Constantine Alexander's blog

Sea Shepherd Galapagos documentary

This upcoming Sea Shepherd film 'Sea Shepherd Galapagos' which will premiere in October 2012, documents the extensive work carried out by Sea Shepherd in protecting and defending the Galapagos Marine Reserve against illegal poaching.

 

 

 

Imperial eagle in the urban jungle - An EU LIFE Project

The LIFE+ project, ‘Save the Raptors’, which was carried out by the Bulgarian Society for the Protection of Birds, has recently launched a video on the Eastern imperial eagle (Aquila heliaca) and the communication of its conservation needs through contemporary art.

A giant 20 m graffiti artwork was created recently on the front wall of a public school at the very heart of Sofia, Bulgaria’s capital city, as part of a charitable initiative featuring four graffiti artists. The impressive mural tells the story of the globally endangered eagle species. Only 23 pairs of this majestic bird remain, and these are found in remote regions of Sakar and West Strandja in southeast Bulgaria.

With initiatives such as the one undertaken in co-operation with a school, the Bulgarian Society for the Protection of Birds is aiming to reach young audiences and to leave a long-lasting legacy for the LIFE+ ‘Save the Raptors Project’. The giant graffiti is visible to everyone who walks by the school building.

 

 

 

Ecological monitoring on bird populations in Europe re-evaluated

		This is the logo for the SCALES project.

Biodiversity and environmental monitoring is of crucial importance to diagnose changes in the environment and natural populations in order to provide conservation practice with relevant data and recommendations. The information from monitoring is required, for example, for the design and evaluation of biodiversity policies, conservation management, land use decisions, and environmental protection.

Birds are headline indicators of biodiversity due to their worldwide distribution and popularity. More than 600 bird monitoring programs are in place in Europe, resulting in huge investment of effort. Nearly 28,000 people have been involved in the 144 monitoring programs analyzed in the Nature Conservation paper, spending almost 80,000 person days per year. The evaluation was performed in SCALES, a large-scale integrated project funded by the 7th Framework Program (FP7) of the European Union.

At a dedicated SCALES symposium at the 3rd European Congress of Conservation Biology (ECCB) in Glasgow on 28th-31st of August 2012, the lead author Dr Dirk Schmeller from the CNRS, France and guest researcher at the Helmholtz Centre for Environmental Research - UFZ in Leipzig, Germany, commented: "Although popular among conservationists, bird-monitoring practices have never been characterized quantitatively. We undertook a focused questionnaire-based survey to objectively explore the strengths and weaknesses of the massive bird-monitoring effort in Europe. The results indicate a high potential for further improvements to bird monitoring in sampling design, data analysis and involvement of volunteers from the public".

"Variation in space and time can cause a significant deviation in the monitoring results, which may lead to incorrect conservation policy decisions", added Dr Klaus Henle from UFZ and coordinator of SCALES. "Therefore increasing awareness of the spatial or temporal scale at which monitoring has been performed can be of crucial importance!"

		The cover for the second issue of Nature Conservation.

To optimize the monitoring practices, the scientists have proposed a range of recommendations. For most monitoring programs, the best data type to be collected is quantitative (count) data, such as number of individuals, which provide an early warning for conservation and policy. Further, monitoring could optimize resource allocation between independent monitoring sites. Importantly, even low variation between sites or years can induce spurious conclusions; hence repetitive sampling of the same sites within a year should be the rule.

In case of limited manpower, Schmeller and colleagues recommend an increase in the number of monitoring samples, even at the expense of the size of each sample. Further, more collaborations between monitoring programs at different scales need to be established, so that the sampled data may be integrated and re-used.

Finally, monitoring coordinators have to make special efforts to attract volunteers. Coordinators need to keep in mind several important points: 1) the specific characters of the local community; 2) having a recruitment strategy for volunteers interested in monitoring; 3) maintaining good communication with the volunteers; 4) having low hierarchies and treat volunteers with respect, and 5) making links to other voluntary organizations to add value to the work. Schmeller adds: "There is no one clear recipe to recruit and keep volunteers, but what is important is to keep in mind that the volunteers sacrifice their spare time for monitoring activities, which are of interest to all society!"

