08 Jul 2013: Report

Molecular Detective Work
Yields Big Gains for Ecology

The field of stable isotope analysis was once the realm of geologists and anthropologists. But rapid advances and plummeting costs mean that environmental scientists are increasingly using the technology to gain insight into the migration and behavior of various animals.

by madeline bodin

Jack Hopkins was in charge of the cracker shells, beanbag rounds, and rubber bullets. As the leader of a bear management crew in Yosemite National Park, he fired these deterrents at food-pilfering black bears from a 12-gauge shotgun. Each spring he attached radio collars to bears trapped among the crowded campgrounds of Yosemite Valley. After three years of chasing recalcitrant bears, however, he had questions.

How many bears in the park — especially outside of the valley — associated humans and their paraphernalia with food? Did the bears he hazed in campgrounds lose their taste for human food? Was there a better way to manage the interaction between bears and humans?

Other researchers had spent years tracking the radio signals of collared bears looking for answers to these questions, but Hopkins thought he had a better idea: To use a technique called stable isotope analysis — which had been employed for decades by geologists, archeologists, and climatologists — to answer his questions about the interaction of Yosemite’s bears with its human visitors. The isotopic signature of bear guard hairs would help tell the tale.

Stable isotope analysis relies on the fact that elements in different environments and foods contain different atomic signatures, based on the
Scientists are examining the lives of animals that are too small, too dangerous, or live too remote to study in other ways.
number of neutrons. For example, the ratio of a heavy nitrogen isotope to the common nitrogen isotope tends to increase as you move up the food chain from plant to predator. Oceans have an isotopic signature that is distinct from fresh water. Dry habitats have a different ratio of carbon isotopes than wet habitats. Deuterium, a heavy hydrogen isotope, tends to be proportionately high in clouds over tropical oceans. It decreases predictably the farther inland you go.

In recent years, the cost of stable isotope analysis has steadily fallen, and as a result Hopkins and other ecologists are using the technique to examine the lives of animals that are too small, too dangerous, or that live too remotely to study in other ways. Scientists are now using stable isotope analysis to piece together the migrations of dragonflies, to deduce the likely wintering grounds of songbirds, and to determine why animals feed in different areas based on pressure from predators.

“Stable isotope analysis has been adopted by ecologists recently,” says Seth Newsome, an assistant professor of biology at University of New Mexico. “Before that it was used by geologists, paleontologists, archeologists and climatologists — people who study deep time.”

Newsome, for example, has used stable isotopes to study the shifting diet of California condors from the Pleistocene era through the present by examining the ratio of the heavier carbon and nitrogen isotopes in their bones. His work has revealed that Pleistocene condors fed more on whales or other marine mammals that washed up on shore, while today’s condors
Stable isotopes have been used to study the shifting diet of California condors from the Pleistocene to the present.
show isotopic ratios consistent with a diet of land-based plant-eaters, particularly corn-fed feedlot cattle.

The ratio between stable isotopes is sorted out using a device called a mass spectrometer. The sample to be analyzed — a dragonfly wing, or a hair from a bear — is sealed in a metal capsule that is smaller than a thimble, placed into the spectrometer, burned into a gas, and then shot toward a magnet. The magnet deflects each atom at an angle relative to its weight, much the way a prism refracts a beam of light into its component colors by wavelength.

In the late 1990s, before the development of tracking devices small enough to be carried by songbirds, stable isotope analysis changed the study of songbird migration from a game of chance — waiting for a banded bird to be spotted again — to a laboratory exercise. In 1998, Peter Marra, then at Dartmouth College, published the first paper linking the quality of a songbird’s wintering grounds with its survival and breeding success. Science Magazine called it “the Holy Grail of avian ecology.”

Marra, now at the Smithsonian Institution’s Migratory Bird Center, used carbon isotopes in the blood samples of small songbirds — American redstarts — arriving on their New Hampshire breeding grounds to determine which had wintered in rich, wet habitats and which had wintered in poor, dry habitats. Birds wintering in lush habitats in Jamaica and Honduras, mostly older males, arrived first. Previous studies had shown that early birds sire more offspring.

