Image left: SERC scientist João Canning Clode observes a green porcelain crab in his laboratory at the Smithsonian Environmental Research Center.

But what happens to these fair-weather travelers during a severe cold snap, such as the one that occurred in January 2010 across much of the southeastern and eastern United States? To investigate, Smithsonian Environmental Research Center scientist João Canning Clode and colleagues at the Environmental Research Center in Edgewater, Md., tested the cold-water tolerances of invasive green porcelain crabs (Petrolisthes armatus) in their laboratory. Crabs were collected in Georgia and brought to the lab where they were subjected to one of three temperature treatments. The first was a control treatment of constant moderate winter temperature. The second was treatment in which the temperature was dropped to mimic the cold snap of January 2010, and the third treatment consisted of the extreme cold temperatures of a severe winter.

Canning-Clode and his colleagues found that most of the crabs in the control treatment survived (83%), but many of the crabs in the second cold treatment (61%) and all of the crabs in the third extreme cold treatment (100%) died. Crabs that survived cold treatment number two were sluggish, possibly making them more susceptible to predation and impacting their ability to feed, the scientists determined.

The scientists determined that prolonged exposure to cold temperatures also may compromise the green porcelain crab’s ability to overcome cumulative cold events, such as the two other record cold snaps that occurred in February and March of 2010.

Image right: A green porcelain crab (Photo by Juan Antonio Baeza)

The loss of more than 60% of their population during each cold period might explain the recent dramatic decline of the green porcelain crab in Georgia in 2010, suggesting that extreme cold spells may limit or prevent the northward spread of this invasive species.

Several climate models used to predict how species will react to climate change in the next 100 years have projected a continued decline of global biodiversity and increased spread of introduced species. Many of these models focus on temperature increases, but few have evaluated the impact of severe weather like cold snaps, Canning-Clode and his colleagues write in a paper on their study recently published at PLoS ONE.

For Canning Clode “the core message of this paper is that yes, climate change is happening, but cold is also part of this change. We believe these periodic cold events will limit the range expansion of Petrolisthes armatus as well as other Caribbean creep species” –Monaca Noble, SERC

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Image right: The Smithsonian’s Barro Colorado Island was the site of the first large-scale, long-term forest dyanmics plots. Now there are 42 forest dynamics plots worldwide that use the same methodology, the Smithsonian Institution Global Earth Observatory system managed by the Center for Tropical Forest Science. (Photo by Marcos Guerra)

“Air pollution is fertilizing tropical forests with one of the most important nutrients for growth,” said S. Joseph Wright, staff scientist at the Smithsonian Tropical Research Institute in Panama. “We compared nitrogen in leaves from dried specimens collected in 1968 with nitrogen in samples of new leaves collected in 2007. Leaf nitrogen concentration and the proportion of heavy to light nitrogen isotopes increased in the last 40 years, just as they did in another experiment when we applied fertilizer to the forest floor.”

Nitrogen is an element created in stars under high temperatures and pressures. Under normal conditions, it is a colorless, odorless gas that does not readily react with other substances. Air consists of more than 75% nitrogen. But nitrogen also plays a big role in life as an essential component of proteins. When nitrogen gas is zapped by lightning, or absorbed by soil bacteria called “nitrogen fixers,” it is converted into other “active” forms that can be used by animals and plants. Humans fix nitrogen by the Haber process, which converts nitrogen gas into ammonia—now a principal ingredient in fertilizers. Today, nitrogen fixation by humans has approximately doubled the amount of reactive nitrogen emitted.

Image left: The Smithsonian’s Barro Colorado Island was the site of the first large-scale, long-term forest dyanmics plots. Now there are 42 forest dynamics plots worldwide that use the same methodology, the Smithsonian Institution Global Earth Observatory system managed by the Center for Tropical Forest Science. (Photo by Marcos Guerra)

Nitrogen comes in two forms or isotopes: atoms that have the same number of protons but different numbers of neutrons. In the case of nitrogen, the isotopes are ¹⁴N and ¹⁵N, although only about one in 300 nitrogen atoms is the heavier form. Imagine nitrogen in the ecosystem like a bowl of popcorn. Normally the ratio of popped (light) to unpopped (heavy) kernels stays the same, but when someone starts to eat the popcorn, the lighter, popped kernels get used up first, increasing the ratio of heavy to light kernels (or ¹⁵N/¹⁴N in the case of the ecosystem). Light nitrogen is lost through nitrate leaching and as gases such as N2, and various forms of nitrous oxides or “noxides,” some of which can be important greenhouse gases. In the fertilization study in Panama, mentioned earlier, N₂O emissions were tripled.