Reference: Schmeller D, Henle K, Loyau A, Besnard A, Henry PY (2012) Bird-monitoring in Europe – a first overview of practices, motivations and aims. Nature Conservation 2: 41-57. doi: 10.3897/natureconservation.2.3644

SCALES (2009) stands for "Securing the Conservation of biodiversity across Administrative Levels and spatial, temporal, and Ecological Scales" and is a European research project. Financed by the 7th EU framework programme for research and development (FP7), SCALES seeks ways to better integrate the issue of scale into policy and decision-making and biodiversity management in the EU.

Contact: Dr. Dirk Schmeller
dirk@die-schmellers.de
Pensoft Publishers

 

 

New Nature study illuminates 55 million years of the carbon cycle and climate history

The JOIDES Resolution

A study in the August 30 issue of Nature provides, in unprecedented detail, the history of a crucial indicator of the relationship between the carbon cycle and climate processes over the past 55 million years. Over this time period, when the Earth is known to have transitioned from "hothouse" to "icehouse" conditions, the oceans also experienced a dramatic shift in the carbonate compensation depth, or CCD. Defined as the depth below which carbonate minerals (such as calcite) dissolve completely, the CCD is known to fluctuate over time – it shallows during warm periods, and deepens when ice age conditions prevail. Now, however, scientists have a detailed and quantifiable record of just how much the CCD has shifted during recent geological history.

The study, which relies on seafloor sediment cores collected during a pair of 2009 expeditions on board the JOIDES Resolution, demonstrates that 55 million years ago, the CCD of the Pacific Ocean sat at an average of about two miles (3.3-3.6 km) below the sea surface. As the Earth cooled, however, the CCD sank – reaching its deepest point of almost three miles (4.8 km) between 13 and 11 million years ago. Today, the Pacific's CCD sits just less than three miles (4.5 km) deep, and is thought to be on the rise as a result of modern, human-induced climate change.

"Long-term change in CCD and changes in Earth's atmospheric carbon dioxide concentration both result from shifts in how carbon is cycled by earth processes," says study co-author Mitchell Lyle, a geoscientist at Texas A&M University who co-led the second of the two expeditions. "Adding geologic reserves of carbon into the oceans and atmosphere – by burning coal or petroleum, for example – causes oceans to become more acidic and causes the atmosphere and oceans to warm. This new CCD record is an important step toward understanding how the carbon system balances out over long time frames."

The Pacific Ocean has remained the largest ocean on Earth for millions of years. Today, it covers one third of the planet's surface, and its biologically productive equatorial region plays a very important role in the global carbon cycle and long-term climate patterns. Over four months, the drilling vessel JOIDES Resolution – operated by the U.S. Implementing Organization on behalf of the National Science Foundation (NSF) and the Integrated Ocean Drilling Program (IODP) – drilled nearly four miles of core samples at eight different locations across the center of the Pacific basin.

"We often discuss global warming induced by man-made carbon dioxide. However, on geological timescales of millions of years, other processes determine the carbon cycle," says lead author Heiko Pälike, a geoscientist at the University of Bremen who co-led the first expedition. Volcanoes are a major natural source of atmospheric carbon dioxide, while the weathering of carbonate rocks can remove the gas from the atmosphere. "The overall balance of these processes is reflected in the CCD," explains Pälike.

