OCEAN PHOSPHORUS CYCLE AND THE ROLE OF MICROBES

FROM:  NATIONAL SCIENCE FOUNDATION
Revealing the ocean's hidden fertilizer
Tiny marine plants play major role in phosphorus cycle
Phosphorus is one of the most common substances on Earth.

An essential nutrient for every living organism--humans require approximately 700 milligrams per day--we're rarely concerned about consuming enough because it is in most of the foods we eat.

Despite its ubiquity and living organisms' dependence on it, we know surprisingly little about how it moves, or cycles, through the ocean environment.

Scientists studying the marine phosphorous cycle have known that phosphorus was absorbed by plants and animals and released back to seawater in the form of phosphate as these plants and animals decay and die.

But a growing body of research hints that microbes in the ocean transform phosphorus in ways that remain a mystery.

Hidden role of ocean's microbes

A new study by a research team from the Woods Hole Oceanographic Institution (WHOI) and Columbia University reveals for the first time a marine phosphorus cycle that is much more complex than previously thought.

The work also highlights the important but previously hidden role that some microbial communities play in using and breaking down forms of this essential element.

A paper reporting the findings is published this week in the journal Science.

"A reason to be excited about this elegant study is in the paper's last sentence: 'the environmental, ecological and evolutionary controls ...remain completely unknown,'" says Don Rice, program director in the National Science Foundation's (NSF) Division of Ocean Sciences, which funded the research through its Chemical Oceanography Program. "There's still a lot we don't know about the sea."

The work is also supported by an NSF Dimensions of Biodiversity grant.

"This is an exciting new discovery that closes a fundamental knowledge gap in our understanding of the marine phosphorus cycle," says the paper's lead author Ben Van Mooy, a biochemist at WHOI.

Much like phosphorus-based fertilizers boost the growth of plants on land, phosphorus in the ocean promotes the production of microbes and tiny marine plants called phytoplankton, which compose the base of the marine food chain.

Phosphonate mystery

It's been unclear exactly how phytoplankton are using the most abundant forms of phosphorus found in the ocean--phosphates and a strange form of phosphorus called phosphonates.

"Phosphonates have always been a huge mystery," Van Mooy says.

"No one's been able to figure out exactly what they are, and more importantly, if they're made and consumed quickly by microbes, or if they're just lying around in the ocean."

To find out more about phosphonates and how microbes metabolize them, the researchers took samples of seawater at a series of stations during a research cruise from Bermuda to Barbados.

They added phosphate to the samples so they could see the microbes in action.

The research team used ion chromatography onboard ship for water chemistry analyses, which allowed the scientists to observe how quickly microbes reacted to the added phosphate in the seawater.

"The ion chromatograph [IC] separates out the different families of molecules," explains Van Mooy.

"We added radioactive phosphate, then isolated the phosphonate to see if the samples became radioactive, too. It's the radioactive technique that let us see how fast phosphate was transformed to phosphonate."

Enter the microbes

The researchers found that about 5 percent of the phosphate in the shallow water samples was taken up by the microbes and changed to phosphonates.

In deeper water samples, which were taken at depths of 40 and 150 meters (131 feet and 492 feet), about 15 to 20 percent of the phosphates became phosphonates.

"Although evidence of the cycling of phosphonates has been mounting for nearly a decade, these results show for the first time that microbes are producing phosphonates in the ocean, and that it is happening very quickly," says paper co-author Sonya Dyhrman of Columbia University.

"An exciting aspect of this study was the application of the IC method at sea. In near-real-time, we could tell that the phosphate we added was being transformed to phosphonate."

Better understanding of phosphorus cycle

A better understanding of phosphorus cycling in the oceans is important, as it affects the marine food web and, therefore, the ability of the oceans to absorb atmospheric carbon dioxide.

The researchers say that solving the mystery of phosphonates also reinforces the need to identify the full suite of phosphorus biochemicals being produced and metabolized by marine microbes, and what physiological roles they serve for these cells.