“Tree rings provide a handy timeline for measuring changes in wood nitrogen content,” said Peter Hietz from the Institute of Botany at the University of Natural Resources and Life Sciences in Vienna, who faced down a tiger when sampling trees in a monsoon forest on the Thailand-Myanmar border. “We find that over the last century, there’s an increase in the heavier form of nitrogen over the lighter form, which tells us that there is more nitrogen going into this system and higher losses. We also got the same result in an earlier study of tree rings in Brazilian rainforests, so it looks like nitrogen fixed by humans now affects some of the most remote areas in the world.”

“The results have a number of important implications,” said Ben Turner, staff scientist at STRI. “The most obvious is for trees in the bean family (Fabaceae), a major group in tropical forests that fix their own nitrogen in association with soil bacteria. Increased nitrogen from outside could take away their competitive advantage and make them less common, changing the composition of tree communities.”

“There are also implications for global change models, which are beginning to include nitrogen availability as a factor affecting the response of plants to increasing atmospheric carbon dioxide concentrations,” said Turner. “Most models assume that higher nitrogen equals more plant growth, which would remove carbon from the atmosphere and offset future warming. However a challenge for the models is that there is no evidence that trees are growing faster in Panama, despite the long-term increases in nitrogen deposition and atmospheric carbon dioxide.”

Decades of atmospheric nitrogen deposition have caused major changes in the plants and soils of temperate forests in the U.S. and Europe. Whether tropical forests will face similar consequences is an important question for future research.

The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is a unit of the Smithsonian Institution. The Institute furthers the understanding of tropical nature and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation by increasing public awareness of the beauty and importance of tropical ecosystems. Website: www.stri.org.

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The dodo’s large size and inability to fly were adaptations that allowed this bird to survive some of the most hostile conditions and climactic events imaginable. Only in the 1600s did a force more deadly than extreme drought and volcanic eruptions lead to its extinction: humans.

Image right: Painting of a dodo head by Cornelis Saftleven. Done in 1638,  this painting may be one of the last illustrations made of a live dodo. (Image from Boijmans Museum, Rotterdam)

In a recent paper in the journal “The Holocene” a team of scientists detail the extreme conditions that caused the death of some 500,000 animals on Mauritius during the mid-Holocene at around 4000 years ago. The evidence is a thick bed of fossil bones on Mauritius that spans an area of about 5 acres—the site of a former freshwater lake bed. The fossil layer is dominated by the remains of thousands of dodos and giant tortoises, as well as many small reptiles and flying birds.

Image left: Dodo bone in a matrix of mud, seed and other fossils excavated in a dry lake bed on the Island of Mauritius. (Image copyright Kenneth Rijsdijk/Dodo Research Programme)

Using radiocarbon dating of the bones, oxygen isotope analysis of geologic features on Mauritius and nearby islands, and the study of the island’s water table, the scientists determined the animals died during an extreme drought that lasted several decades. “Dodos, tortoises, lizards and other animals gathered here because the lake was one of the few sites on the island with fresh water,” says Hanneke Meijer, an ornithologist at the Smithsonian’s National Museum of Natural History and one of the paper’s co-authors.

“It is evident that a lot of animals suffered and died during this period, and their populations were greatly reduced,” Meijer continues, “but no species, including the dodo, went extinct during this extreme drought.” Fossil evidence reveals that “all animals were still living and the island’s ecosystem was intact at the time humans arrived in the 1600s.”

Image right: The excavation site on the island of Mauritius where the remains of some 500,000 animals were found, victims of an extreme drought some 4,000 years ago. (Image copyright Mikel Rijsdijk/Dodo Research Programme)

The dodo was resilient, and perfectly adapted to the island’s habitat, Meijer explains. “The island had no predators or carnivores and the dodo had no need to flee, so it lost its ability to fly. It received a reputation as stupid because it did not flee from humans” and human-introduced predators after they arrived at the dodo’s home in the 1600s.

Today, Meijer says, the forest cover on Mauritius has been reduced by 98 percent with only a few patches of original forest remaining. Considerable resources have been directed to preserving the island’s few remaining endemic species, such as the Mauritian kestrel. (The island’s giant tortoises went extinct in the 1800s when Dutch trade ships filled their holds with these long-lived animals to use as fresh meat on long voyages to and from Indonesia. “Mauritius was a popular stop because it provided fresh water and lots of food,” Meijer says)

Image left: Researchers at the Mauritius Island excavation site sieving excavated mud for small bones, teeth and plant remains. (Image copyright Mikel Rijsdijk/Dodo Research Programme)

Should another extended drought occur similar to the mid-Holocene event, it is very likely the remaining endemic species on Mauritius would not survive as the environment is so degraded. “Even many of the native plant species in the few remaining forest patches would probably perish,” Meijer says.

“With modern climate change scientists are very interested in how island animals adapt, as their ability to move to less disturbed areas is limited,” Meijer explains. “It has always been thought that animals on islands are particularly sensitive to climate change.” In the case of the dodo and other species on Mauritias, this new study reveals an island population highly resilient to climate change.