In the Nature study, Pälike, Lyle and their co-authors demonstrate that, in the equatorial Pacific, the CCD did not follow a one-way path to the depths as the planet cooled down. Rather, the data reveals five intervals in the "greenhouse" world (prior to 33 million years ago) during which the CCD fluctuated upwards and downwards in a range between 650 and 3,000 feet (200-900 meters), and at least four more major excursions in the last 20 million years. "These events, which often mirror warming and cooling phases, persisted between 250,000 and one million years," Pälike explains. They resulted from minor differences between how much calcium was added to the oceans by weathering versus how much carbon dioxide was added to the ocean-atmosphere system by volcanic eruptions. The cycling of carbon between the sea surface and deep ocean further complicated the situation.

"Understanding the processes that caused these CCD excursions will provide important new insights about how the carbon cycle and climate are linked," Lyle says. "And, they will help us better understand how and when the current spike in atmospheric carbon dioxide will eventually level out."

The paper, titled "A Cenozoic record of the equatorial Pacific carbonate compensation depth," appears in the August 30, 2012 issue of the journal Nature. (doi:10.1038/nature11360)

Contact: Keith Randall
keith-randall@tamu.edu
979-845-4644
Texas A&M University

 

 

Climate change stories from the abyss

A team of scientists including those from the University of Southampton have shed new light on the world's history of climate change.

The Pacific Ocean has remained the largest of all oceans on the planet for many million years. It covers one third of the Earth's surface and has a mean depth of 4.2 km. Its biologically productive equatorial regions play an important role particularly to the global carbon cycle and long-term climate development.

During a four-month expedition of the Integrated Ocean Drilling Programme (IODP) on board the US drilling vessel JOIDES Resolution an international team of more than 100 scientists and technicians recovered 6.3 kilometers of sediment cores from water depths between 4.3 and 5.1 km and drilled 6.3 km of sediment cores at eight locations.

The cores offered an excellent archive of Earth's history and showed how global climate development during the past 55 million years is mirrored and influenced by geochemical processes deep within the ocean.

The findings are published in the latest edition of Nature.

Professor Heiko Pälike, of the University of Southampton and National Oceanography Centre, Southampton was co-chief scientist of the cruise and lead author of the Nature study.

He explains: "Nowadays we often discuss global warming induced by man-made carbon dioxide. However, on geological timescales of millions of years other processes determine the carbon cycle."

Volcanoes are one major source of carbon dioxide input to the atmosphere. On the other hand the greenhouse gas is removed by weathering of rocks made up of carbonate.

"The overall balance of these processes is reflected in the deep ocean's carbonate compensation depth, the CCD," the MARUM scientist continues.

"This invisible surface is defined as the depth in the oceans at which the mineral calcite is dissolved. Hardly any biological remains made from carbonate below the CCD, for example chalk and microscopic plankton, are preserved. Instead the sediment that consists mostly of clay and plankton remains made from silica.

"The interesting point in our study is that the carbonate boundary is fluctuating over time. It shallows during periods of warm climate and normally deepens when ice age conditions prevail."

In the study, Professor Pälike and co-workers demonstrate that in the equatorial Pacific the CCD was at 3.3 to 3.6km 55 million years ago. Between 52 and 47 million years ago, when very warm climate conditions prevailed, the CCD leveled up to 3 km. 34 million years ago, when the Earth slowly but steadily cooled and the first ice domes formed in Antarctica the CCD went down too. 10.5 million years ago it reached 4.8 km.

The cores drilled during the expedition strikingly demonstrate that the interplay of climate development and carbon cycle was not a one-way street at all.

"From 46 to 34 million years ago, when Earth turned into a permanent icehouse, our record reveals five intervals during which the CCD fluctuated upwards and downwards in the range of 200 and 900 metres," Professor Pälike says. "These events, that often mirror warming and cooling phases, persisted between 250,000 and one million years."

Similar episodes were registered in the sediment cores for later parts of the Earth's history. 18.5 million years ago the CCD moved upward about 600 metres – only to sink down to 4.7 km 2.5 million years later. Today, the Pacific carbonate compensation depth is at 4.5 km.