"Such work will help us further resolve the complexities of how this critical element is cycled in the ocean," Dyhrman adds.

Grants from the Simons Foundation also supported the work.

-NSF-
Media Contacts
Cheryl Dybas, NSF

STUDY SUGGESTS HABITAT FRAGMENTATION HAS WORLDWIDE NEGATIVE IMPACT

FROM:  NATIONAL SCIENCE FOUNDATION
Shrinking habitats have adverse effects on world ecosystems--and ultimately people

Extensive study of global habitat fragmentation points to major trouble ahead
An extensive study of global habitat fragmentation--the division of habitats into smaller and more isolated patches--points to major trouble for the world's ecosystems.

The study shows that 70 percent of existing forest lands are within a half-mile of forest edges, where encroaching urban, suburban and agricultural influences can cause harmful effects such as losses of plant and animal species.

Five continents of habitat fragmentation

The research also tracks seven major experiments on five continents that examine habitat fragmentation and finds that fragmented habitats reduce the diversity of plants and animals by 13 to 75 percent.

The largest effects are found in the smallest and most isolated fragments of habitat.

Results of the study, which involved two dozen researchers across the globe, are reported in a new paper published in Science Advances.

The work is funded by the National Science Foundation (NSF).

"The results are stark," said Doug Levey, program director in NSF's Division of Environmental Biology and a co-author of the paper. "No matter the place, habitat or species, habitat fragmentation has large effects, which grow worse over time."

The scientists assembled a map of global forest cover and found very few forest lands unencumbered by some type of human development.

World's forests shrinking

"It's no secret that the world's forests are shrinking, so we asked about the effects of this habitat loss and fragmentation on the remaining forests," said Nick Haddad, a biologist at North Carolina State University and corresponding author of the paper.

"The results were astounding," he said.

"Nearly 20 percent of the world's remaining forests are the distance of a football field--or about 100 meters--away from forest edges. Seventy percent of forest lands are within a half-mile of forest edges. That means almost no forests can really be considered wilderness."

Covering many ecosystems, from forests to savannahs to grasslands, the experiments combined to show a disturbing trend.

Fragmentation changes how ecosystems function, reduces the amounts of nutrients retained and the amount of carbon sequestered and has other deleterious effects.

Negative effects of fragmentation and help for the forest

"The initial effects were unsurprising," Haddad said. "But I was blown away by the fact that these negative effects became even more negative with time. Some results showed a 50 percent or higher decline in plant and animal species over an average of just 20 years.

"And the trajectory is still spiraling downward."

Haddad points to some possible ways of mitigating the effects of fragmentation: conserving and maintaining larger areas of habitat; using landscape corridors, or connected fragments that are effective in maintaining higher biodiversity and better ecosystem function; increasing agricultural efficiency; and focusing on urban design efficiencies.

"Ultimately, habitat fragmentation has harmful effects that will also hurt people," said Haddad.

"This study is a wake-up call to how much we're affecting ecosystems--including areas we think we're conserving."

-- Cheryl Dybas, NSF

TERMITES vs. DESERTS

FROM:  THE NATIONAL SCIENCE FOUNDATION
Dirt mounds made by termites in Africa, South America, Asia could prevent spread of deserts
Termites create oases of moisture, plant life
February 5, 2015

Termites might not top the list of humanity's favorite insects, but new research suggests that their large dirt mounds are crucial to stopping deserts from spreading into semi-arid ecosystems.

The results indicate that termite mounds could make these areas more resilient to climate change.

The findings could also inspire a change in how scientists determine the possible effects of climate change on ecosystems.

In the parched grasslands and savannas, or drylands, of Africa, South America and Asia, termite mounds store nutrients and moisture and via internal tunnels, allow water to better penetrate the soil.

As a result, vegetation flourishes on and near termite mounds in ecosystems that are otherwise vulnerable to desertification.

