosynthesis is to use solar energy to split water, to generate hydrogen as a cheap and abundant source of carbon-free fuel.

“The development and global deployment of such artificial photosynthesis (AP) technology,” the authors write, “addresses three of humanity’s most urgent public policy challenges: to reduce anthropogenic carbon dioxide emissions, to increase fuel security and to provide a sustainable global economy and ecosystem. Yet, despite the considerable research being undertaken in this field … AP remains largely unknown in energy and climate change public policy debates.”

“Globally, our energy requirements our expected to double in the next 30 to 40 years, maybe less,” Hill says. “It’s a staggering problem that puts everything else in perspective. Everything derives from energy. If we don’t have enough energy, we’re not going to have enough food and water.”

Fracking has opened up new sources of fossil fuels in the United States, but ultimately fossil fuels are going to run out. Fossil fuel use is also coming at a rapidly escalating environmental cost, including rising global temperatures and acidification of the oceans.

The only energy source that can come close to sustainably powering our long-term needs is terrestrial sunlight, Hill says.

The solar power industry, which converts sunlight into electricity, continues to grow, but it has severe limitations, Hill says. A great deal of space is required for solar panels to collect the sun’s energy, and that energy must be stored in batteries.

“We’re at the point now where we have solar powered buildings and electric cars, but we are never going to be able to run airplanes and ships and most other forms of transportation on electricity,” Hill says. “That’s why we ultimately need artificial photosynthesis, which is just another way of saying solar fuel.”

The goal of artificial photosynthesis is to do what plants do, only better.

“Plants use sunlight, water and carbon dioxide to make fuel in the form of carbohydrates,” Hill explains. “The process, however, is incredibly inefficient. It works for plants because they don’t have to worry about finances.”

Scientists currently know how to mimic plant photosynthesis, but not in ways that are powerful and efficient enough for practical application. Breakthroughs are needed in both fundamental science and materials engineering, says Hill, who is working on perfecting a key aspect of the problem, a water oxidation catalyst. Hill’s lab has developed the fastest homogeneous water oxidation catalyst to date.

“Artificial photosynthesis is a tremendous challenge,” Hill says, “but it’s also tremendously exciting.”

Hill foresees that we will eventually make the necessary breakthroughs to generate solar fuel. We simply have no other choice, he adds, as the human population approaches 10 billion by 2050.

Meanwhile, Hill and the co-authors of the Energy and Environmental Science opinion piece are calling for a globalized approach to artificial photosynthesis, to help raise the field’s public policy profile, remove logistical and governmental hurdles to its development, and strengthen an international commitment to clean, sustainable energy.

They envision scenarios like a network of light capture facilities situated in coastal cities where seawater would be catalytically converted to hydrogen and oxygen.

“Photosynthesis is the great invention of life,” they write. “Like biodiversity, the atmosphere, the moon, outer-space, the human genome and the world’s cultural and natural heritage, it could be treated as subject to common heritage requirements under international law, perhaps through a specific UN or UNESCO declaration. Common heritage of humanity status putatively limits private or public appropriation; requires representatives from all nations to manage such resources on behalf of all, actively share the benefits, restrain from their militarization and preserve them for the benefit of future generations.”

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Monday, July 8, 2013

A voice for the science of sustainability

Emory anthropologist Peggy Barlett studies the intersection of economic, ecological and demographic change among farmers around the world. She is also a key player in moving higher education to the forefront of sustainability.

“There are so many ways that our culture right now is in transition,” she says. “As an anthropologist I see a whole shift in the challenges we face and the ways in which universities, governments and faith communities are trying to contribute. Higher education has so many tools and so many talents to offer, I think it’s incredibly important to make sure that what we know is available to the general public.”

Barlett is part of the Public Voices Thought Leadership Fellowship at Emory. A collaboration with The OpEd Project, the program is designed to cultivate a sense of social responsibility and to increase the number of women involved in public debate. Check out the web site of the program’s lead sponsor, the Center for Women at Emory, to learn more.

How a natural leader bloomed