Contact: Becky Attwood
r.attwood@soton.ac.uk
44-023-805-95457
University of Southampton

 

 

Study suggests large methane reservoirs beneath Antarctic ice sheet

Antarctic Ice Sheet. Credit: NASA/GRACE team/DLR/Ben Holt Sr.

The Antarctic Ice Sheet could be an overlooked but important source of methane, a potent greenhouse gas, according to a report in the August 30 issue of Nature by an international team of scientists.

The new study demonstrates that old organic matter in sedimentary basins located beneath the Antarctic Ice Sheet may have been converted to methane by micro-organisms living under oxygen-deprived conditions. The methane could be released to the atmosphere if the ice sheet shrinks and exposes these old sedimentary basins.

Coauthor Slawek Tulaczyk, a professor of Earth and planetary sciences at UC Santa Cruz, said the project got its start five years ago in discussions with first author Jemma Wadham at the University of Bristol School of Geographical Sciences, where Tulaczyk was on sabbatical.

"It is easy to forget that before 35 million years ago, when the current period of Antarctic glaciations started, this continent was teeming with life," Tulaczyk said. "Some of the organic material produced by this life became trapped in sediments, which then were cut off from the rest of the world when the ice sheet grew. Our modeling shows that over millions of years, microbes may have turned this old organic carbon into methane."

The science team estimated that 50 percent of the West Antarctic Ice Sheet (1 million square kilometers) and 25 percent of the East Antarctic Ice Sheet (2.5 million square kilometers) overlies pre-glacial sedimentary basins containing about 21,000 billion metric tons of organic carbon.

"This is an immense amount of organic carbon, more than ten times the size of carbon stocks in northern permafrost regions," Wadham said. "Our laboratory experiments tell us that these sub-ice environments are also biologically active, meaning that this organic carbon is probably being metabolized to carbon dioxide and methane gas by microbes."

The researchers numerically simulated the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model. They found that sub-ice conditions favor the accumulation of methane hydrate (that is, methane trapped within a structure of water molecules, forming a solid similar to regular ice).

They also calculated that the potential amount of methane hydrate and free methane gas beneath the Antarctic Ice Sheet could be up to 4 billion metric tons, a similar order of magnitude to some estimates made for Arctic permafrost. The predicted shallow depth of these potential reserves also makes them more susceptible to climate forcing than other methane hydrate reserves on Earth.

Coauthor Sandra Arndt, a NERC fellow at the University of Bristol, who conducted the numerical modeling, said, "It's not surprising that you might expect to find significant amounts of methane hydrate trapped beneath the ice sheet. Just like in sub-seafloor sediments, it is cold and pressures are high, which are important conditions for methane hydrate formation."

If substantial methane hydrate and gas are present beneath the Antarctic Ice Sheet, methane release during episodes of ice-sheet collapse could act as a positive feedback on global climate change during past and future ice-sheet retreat.

"Our study highlights the need for continued scientific exploration of remote sub-ice environments in Antarctica, because they may have far greater impact on Earth's climate system than we have appreciated in the past," Tulaczyk said.

This research is a collaborative venture between the University of Bristol (UK), The University of California, Santa Cruz (USA), The University of Alberta, Edmonton, and the University of Utrecht (The Netherlands). It was funded principally by the Natural Environment Research Council (UK), the Leverhulme Trust (UK) with additional funds from the National Science Foundation (USA), the Natural Science and Engineering Research Council of Canada and the Netherlands Organization for Scientific Research (NWO).

Contact: Tim Stephens
stephens@ucsc.edu
831-459-2495
University of California - Santa Cruz

 

 

URI oceanographers find there is one-third less life on Earth

New estimate represents fewer subseafloor microbes

Credit: NASA

Estimates of the total mass of all life on Earth should be reduced by about one third, based on the results of a study by a team of scientists at the University of Rhode Island's Graduate School of Oceanography and colleagues in Germany.

The research was published this week in the Proceedings of the National Academy of Science.