Researchers report in this week's issue of the journal Science that termites slow the spread of deserts into drylands by providing a moist refuge for vegetation on and around their mounds.

Drylands with termite mounds can survive on significantly less rain than those without termite mounds.

Not all termites are pests

"This study demonstrates that termite mounds create important refugia for plants and help to protect vast landscapes in Africa from the effects of drought," said Doug Levey, program director in the National Science Foundation's Division of Environmental Biology, which funded the research.

"Clearly," said Levey, "not all termites are pests."

The research was inspired by the fungus-growing termite species, Odontotermes, but the results apply to all types of termites that increase resource availability on or around their mounds.

Corresponding author Corina Tarnita, a Princeton University ecologist and evolutionary biologist, said that termite mounds also preserve seeds and plant life, which helps surrounding areas rebound faster once rainfall resumes.

"Because termites allow water to penetrate the soil better, plants grow on or near the mounds as if there were more rain," said Tarnita. "The vegetation on and around termite mounds persists longer and declines slower.

"Even when you get to harsh conditions where vegetation disappears from the mounds, re-vegetation is still easier. As long as the mounds are there the ecosystem has a better chance to recover."

The stages of desertification: Where termites fit in

In grasslands and savannas, five stages mark the transition to desert, each having a distinct pattern of plant growth.

The researchers found that these plant growth patterns exist on a much smaller scale than previously thought. Overlaying them is the pattern of termite mounds covered by dense vegetation.

The termite-mound pattern, however, looks deceptively similar to the last and most critical of the five stages that mark the transition of drylands to desert.

Vegetation patterns that might be interpreted as the onset of desertification could mean the opposite: that plants are persevering thanks to termite mounds.

Termite mounds help grassland plants persevere

Robert Pringle, an ecologist and evolutionary biologist at Princeton and co-author of the paper, said that the unexpected function of termites in savannas and grasslands suggests that ants, prairie dogs, gophers and other mound-building creatures could also have important roles in ecosystem health.

"This phenomenon and these patterned landscape features are common," Pringle said.

"Exactly what each type of animal does for vegetation is hard to know in advance. You'd have to get into a system and determine what is building the mounds and what the properties of the mounds are.

"I like to think of termites as linchpins of the ecosystem in more than one way. They increase the productivity of the system, but they also make it more stable and more resilient."

Termites: Linchpins of the ecosystem

A mathematical model developed for the work determines how these linchpins affect plant growth.

The scientists applied tools from physics and mathematical and numerical analysis to understand a biological phenomenon, said paper first author Juan Bonachela of Strathclyde University in Scotland.

The model allowed the researchers to apply small-scale data to understand how rainfall influences vegetation growth and persistence in the presence and absence of termites across an entire ecosystem.

"Similar studies would be extremely challenging to perform in the field and would require very long-term experiments," Bonachela said.

"Models such as this allow us to study the system with almost no constraint of time or space and explore a wide range of environmental conditions with a level of detail that can't be attained in the field."

Additional support for the research was provided by a Princeton Environmental Institute Grand Challenges grant, the National Geographic Society, the Andrew W. Mellon Foundation and a John Templeton Foundation Foundational Questions in Evolutionary Biology grant.

-NSF-
Media Contacts
Cheryl Dybas, NSF

NSF PRESENTS FINDINGS FROM PAPER ON LARGE ANIMALS AND EFFECTS ON TROPICAL FORESTS

FROM:  THE NATIONAL SCIENCE FOUNDATION 

  Fruits of the forest gone: Overhunting of large animals has catastrophic effects on trees

As the animals go, so go tropical forests

The elephant has long been an important spiritual, cultural and national symbol in Thailand. At the beginning of the 20th century, its numbers exceeded 100,000.

Today, those numbers have plunged to 2,000. Elephants, as well as other large, charismatic animals such as tigers, monkeys and civet cats, are under attack from hunters and poachers.