“That carbon technique is still state of the art,” Marra says of his method to link habitat and diet.

Jack Hopkins
Montana State University
Ecologist Jack Hopkins collects bear hair samples in Yosemite National Park for stable isotope analysis.
For tracking bird migration, data loggers now exist that are small enough to affix to a songbird. But that is not the case with dragonflies. So Marra and Kent McFarland of the Vermont Center for Ecological Studies are using stable isotope analysis to track the migration of green darner dragonflies. Green darners are large for an insect — imagine a flying blue-green cigarette — but still too small to carry a tracking device and too delicate even for the stickers that have been used to trace monarch butterfly migrations. That dragonflies migrate has been known for millennia, says McFarland. How green darners move north in the spring is still a mystery, however.

McFarland and Marra’s dragonfly research will rely on that deuterium gradient, which in North America runs roughly north to south, to trace the green darners’ journey. McFarland hopes his green darner studies will reveal important migration points for the dragonflies so that those places can be conserved, if necessary. Throughout their lives, the dragonflies maintain the isotopic signature of the pond where they were larvae. The green darner research is possible because analyzing a tiny piece of dragonfly wing in the Smithsonian’s mass spectrometer now costs only about $8 — crucial for a project that has no major funding.

When Hopkins, the Yosemite bear researcher, decided to concentrate on using stable isotopes to analyze the bears’ diets, he needed access to a mass spectrometer and a stable isotope expert. He found both in the Earth and Planetary Sciences Department at the University of California, Santa Cruz, in the lab of Paul Koch, a vertebrate paleoecology researcher wise in the ways of both stones and bones. But analyzing the hundreds of bear hair samples that he had collected by stringing barbed wire around bait stations throughout the park was not going to be as easy as popping the hair into the mass spectrometer and reading the results. First, he had to lay the groundwork.

As Marra has found, site-specific variables — such as elevation, diet, the age of the animal, and the distance from the seacoast — can confound the
Isotopic signatures showed there were twice as many problem bears in Yosemite Park as anyone expected.
isotopic ratios found in different creatures. Those variables are a trap for unwary researchers, says Merav Ben-David a professor in the Department of Zoology and Physiology at the University of Wyoming who wrote several of the papers in a special feature in the Journal of Mammalogy last year on stable isotope analysis. “There are hundreds of papers out there that I consider unreliable because people didn’t quantify the underlying variations,” she says.

Hopkins — now a post-doctoral researcher at the University of Alberta and Peking University — figured out the underlying variables for his bear study by analyzing human hair samples from a barber shop in St. Louis, hair samples from Yosemite black bears known to eat human food, bears known not to eat human food, and samples of just about any food a bear might eat in the backcountry, from berries to mule deer. The various samples allowed him to compare the isotope ratios in the bear hair to the actual, natural food the bears would eat in Yosemite.

Once he compared the isotopic signatures in the hair of about 300 bears from around Yosemite, Hopkins found that there were four additional bears in the busy Yosemite Valley that were conditioned to human food that the bear managers didn’t know about, in addition to about 20 that they did know about. The big surprise was how many bears in the backcountry – 15 — were also eating human food. There were twice as many problem bears in the park than previously known. Bears that had been identified as eating human food in an earlier study stayed human-food eaters in this study; scaring or moving bears was not changing their behavior.

MORE FROM YALE e360

Counting Species: What It Says
About Human Toll on Wildlife

Klinkenborg Counting Species: What It Says About Human Toll on Wildlife
By analyzing mitochondrial DNA, scientists now can make more accurate estimates of the numbers of individual species that existed centuries ago. Verlyn Klinkenborg explores what it is telling us about our impact on the natural world and about our own future.
READ MORE
Hopkins’ bear studies have provided scientific confirmation for bear-management changes already underway in Yosemite National Park. Park officials are still firing bean bag rounds at Yosemite Valley’s recalcitrant bears, but this year, among other changes, the park has increased efforts to prevent bears in the backcountry from ever tasting human food.