According to previous estimates, about one thousand billion tons of carbon is stored in living organisms, of which 30 percent is in single-cell microbes in the ocean floor and 55 percent reside in land plants. The researchers have now revised the number downward. Instead of 300 billion tons of carbon in subseafloor microbes, they estimate these organisms contain only about 4 billion tons. This reduces the total amount of carbon stored in living organisms by about one-third.

"Previous estimates of microbial biomass in the ocean sediments were hindered by a limited number of sample locations preferentially located in near-shore, high-productivity regions," explained Rob Pockalny, URI associate marine research scientist. "With support from the National Science Foundation, we were able to obtain samples from the middle of the Pacific Ocean in some of the lowest productivity regions in the ocean."

Earlier estimates were based on drill cores that were taken close to shore or in very nutrient-rich areas.

"About half of the world's ocean is extremely nutrient-poor. For the last 10 years it was already suspected that subseafloor biomass was overestimated," explained Jens Kallmeyer at the University of Potsdam, Germany. "Unfortunately there were no data to prove it."

So the research team, which also included URI oceanographers David Smith and Steven D'Hondt, collected sediment cores from areas that were far away from any coasts and islands. The six-year work showed that there were up to 100,000 times fewer cells in sediments from open-ocean areas, which are dubbed "deserts of the sea" due to their extreme nutrient depletion, than in coastal sediments.

Pockalny said that the scientists were able to make predictions about microbial distributions in some regions of the world's oceans based on simple parameters like sediment accumulation rate and distance from shore.

With this new data, the scientists recalculated the total biomass in marine sediments and found drastically lower values. The new findings contribute to a better picture of the distribution of living biomass on Earth.

Despite of the high logistical and financial efforts for marine drilling operations, there are more data about the abundance of living biomass in the sea floor than about their abundance on land.

Contact: Todd McLeish
tmcleish@uri.edu
401-874-7892
University of Rhode Island

 

 

Soaking up the Sun

Drexel-Penn partnership to make more efficient dye-sensitized solar panels

 

Solar panels, like those commonly perched atop house roofs or in sun-drenched fields, quietly harvesting the sun's radiant energy, are one of the standard-bearers of the green energy movement. But could they be better – more efficient, durable and affordable? That's what engineers from Drexel University and The University of Pennsylvania are trying to find out, with the aid of a little nanotechnology and a lot of mathematical modeling.

A three-year grant from the National Science Foundation has set the team on a track to explore ways to make new photoelectric cells more efficient, durable and affordable. The group is examining "dye-sensitized" solar panels, which capture radiation via photosensitive dye and convert it into electricity. Their goal: streamline the electron transfer process inside the solar panels to make them more efficient at converting the radiation into electricity.

Dye-sensitized solar panels currently convert about 11 to 12 percent of the sunlight that hits them into electricity. The researchers are pushing to make these panels at least as efficient as their silicon counterparts, which currently convert about twice as much radiation as the dye-sensitized panels.

Despite this relative inefficiency, dye-sensitized panels have many advantages over silicon cells. Among the advantages of dye-sensitized solar cells are low cost, ease of manufacturing and construction from stable and abundant resource materials. Also, the durability of the dye-sensitized panels, combined with their ability to absorb more sunlight per surface area than standard silicon-based solar panels, make them attractive for mainstream use. There is also the potential to make dye-sensitized cells flexible, which would open them to a variety of new applications that are not options for the more rigid silicon panels. Due to the lagging energy conversion rate of dye-sensitized cells, however, they are not as widely used as silicon panels. But with help from the group's research, this obstacle could soon be surmounted.

"Our ultimate goal is to design and test a highly efficient dye-sensitized solar cell array through computational optimal design, synthesis and integration," said Dr. Masoud Soroush, the project's lead principal investigator from Drexel.

The primary strategies put forth by the group involve organizing the erratic movement of radiation-excited, or "photogenerated," electrons into a more orderly flow and maintaining that flow through the interior of solar cell by refining the material in its electrolyte substrate.