Overhunting of animals affects entire forest

While the loss of these animals is concerning for species conservation, now researchers at the University of Florida have shown that overhunting can have widespread effects on the forest itself.

Overhunting leads to the extinction of a dominant tree species, Miliusa horsfieldii, or the Miliusa beech, with likely cascading effects on other forest biota.

The scientists report their results in the current issue of the journal Proceedings of the Royal Society B.

Co-authors of the paper are Trevor Caughlin and Jeremy Lichstein of the University of Florida and Doug Levey, formerly of the University of Florida and now a program director in the National Science Foundation's Division of Environmental Biology.

Other co-authors are researchers at King Mongkut's University of Technology Thonburi in Thailand, Wageningen University in the Netherlands and the Royal Thai Forest Department.

Loss of one tree species has far-reaching implications

The ecologists show how vital large animals are to maintaining the biodiversity of tropical forests in Thailand.

The team looked at how these mammals contribute to moving seeds through the forest.

"It's not surprising that seed dispersers help trees get to new places," says Levey. "The effects of hunting can extend far beyond the hunted, threatening the overall health of the trees that make up the forest."

Adds Caughlin, "On the surface, it doesn't seem that seed dispersal would be important for tree populations. But seed dispersal has an effect over the whole life of a tree."

Animals critical to seed transport through the forest

The scientists looked at the growth and survival of trees that sprouted from parent trees and grew up in crowded environs, compared to trees from seeds that were widely transported across the forest by animals.

The information was supplemented with a dataset from the Thai Royal Forest Department that contains more than 15 years of data on trees.

The researchers then created a long-term simulation and ran it on the University of Florida's supercomputer, the HiPerGator.

"Having that computing power was very important," says Caughlin, "because we had to simulate the fate of millions of seeds."

The scientists discovered that trees that grow from seeds transported by now-overhunted animals are hardier and healthier.

"Our study is the first to quantify the decades-long effects of animal seed dispersal across the entire tree life cycle, from seeds to seedlings to adult trees," says Lichstein.

Probability of tree extinction increased tenfold

The results show that loss of animal seed-dispersers increases the probability of tree extinction by more than tenfold over a 100-year period.

"The entire ecosystem is at risk," says Caughlin.

"We hope the study will provide a boost for those trying to curb overhunting," he says, "and provide incentives to stop the wildlife trade."

-- Cheryl Dybas, NSF
-- Gigi Marino, University of Florida

SCIENTISTS FIND GOOD NEWS REGARDING MIDWESTERN LAKES

FROM:  NATIONAL SCIENCE FOUNDATION 

Clarity for lake researchers' water quality questions

Studies of trends in Midwestern lakes benefit from help of local residents
Scientists engaged in a study of long-term water quality trends in Midwestern lakes found some good news: little change in water clarity in more than 3,000 lakes.

Look deeper, and the research becomes something more: a chronicle of a new source of data for scientists, data from residents of towns and villages surrounding the lakes.

The results are published in a paper in the journal PLOS ONE.

The paper co-authors analyzed almost a quarter of a million observations taken over seven decades on 3,251 lakes in eight Midwestern states.

Enter local residents

But the researchers didn't collect those data. The observations came from lakefront homeowners, boaters, anglers and other interested members of the public wanting to know more about what's going on in "their" lakes.

Noah Lottig, a co-author of the paper and a scientist at the University of Wisconsin-Madison's Center for Limnology, says that ecologists are looking at big-picture issues--such as how changes in land use or climate affect ecosystems--at state, national and continental scales.

This time, the help of local residents was key to the findings.

"This study highlights research opportunities using data collected by citizens making important environmental measurements," says Elizabeth Blood, program director in the National Science Foundation's (NSF) Directorate for Biological Sciences, which funded the work through its MacroSystems Biology Program. "Their efforts provide scientists with data at space and time scales often not available by other means."