Ben-David says that such isotope research enables researchers to look beyond just diet to broader animal behavior. Her 2004 paper in Oecologia used nitrogen isotopes to show that female Alaskan brown bears with young cubs sometimes avoid salmon streams, forgoing a feast in order to keep their cubs safe from other bears. A 2007 study by University of Victoria conservation scientist Chris Darimont discovered that black-tailed deer pay for feeding in richer habitats by becoming more likely prey for wolves.

Ben-David admits that it is impossible to know where the cutting edge of ecological stable isotope studies will be in two years. “This field is moving very fast,” she says. So fast, that when she was recently asked to compile some papers on ecological studies using stable isotopes into a book, she refused.

“By the time it’s published,” she says, “it will be ancient history.”

POSTED ON 08 Jul 2013 IN Climate Policy & Politics Science & Technology Sustainability Europe North America 

COMMENTS


Very excited to apply stable isotopes for ecological studies in Himalaya. Great job Jack. Proud to be associated with you.

Posted by Bikash Adhikari on 13 Jul 2013


POST A COMMENT

Comments are moderated and will be reviewed before they are posted to ensure they are on topic, relevant, and not abusive. They may be edited for length and clarity. By filling out this form, you give Yale Environment 360 permission to publish this comment.

Name 
Email address 
Comment 
 
Please type the text shown in the graphic.


madeline bodinABOUT THE AUTHOR
Madeline Bodin is a freelance writer specializing in wildlife conservation science. She lives in Vermont. Her writing has explored the fate of New England’s largest bat cave, the forensic techniques used to solve wildlife crimes, and the mafia-like tactics of cowbirds. Her work has appeared in Scientific American, Popular Mechanics, National Wildlife, and many other publications.

 
 

RELATED ARTICLES


Global Extinction Rates: Why
Do Estimates Vary So Wildly?

Is it 150 species a day or 24 a day or far less than that? Prominent scientists cite dramatically different numbers when estimating the rate at which species are going extinct. Why is that?
READ MORE

Probing the Rich Inner Lives
Of the Planet’s Wild Animals

Scientist Carl Safina has examined our steadily evolving understanding of the complex interactions among the more social members of the animal world. In an interview with Yale Environment 360, he talks about why it’s vital to our humanity to empathize more deeply with wild creatures.
READ MORE

Resilience: A New Conservation
Strategy for a Warming World

As climate change puts ecosystems and species at risk, conservationists are turning to a new approach: preserving those landscapes that are most likely to endure as the world warms.
READ MORE

Oklahoma’s Clear Link Between
Earthquakes and Energy Boom

Oklahoma officials this week said oil and gas activity was the likely cause of the stunning increase in earthquakes in the state. In an interview with Yale Environment 360, Oklahoma geologist Todd Halihan talks about what has caused this growing problem and what can be done about it.
READ MORE

On the Internet, Illegal Trade
In Endangered Wildlife Thrives

On eBay and elsewhere on the Internet, illegal wildlife and wildlife parts — from elephant ivory to tiger skins to monkey and crocodile skulls — are being sold. Bringing an end to this illicit activity is proving to be a daunting challenge.
READ MORE

 

MORE IN Reports


As Ocean Waters Heat Up,
A Quest to Create ‘Super Corals’

by nicola jones
With the world’s coral reefs increasingly threatened by warmer and more acidic seas, scientists are selectively breeding corals to create species with the best chance to survive in the coming century and beyond. Are genetically modified corals next?
READ MORE

A Clash of Green and Brown:
Germany Struggles to End Coal

by christian schwagerl
A recent battle over imposing a “climate fee” on coal-fired power plants highlights Germany’s continuing paradox: Even as the nation aspires to be a renewable energy leader, it is exploiting its vast reserves of dirty brown coal.
READ MORE

On an Unspoiled Caribbean Isle,
Grand Plans for Big Tourist Port

by fred pearce
East Caicos is a tropical jewel – the largest uninhabitated island in the Caribbean and home to rare birds and pristine turtle-nesting beaches. But plans for a giant port for cruise and cargo ships could change it forever.
READ MORE