"We are seeking the combination of electrolyte and electrode materials and cell design that provide the highest power conversion efficiency," Soroush said. "The final design should have minimum losses in electrical conduction within the photoanode and electrolyte of the cell."

Making a Path

At present, the process of energy collection and disbursal in a solar cell functions something like a frenetic fire drill. Solar radiation hits the photosensitive dye, which excites the electrons and sends them in an electrically charged frenzy through the field of nanoparticles comprising the electrode and finally out into the rest of the circuit.

The engineers are attempting to direct this rapid exodus of photogenerated electrons by inserting carbon nanotubes, tiny cylindrical graphite-carbon tubes that measure less than 10 nanometers in diameter, to act as corrals for their escape.

"In order for a solar cell to generate an electric current, the photogenerated electrons in the photoanode have to travel through the network of titanium dioxide nanoparticles and they encounter many boundaries between nanoparticles during the transport," said Dr. Daeyeon Lee, the project's principal investigator from the University of Pennsylvania. "Due to this random transit path for the electrons, a large fraction of them are lost in the nanoparticle network before they reach the indium tin oxide glass, thus failing to generate electric power."

According to Lee, carbon nanotubes provide uninterrupted pathways for electrons, while also preventing the loss of photogenerated electrons in transit from the solar cell into the exterior circuit. With the addition of the nanotubes, the overall charge collection efficiency of the solar cell is expected to increase.

Completing the Loop

The second part of the research aims to replace the electrolyte solution that separates the electrodes inside the solar cell with a more effective polymer substance. The electrolyte serves as an internal pathway for negatively charged ions to carry electrons from the cathode (negative electrode) to the anode (positive electrode), thus completing the electrical circuit. Currently, dye-sensitized solar cells use a liquid electrolyte because it is easier for the sponge-like, porous electrode to soak up the liquid for maximum contact. It is difficult, however, to seal in the liquid, leading to leakage problems. In addition, the transit of the negatively charged species through a liquid is much less efficient than through a polymer, according to the group.

"Replacing the liquid electrolyte with a polymer will help us make a more efficient solar cell. Unlike the liquid, the polymer will not leak out of the cell and opens the door for making a flexible solar cell," said Dr. Kenneth Lau, the project's co-principal investigator from Drexel. "The solid polymer is also going to reduce some of the major conversion losses in the cell by closing doors that lead to electron loss that takes place with using a runny liquid."

Lau's group has also devised a method to get the polymer into the sponge-like electrode –a challenge which is one of the main reasons for the use of a liquid electrolyte substrate in current solar cells. "Simply put, we have invented a method for directly making the polymer inside the sponge-like electrode, rather than figuring a way to squeeze an already-made solid polymer into the electrode," Lau said.

Modeling the Cell

The variables in the research, including nanotube placement and polymer composition, could make prototype manufacturing and testing a pricey and time-consuming endeavor. But with the help of a computational material design program, developed by Soroush, the team will avail itself of rapid mathematical modeling to determine the most effective combination of materials and layout. Soroush's program is unique to Drexel's research in dye-sensitized solar cells and gives the team a distinct advantage in reaching its goal.

"Our predictive solid-state dye-sensitized solar cell model will allow us to establish important relations between cell performance and cell design and its material parameters," Soroush said. "We will then use the predictive model to evaluate the cell performance over the entire cell design parameter space. By doing this we will be able to systematically search for and arrive at the design specifications that will optimize the cell's operation."

Contact: Britt Faulstick
bef29@drexel.edu
215-895-2617
Drexel University

 

 

Climate change could increase levels of avian influenza in wild birds

Rising sea levels, melting glaciers, more intense rainstorms and more frequent heat waves are among the planetary woes that may come to mind when climate change is mentioned. Now, two University of Michigan researchers say an increased risk of avian influenza transmission in wild birds can be added to the list.