The article “Mid-Holocene (4200 kyr BP) mass mortalities in Mauritius (Mascarenes): Insular vertebrates resilient to climatic extremes but vulnerable to human impact,” appeared recently in the scientific journal “The Holocene.” (Rijsdijk, K.F., Zinke, J., de Louw, P.G.B., Hume,J.P., van der Plicht, J., Hooghiemstra, H., Meijer, H.J.M., Vonhof, H.B., Porch, N., Florens, F.B.V., Baider, C., van Geel, B., Brinkkemper, J., Vernimmen, T. & Janoo, A., 2011. Mid-Holocene (4200 kyr BP) mass mortalities in Mauritius (Mascarenes): Insular vertebrates resilient to climatic extremes but vulnerable to human impact. The Holocene, doi:10.1177/0959683611405236)

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Images left and below: The variation in biodiversity from place to place, called beta diversity, are actually very similar as you move from the tropics to the poles when you account for the number of species present in the first place. (Photos by Christian Ziegler)

“The same ecological processes seem to be working worldwide. The difference is that tropical organisms have been accumulating for vast periods of time,” said Nathan J.B. Kraft, post-doctoral fellow at the University of British Colombia, who led the research team.

“This study shows how collecting data using the same methods at sites around the world, similar to what we do at the Center for Tropical Forest Science–Smithsonian Institution Global Earth Observatories Network, offers new insights into the processes that shape ecological communities,” said Comita, formerly a post-doctoral fellow at the National Center for Ecological Analysis and Synthesis, now an assistant professor at The Ohio State University. “We found that measurements of variation in biodiversity from place to place, called beta diversity, are actually very similar as you move from the tropics to the poles when you account for the number of species present in the first place.”

Forests in Canada and Europe may have much more in common with tropical rainforests than previously believed. “We see that biodiversity patterns can be explained not by current ecological processes, unfolding over one or two generations, but by much longer-term historical and geological events,” said Kraft, who will join the faculty at the University of Maryland next year.

“Fossils tell a similar story,” said STRI scientist, Aaron O’Dea, co-author, with Willem Renema and others, of a 2008 article in Science showing that marine biodiversity hotspots could be traced back to ancient areas of tectonic activity. “Geological history reveals that glaciations and mass extinctions have lasting effects on the structure of biological communities. It bears witness to the devastation that occurs when accumulated biodiversity is lost: a threat we are facing today.”

The team, which also included researchers from institutions in the U.S., Canada and New Zealand, was supported by the U.S. National Center for Ecological Analysis and Synthesis and the U.S. National Science Foundation.–Beth King, Smithsonian Tropical Research Institute

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The research was led by scientists from the Centre for Ecology and Hydrology and the University of Cambridge, UK. The results were published online today in the scientific journal “Nature Climate Change.”

Image right: Leaf litter around the buttress roots of a tropical tree at the study site in Panama.

The researchers used results from a six-year experiment in a rainforest at the Smithsonian Tropical Research Institute in Panama, to study how increases in litterfall–dead plant material such as leaves, bark and twigs which fall to the ground–might affect carbon storage in the soil. Their results show that extra litterfall triggers an effect called ‘priming’ where fresh carbon from plant litter provides much-needed energy to micro-organisms, which then stimulates the decomposition of carbon stored in the soil

Lead author Emma Sayer from the Smithsonian Tropical Research Institute and the Centre for Ecology and Hydrology said, “Most estimates of the carbon sequestration capacity of tropical forests are based on measurements of tree growth. Our study demonstrates that interactions between plants and soil can have a massive impact on carbon cycling. Models of climate change must take these feedbacks into account to predict future atmospheric carbon dioxide levels.”

Image left: Undergrowth showing leaf litter at the Smithsonian Tropical Research Institute study site. (Photos by Emma Sayer)

The study concludes that a large proportion of the carbon sequestered by greater tree growth in tropical forests could be lost from the soil. The researchers estimate that a 30% increase in litterfall could release about 0.6 tonnes of carbon per hectare from lowland tropical forest soils each year. This amount of carbon is greater than estimates of the climate-induced increase in forest biomass carbon in Amazonia over recent decades. Given the vast land surface area covered by tropical forests and the large amount of carbon stored in the soil, this could affect the global carbon balance

Tropical forests play an essential role in regulating the global carbon balance. Human activities have caused carbon dioxide levels to rise but it was thought that trees would respond to this by increasing their growth and taking up larger amounts of carbon. However, enhanced tree growth leads to more dead plant matter, especially leaf litter, returning to the forest floor and it is unclear what effect this has on the carbon cycle.