Water clarity from a Secchi disk reading--or tens of thousands of them

Lottig and freshwater scientists from across the United States combed through state agency records and online databases. The water clarity measurements they sought were taken by non-scientists using a circular, plate-sized instrument called a Secchi disk.

Used in the aquatic sciences since the mid-1800s, Secchi disks hang from a rope and are lowered into the water until their distinct black-and-white pattern disappears from view, a distance that marks the "Secchi depth."

Lake associations and other groups have used the disks for decades to document conditions in their respective waters.

Previous studies have shown that local residents' Secchi readings are nearly as accurate as scientists' measurements, says Lottig.

With a dataset covering more than 3,000 lakes and stretching back to the late 1930s, the team decided to ask questions about long-term change.

Before and after the Clean Water Act

The Clean Water Act provided a useful frame of reference. Signed into law in 1972, the act set water quality goals for all U.S. waters.

Thanks to the data collected by residents, Lottig's team had access to water clarity measurements for decades before and after the act came into effect.

Somewhere in that data, the researchers reasoned, they might detect a landscape-scale shift over time to clearer (often an indicator of cleaner) water.

While there was a slight one percent yearly increase in water clarity for the lakes, Lottig says, "most of the lakes are just chugging along, not changing much through time."

While some lakes improved, others did not. Taken as a whole, there was no major change in clarity at the landscape scale.

Lottig is part of the "Cross-Scale Interaction" or "CSI Limnology" project, an effort to collect global data on water chemistry and aquatic biology that will add needed context.

Townspeople weigh in

For Ken Fiske, collecting data has been well worth the effort.

In 1985, Fiske saw an announcement for volunteers for a new Wisconsin lake monitoring program. Fiske had been coming to northern Wisconsin from his home in Illinois for years and had recently bought property on the shoreline of Lake Adelaide.

"My interest was in finding out what the quality of water in Lake Adelaide was and seeing what we could do to maintain it," he says.

For the next several years, Fiske went on a monthly five-hour drive to Lake Adelaide to take measurements. Eventually, he found some neighbors to help. Some 30 years later, the group is still going strong.

"We've been doing it long enough that it makes the results meaningful," Fiske says.

Scientists are harnessing efforts like Fiske's to try to answer questions about not just one lake, but 3,251--or more--of them.

-- Cheryl Dybas, NSF
Investigators
Noah Lottig
Emily Stanley
Related Institutions/Organizations
University of Wisconsin-Madison

NSF ON ROCKY MOUNTAIN BARK BEETLES AND WATER QUALITY

Photo:  Rocky Mountains. Credit:  Wikimedia, Williams Jim, U.S. Fish and Wildlife Service. 

FROM:  NATIONAL SCIENCE FOUNDATION 

Earth Week: Bark beetles change Rocky Mountain stream flows, affect water quality

What happens when millions of dead trees, killed by beetles, no longer need water?

On Earth Week--and in fact, every week now--trees in mountains across the western United States are dying, thanks to an infestation of bark beetles that reproduce in the trees' inner bark.

Some species of the beetles, such as the mountain pine beetle, attack and kill live trees. Others live in dead, weakened or dying hosts.

In Colorado alone, the mountain pine beetle has caused the deaths of more than 3.4 million acres of pine trees.

What effect do all these dead trees have on stream flow and water quality? Plenty, according to new research findings reported this week.

Dead trees don't drink water

"The unprecedented tree deaths caused by these beetles provided a new approach to estimating the interaction of trees with the water cycle in mountain headwaters like those of the Colorado and Platte Rivers," says hydrologist Reed Maxwell of the Colorado School of Mines.

Maxwell and colleagues have published results of their study of beetle effects on stream flows in this week's issue of the journal Nature Climate Change.

As the trees die, they stop taking up water from the soil, known as transpiration. Transpiration is the process of water movement through a plant and its evaporation from leaves, stems and flowers.

The "unused" water then becomes part of the local groundwater and leads to increased water flows in nearby streams.