Population ecologists Pejman Rohani and Victoria Brown used a mathematical model to explore the consequences of altered interactions between an important species of migratory shorebird and horseshoe crabs at Delaware Bay as a result of climate change.

They found that climate change could upset the carefully choreographed interactions between ruddy turnstone shorebirds and the horseshoe crabs that provide the bulk of their food during the birds' annual stopover at Delaware Bay, a major estuary of the Delaware River bordered by New Jersey to the north and Delaware to the south.

Climate change-caused disruptions to the well-timed interplay between the birds and crabs could lead to an increase in the avian influenza infection rate among ruddy turnstones and resident ducks of Delaware Bay, the researchers found. Because Delaware Bay is a crossroads for many bird species traveling between continents, an increase in the avian infection rate there could conceivably help spread novel subtypes of the influenza virus among North American wild bird populations, according to Rohani and Brown.

Their findings were published online Aug. 29 in the journal Biology Letters.

"We're not suggesting that our findings necessarily indicate an increased risk to human health," said Rohani, a professor of ecology and evolutionary biology, a professor of complex systems and a professor of epidemiology at the School of Public Health.

"But every single pandemic influenza virus that has been studied has included gene segments from avian influenza viruses. So from that perspective, understanding avian influenza transmission in its natural reservoir is, in itself, very important."

Avian influenza refers to infection with bird flu Type A viruses. Those viruses occur naturally among wild aquatic birds worldwide and can infect domestic poultry and other bird and animal species.

Avian flu viruses do not normally infect humans. However, sporadic human infections with avian flu viruses have occurred. Since 2003, for example, more than 600 cases—including more than 300 deaths—of human infection with highly pathogenic avian influenza A H5N1 have been reported worldwide, according to the World Health Organization.

Delaware Bay, which hosts many resident bird species as well as the hundreds of thousands of migratory birds that gather to feed on horseshoe crab eggs, is known as a hot spot for avian influenza virus. Infection levels in ruddy turnstones, which stop at Delaware Bay each May during their northbound migration to breeding grounds in the Arctic after wintering in South America, have been found to be exceptionally high.

The birds time their arrival at Delaware Bay to coincide with the availability of the horseshoe crab eggs. Brown and Rohani wondered what would happen to influenza levels in Delaware Bay birds if climate change altered the timing of the ruddy turnstone's migratory flight to Delaware Bay or affected the timing of horseshoe crab spawning.

Their mathematical model looked at virus infection rates in ruddy turnstones and two species of duck—mallards, which winter at the bay, and American black ducks, which live there year-round.

The researchers found that if ruddy turnstones reached Delaware Bay either several weeks earlier or later than their current May arrival date, influenza infection rates in the species increased significantly, driving up the infection rates—also called prevalence levels—in the resident ducks as well.

"If the ruddy turnstones arrive either earlier or later than they do now, then their arrival coincides with higher viral prevalence in the resident ducks," said Brown, a postdoctoral research fellow in the Department of Ecology and Evolutionary Biology and the Center for the Study of Complex Systems. "And because these birds are interacting with a greater number of infected resident ducks, prevalence levels in ruddy turnstones are boosted.

"There's a feedback mechanism at work as well. Higher prevalence levels in the ruddy turnstones may, in turn, impact the prevalence levels in the resident ducks, driving them even higher."

If the timing of the horseshoe crab spawning season at Delaware Bay changed significantly due to climate change, ruddy turnstone populations would drop significantly due to a loss of food, and the influenza infection rate would decrease sharply as well, the researchers found.

Delaware Bay was declared a site of hemispheric importance by the Western Hemisphere Shorebird Reserve Network in 1986. Sites of hemispheric importance act as staging, nesting or breeding grounds for at least 500,000 shorebirds annually, or at least 30 percent of the biogeographic population of any species.