A Little Fish with Big Impact
In Trouble on U.S. West Coast

by elizabeth grossman
Scientists are concerned that officials waited too long to order a ban on U.S. Pacific sardine fishing that goes into effect July 1. The dire state of the sardine population is a cautionary tale about overharvesting these and other forage fish that are a critical part of the marine food web.
READ MORE

Despite Hurdles, Solar Power in
Australia Is Too Robust to Kill

by jo chandler
No nation has as high a penetration of residential solar as Australia, with one in five homes now powered by the sun. And while the government has slashed incentives, solar energy continues to grow, thanks to a steep drop in the cost of PV panels and the country’s abundant sunshine.
READ MORE

Genetically Modified Mosquito
Sparks a Controversy in Florida

by lisa palmer
Officials in the Florida Keys are seeking to use a GM mosquito that could help prevent a recurrence of dengue fever there. But fears among some residents — which scientists say are unfounded — are slowing the release of mosquitoes whose offspring are genetically programmed to die.
READ MORE

Oasis at Risk: Oman’s Ancient
Water Channels Are Drying Up

by fred pearce
Since pre-Islamic times, Oman’s water systems known as aflaj have brought water from the mountains and made the desert bloom. But now, unregulated pumping of groundwater is depleting aquifers and causing the long-reliable channels to run dry.
READ MORE

Surge in Renewables Remakes
California’s Energy Landscape

by cheryl katz
Thanks to favorable geography, innovative government policies, and businesses that see the benefits of clean energy investments, California is closing in on its goal of generating a third of its electricity from renewables by 2020.
READ MORE

As Andes Warm, Deciphering
The Future for Tropical Birds

by daniel grossman
Scientists have theorized that tropical birds in mountainous regions will move uphill as the climate warms. But new research in the Peruvian Andes suggests that the birds will stay put and face a new threat — predator snakes that will climb into their territory to escape the heat.
READ MORE

Can the North Sea Wind Boom
And Seabird Colonies Coexist?

by fred pearce
Offshore wind farms have been proliferating in the North Sea, with more huge projects planned. But conservationists are concerned this clean energy source could threaten seabird colonies that now thrive in the sea’s shallow waters.
READ MORE


e360 digest
Yale
Yale Environment 360 is
a publication of the
Yale School of Forestry
& Environmental Studies
.

SEARCH e360



Donate to Yale Environment 360
Yale Environment 360 Newsletter

CONNECT


ABOUT

About e360
Contact
Submission Guidelines
Reprints

E360 en Español

Universia partnership
Yale Environment 360 articles are now available in Spanish and Portuguese on Universia, the online educational network.
Visit the site.


DEPARTMENTS

Opinion
Reports
Analysis
Interviews
Forums
e360 Digest
Podcasts
Video Reports

TOPICS

Biodiversity
Business & Innovation
Climate
Energy
Forests
Oceans
Policy & Politics
Pollution & Health
Science & Technology
Sustainability
Urbanization
Water

REGIONS

Antarctica and the Arctic
Africa
Asia
Australia
Central & South America
Europe
Middle East
North America

e360 PHOTO GALLERY

“Cuba
Photographer Robert Wintner documents the exquisite beauty and biodiversity of Cuba’s unspoiled coral reefs.
View the gallery.

e360 MOBILE

Mobile
The latest
from Yale
Environment 360
is now available for mobile devices at e360.yale.edu/mobile.

e360 VIDEO

Warriors of Qiugang
The Warriors of Qiugang, a Yale Environment 360 video, chronicles a Chinese village’s fight against a polluting chemical plant. It was nominated for a 2011 Academy Award for Best Documentary Short.
Watch the video.


header image
Top Image: aerial view of Iceland. © Google & TerraMetrics.

e360 SPECIAL REPORT

“Tainted
A three-part series Tainted Harvest looks at the soil pollution crisis in China, the threat it poses to the food supply, and the complexity of any cleanup.
Read the series.

OF INTEREST



Yale