The research is funded by the National Science Foundation's (NSF) Water, Sustainability and Climate (WSC) Program. WSC is part of NSF's Science, Engineering and Education for Sustainability initiative.

"Large-scale tree death due to pine beetles has many negative effects," says Tom Torgersen of NSF's Directorate for Geosciences and lead WSC program director.

"This loss of trees increases groundwater flow and water availability, seemingly a positive," Torgersen says.

"The total effect, however, of the extensive tree death and increased water flow has to be evaluated for how much of an increase, when does such an increase occur, and what's the water quality of the resulting flow?"

The answers aren't always good ones.

Green means go, red means stop, even for trees

Under normal circumstances, green trees use shallow groundwater in late summer for transpiration.

Red- and gray-phase trees--those affected by beetle infestations--stop transpiring, leading to higher water tables and greater water availability for groundwater flow to streams.

The new results show that the fraction of late-summer groundwater flows from affected watersheds is about 30 percent higher after beetles have infested an area, compared with watersheds with less severe beetle attacks.

"Water budget analysis confirms that transpiration loss resulting from beetle kill can account for the increase in groundwater contributions to streams," write Maxwell and scientists Lindsay Bearup and John McCray of the Colorado School of Mines, and David Clow of the U.S. Geological Survey, in their paper.

Dead trees create changes in water quality

"Using 'fingerprints' of different water sources, defined by the sources' water chemistry, we found that a higher fraction of late-summer streamflow in affected watersheds comes from groundwater rather than surface flows," says Bearup.

"Increases in stream flow and groundwater levels are very hard to detect because of fluctuations from changes in climate and in topography. Our approach using water chemistry allows us to 'dissect' the water in streams and better understand its source."

With millions of dead trees, adds Maxwell, "we asked: What's the potential effect if the trees stop using water? Our findings not only identify this change, but quantify how much water trees use."

An important implication of the research, Bearup says, is that the change can alter water quality.

The new results, she says, help explain earlier work by Colorado School of Mines scientists. "That research found an unexpected spike in carcinogenic disinfection by-products in late summer in water treatment plants."

Where were those water treatment plants located? In bark beetle-infested watersheds.

-- Cheryl Dybas, NSF
Investigators
Reed Maxwell
Eric Dickenson
Jonathan Sharp
Alexis Navarre-Sitchler
Related Institutions/Organizations
Colorado School of Mines

SCIENTISTS STUDY SEED DISPERSAL

FROM:  NATIONAL SCIENCE FOUNDATION 
Seed dispersal study shows value of conservation corridors

Ecologists study how wind moves seeds through longleaf pines
Field ecologists go to great lengths to get data. Radio collars and automatic video cameras are among their tools for documenting the natural world.

So when a group of ecologists set out to see how wind moves seeds through isolated patches of habitat carved into a longleaf pine plantation, they came up with a novel way of addressing this question. They twisted colored yarn to create mock seeds that would drift with the wind much like native seeds.

The scientists discovered that both wind and the corridors between the patches of habitat matter to seed dispersal in the longleaf pine forest.

Their experimental "seeds" were dusted with fluorescent powder and inserted into custom-made boxes mounted on poles, then released as the scientists monitored local wind conditions.

That night, the field crew returned for a black-light treasure hunt, locating more than 80 percent of the fake seeds, which glowed under the ultraviolet light.

The paths of these glowing seeds were matched with output from a computer model to produce the first accurate picture of how wind moves seeds through corridors linking two patches of habitat.

The study results are published in a paper in this week's issue of the journal Proceedings of the National Academy of Sciences (PNAS).

Conservation biologists have long discussed building conservation corridors to link isolated patches of protected land.

"Understanding the conservation impact of corridors is at the cutting edge of conservation," says lead paper author Ellen Damschen, a zoologist at the University of Wisconsin-Madison.

Corridors are designed to improve conditions for uncommon native species living in separated habitats.