Contact: Laura Lessnau
llessnau@umich.edu
734-647-1851
University of Michigan

 

 

 

Stanford researchers discover the 'anternet'

Pogonomyrmex barbatus. Credit: Joseph Berge

On the surface, ants and the Internet don't seem to have much in common. But two Stanford researchers have discovered that a species of harvester ants determine how many foragers to send out of the nest in much the same way that Internet protocols discover how much bandwidth is available for the transfer of data. The researchers are calling it the "anternet."

Deborah Gordon, a biology professor at Stanford, has been studying ants for more than 20 years. When she figured out how the harvester ant colonies she had been observing in Arizona decided when to send out more ants to get food, she called across campus to Balaji Prabhakar, a professor of computer science at Stanford and an expert on how files are transferred on a computer network. At first he didn't see any overlap between his and Gordon's work, but inspiration would soon strike.

"The next day it occurred to me, 'Oh wait, this is almost the same as how [Internet] protocols discover how much bandwidth is available for transferring a file!'" Prabhakar said. "The algorithm the ants were using to discover how much food there is available is essentially the same as that used in the Transmission Control Protocol."

Transmission Control Protocol, or TCP, is an algorithm that manages data congestion on the Internet, and as such was integral in allowing the early web to scale up from a few dozen nodes to the billions in use today. Here's how it works: As a source, A, transfers a file to a destination, B, the file is broken into numbered packets. When B receives each packet, it sends an acknowledgment, or an ack, to A, that the packet arrived.

This feedback loop allows TCP to run congestion avoidance: If acks return at a slower rate than the data was sent out, that indicates that there is little bandwidth available, and the source throttles data transmission down accordingly. If acks return quickly, the source boosts its transmission speed. The process determines how much bandwidth is available and throttles data transmission accordingly.

It turns out that harvester ants (Pogonomyrmex barbatus) behave nearly the same way when searching for food. Gordon has found that the rate at which harvester ants – which forage for seeds as individuals – leave the nest to search for food corresponds to food availability.

A forager won't return to the nest until it finds food. If seeds are plentiful, foragers return faster, and more ants leave the nest to forage. If, however, ants begin returning empty handed, the search is slowed, and perhaps called off.

Prabhakar wrote an ant algorithm to predict foraging behavior depending on the amount of food – i.e., bandwidth – available. Gordon's experiments manipulate the rate of forager return. Working with Stanford student Katie Dektar, they found that the TCP-influenced algorithm almost exactly matched the ant behavior found in Gordon's experiments.

"Ants have discovered an algorithm that we know well, and they've been doing it for millions of years," Prabhakar said.

They also found that the ants followed two other phases of TCP. One phase is known as slow start, which describes how a source sends out a large wave of packets at the beginning of a transmission to gauge bandwidth; similarly, when the harvester ants begin foraging, they send out foragers to scope out food availability before scaling up or down the rate of outgoing foragers.

Another protocol, called time-out, occurs when a data transfer link breaks or is disrupted, and the source stops sending packets. Similarly, when foragers are prevented from returning to the nest for more than 20 minutes, no more foragers leave the nest.

Prabhakar said that had this discovery been made in the 1970s, before TCP was written, harvester ants very well could have influenced the design of the Internet.

Gordon thinks that scientists have just scratched the surface for how ant colony behavior could help us in the design of networked systems.

There are 11,000 species of ants, living in every habitat and dealing with every type of ecological problem, Gordon said. "Ants have evolved ways of doing things that we haven't thought up, but could apply in computer systems. Computationally speaking, each ant has limited capabilities, but the collective can perform complex tasks.

"So ant algorithms have to be simple, distributed and scalable – the very qualities that we need in large engineered distributed systems," she said. "I think as we start understanding more about how species of ants regulate their behavior, we'll find many more useful applications for network algorithms."

The work is published in the Aug. 23 issue of PLoS Computational Biology.

Contact: Bjorn Carey, Stanford News Service
bccarey@stanford.edu
650-725-1944
Stanford University