Small populations in these "islands" of habitat may be killed by storms or disease. They may lack genetic diversity and be prone to inbreeding. And they may be unable to reach new habitat.

"It makes intuitive sense that these connections could foster genetic and biological diversity," says Damschen. "But there has been little scientific evidence for if and how they work."

Most of the studies have involved animals, she adds, even though plants provide the basic energy and structure to land ecosystems.

Wind matters for the movement of seeds and whole organisms, Damschen says. "In many open habitats, more than one-third of plants are wind dispersed, but there are also insects, spiders, pathogens and fungi that move on the wind."

The experiment, supported by the National Science Foundation (NSF) and the U.S. Forest Service, began in 2000 with the creation of eight groups of patches at the Savannah River Site, a large holding of the U.S. Department of Energy. Each set of patches was built at a different orientation to prevailing winds.

"Relatively few researchers have investigated the effects of habitat configuration on wind-dispersed species," says Betsy Von Holle, a program director in NSF's Division of Environmental Biology, which funded the research. "This study demonstrates that influences on wind-dispersed species are more complex than previously thought."

A research group of meteorologists and ecologists found that corridors increased the movement of wind and of their glowing artificial seeds, echoing the results of a computer model developed by Gil Bohrer at The Ohio State University, a paper co-author.

And when Damschen and colleagues counted newly dispersed plants over the 12-year experiment, they found that a corridor linking two patches of land indeed promotes the diversity of plants dispersed by wind - especially if the corridor is oriented roughly parallel to the prevailing winds.

Both the data and the model showed that wind speeds up in certain areas of the patches, and that a strong vertical air movement is present.

"Uplift is important because the wind tends to be faster higher above the ground," Damschen says, "and uplift can lead to long-distance dispersal, which is significant for moving plants around the landscape."

That's why the study matters for conservation biology, Damschen says.

"We predicted that corridors in line with the dominant winds would move more species, and this is what we found. Wind alignment matters for species diversity in conservation areas."

The results are especially relevant to threatened Midwestern ecosystems like grasslands, prairies and savannas, where big bluestem and milkweed are two of many native plants that loft their seeds on the wind.

"In conservation science, it is often assumed that wind-dispersed seeds can go everywhere, but that's not true," Damschen says.

"Wind direction, and the shape of the habitat, control where these seeds go.

"While this adds another factor to consider in management of natural areas, the information is on the table so we can make better decisions about how to achieve management goals."

Other co-authors of the paper are: Dirk Baker of the University of Wisconsin-Madison; Ran Nathan of The Hebrew University of Jerusalem; John Orrock of the University of Wisconsin-Madison; Jay Turner of Washington University in St. Louis; Lars Brudvig of Michigan State University; Nick Haddad of North Carolina State University; Doug Levey of the University of Florida, Gainesville; and Joshua Tewksbury of the University of Washington.

-NSF-

BIODIVERSITY AND DISEASE

Credit:  CIA World Factbook.

FROM: NATIONAL SCIENCE FOUNDATION
Biodiversity Protects Against Disease, Scientists Find
The richer the assortment of amphibian species in a pond, the more protection that community of frogs, toads and salamanders has against a parasitic infection that can cause severe deformities, including the growth of extra legs.

The findings, published in a paper in this week's issue of the journal Nature, support the idea that greater biodiversity in large-scale ecosystems, such as forests or grasslands, may also provide greater protection against diseases, including those that affect humans.

A larger number of mammal species in an area may curb cases of Lyme disease, while a larger number of bird species may slow the spread of West Nile virus.

"How biodiversity affects the risk of infectious diseases, including those of humans and wildlife, has become an increasingly important question," said Pieter Johnson, an ecologist and evolutionary biologist at the University of Colorado Boulder, and the lead author of the paper.

"But as it turns out, solidly testing these links with realistic experiments has proven very challenging in most systems."

Researchers have struggled to design comprehensive studies that could illuminate the possible connection between disease transmission and the number of species living in complex ecosystems.

Part of the problem is the enormous number of organisms that may need to be sampled, and the vast areas over which those organisms may roam.

This study overcame that problem by studying smaller, easier-to-sample ecosystems, the scientists say.

"The research reaches the surprising conclusion that the entire set of species in a community affects susceptibility to disease," said Doug Levey, program director in the National Science Foundation (NSF)'s Division of Environmental Biology, which funded the research. "Biodiversity matters."

Johnson and colleagues visited hundreds of ponds in California, recording the types of amphibians living there as well as the number of snails infected by the pathogen Ribeiroia ondatrae.

Snails are an intermediate host used by the parasite during part of its life cycle.

"One of the great challenges in studying the diversity-disease link has been collecting data from enough replicate systems to differentiate the influence of diversity from background 'noise,'" Johnson said.

"By collecting data from hundreds of ponds and thousands of amphibian hosts, we were able to provide a rigorous test of this hypothesis, which has relevance to a wide range of disease systems."

The researchers buttressed field observations with laboratory tests designed to measure how prone to infection each amphibian species is, and by creating pond replicas using large plastic tubs stocked with tadpoles that were exposed to a known number of parasites.

All the experiments told the same story.

Greater biodiversity reduced the number of amphibian infections and the number of deformed frogs.

The scientists spent three years sampling 345 wetlands and recording malformations--which include missing, misshapen or extra sets of hind legs--caused by parasitic infections in 24,215 amphibians.

The results showed that ponds with half a dozen amphibian species had a 78 percent reduction in parasite transmission compared to ponds with just one amphibian species.

The reason for the decline in parasitic infections as biodiversity increases is likely related to the fact that ponds add amphibian species in a predictable pattern, with the first species to appear being the most prone to infection and the later species to appear being the least prone.

The researchers found that in a pond with just one type of amphibian, that amphibian was almost always the Pacific chorus frog, a creature that's able to rapidly reproduce and quickly colonize wetland habitats, but which is also especially vulnerable to infection and parasite-induced deformities.

On the other hand, the California tiger salamander was typically one of the last species to be added to a pond community--and also one of the most resistant to parasitic infection.

Therefore, in a pond with greater biodiversity, parasites have a higher chance of encountering an amphibian that is resistant to infection, lowering the overall success rate of transmission between infected snails and amphibians.

This same pattern--of less diverse communities being made up of species that are more susceptible to disease infection--may well play out in more complex ecosystems, Johnson said.

That's because species that disperse quickly across ecosystems appear to trade off the ability to quickly reproduce with the ability to develop disease resistance.

The recent study also reinforces the connection between deformed frogs and parasitic infection.

In the mid-1990s reports of frogs with extra, missing or misshapen legs skyrocketed, attracting widespread attention in the media and motivating scientists to try to figure out the cause.

Johnson was among the researchers who found evidence of a link between infection with Ribeiroia and frog deformities, though the apparent rise in reports of deformations, and its underlying cause, remained controversial.

While the new study has implications beyond parasitic infections in amphibians, it does not mean that an increase in biodiversity always results in a decrease in disease, Johnson said.

Other factors also affect rates of disease transmission.

For example, a large number of mosquitoes hatching in a particular year increases the risk of contracting West Nile virus, even if there has been an increase in the biodiversity of the bird population.

Birds act as "reservoir hosts" for West Nile virus, harboring the pathogen indefinitely with no ill effects, then passing on the pathogen.

"Our results indicate that higher diversity reduces the success of pathogens in moving between hosts," Johnson said.

"But if infection pressure is high, there will still be a significant risk of disease. Biodiversity will simply dampen transmission success."

Co-authors of the paper are Dan Preston and Katie Richgels of the University of Colorado Boulder, and Jason Hoverman of Purdue University.

In addition to NSF, the research was funded by the National Geographic Society and the David and Lucile Packard Foundation.

-NSF-