“Soils are thought to be a long-term store for carbon but we have shown that these stores could be diminished if elevated carbon dioxide levels and nitrogen deposition boost plant growth,” Sayer adds.

Co-author Edmund Tanner, from the University of Cambridge, said, “This priming effect essentially means that older, relatively stable soil carbon is being replaced by fresh carbon from dead plant matter, which is easily decomposed. We still don’t know what consequences this will have for carbon cycling in the long term.” –Source: Center for Ecology and Hydrology

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Image right: A wild hellbender captured and released during a recent survey in southwest Virginia. Click photo to enlarge.  (Photos by J.D. Kleopfer, Virginia Department of Game and Inland Fisheries).

Now, a new study of hellbenders by scientists at the Smithsonian Conservation Biology Institute will place these amphibians at the center of the conservation of Appalachian salamanders. The Appalachian region has the greatest diversity of salamanders in the world. Some 76 different salamander species live in this area, and most are found nowhere else in the world. With a warming trend of between 2 and 6 degrees Celsius predicted for the coming century, biologists are concerned about the future of these amphibians, many of which live in cool microclimates.

Image left: Kimberly Terrell of the Smithsonian and Bill Hopkins of the Department of Fish and Wildlife Conservation at Virginia Polytechnic Institute, snorkel for hellbenders during a recent survey in southwest Virginia.

To better understand how hellbenders will respond to global warming, scientists at the Conservation Biology Institute plan to monitor a population of hellbenders in laboratory tanks at the Reptile Discovery Center of the Smithsonian’s National Zoological Park in Washington, D.C. Conditions in the tanks will reflect the short-term temperature fluctuations, seasonal temperature variation, and the overall warming predicted for coming decades.

Scientists will closely follow the physiology of the hellbenders under these conditions to determine how warming effects them, if at all—be it stress, slowing of their metabolism or changes in their immune system.

Image right: Bill Hopkins swabs a wild hellbender held by Kimberly Terrell to test for the presence of the chytrid fungus. The animal was safely released.

“Global warming is considered the primary threat facing Appalachian salamanders,” says Kimberly Terrell, a researcher at the Center for Species Survival at the Conservation Biology Institute. “Yet there is almost no information regarding the physiological effects of temperature change in these species.”

A second part of the study will include a survey of wild hellbenders in streams in Tennessee, Virginia, West Virginia and Pennsylvania. Hellbender health and habitat data collected from these surveys—such as water temperature, pH, dissolved oxygen levels, pollutants—will be integrated with the laboratory data to determine how these factors might combine with warming to undermine hellbender fitness. The survey also will include tagging the animals and testing individuals for Batrachochytrium dendrobatidis (also known as Bd or the chytrid fungus), a devastating pathogen that has driven dozens of amphibian species to extinction. The ability of this fungus to cause disease in the eastern hellbender is unknown. The Smithsonian is partenering with the Virginia Department of Game and Inland Fisheries on the project research and surveys.

Image left: This cool mountain stream in southwest Virginia is prime habitat for the eastern hellbender.

Data from a previous health assessment survey of hellbenders, conducted from 2006 to 2009 by Barbara Wolfe, Director of Conservation Medicine at The Wilds (Cumberland, Ohio), also will be integrated into the study.

Since the 1970’s, hellbender populations have mysteriously declined in several portions of their range, Terrell explains. “By establishing a set of known constraints to adapting to climate change in these animals, our research can help determine the causes of recent declines, warn us of future declines in certain areas and help inform conservation management plans for all Appalachian salamanders,” Terrell says. “Hellbenders are an ideal model species for dozens of other Appalachian salamanders.” –John Barrat

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Image right: Cold temperatures usually restrict mangroves to the tropics and subtropics, but a warming climate is causing them to creep northward. (Smithsonian Institution photo)

Candy Feller, senior ecologist at the Smithsonian Environmental Research Center in Edgewater, Md., will lead an effort to track more than 100 miles of Florida mangrove forests that are encroaching on salt marshes to the north. Feller has been studying mangroves for almost 20 years in Florida, Panama, Belize and Australia. The new grant is one of 15 NASA-sponsored projects that will combine satellite data with field work to give scientists a bird’s-eye view of climate change.

Cold temperatures usually restrict mangroves to the tropics and subtropics, but a warming climate has empowered them to expand northward.

Image right: Candy Feller extracts nectar from the blossom of a Pelliciera tree in a mangrove forest in Panama. (Kennedy Warne photo)

Mangrove trees thrive in the tropics and subtropics near the ocean. Their roots often appear above ground, and they can grow to enormous heights, up to 45 meters in some locations. They start reproducing at a young age, so they can establish themselves in a community very quickly. However, mangrove trees also are very sensitive to cold, which in the past has kept them from moving very far north.

Only a couple degrees of latitude north of the Florida mangrove forests are the salt marshes, ecosystems populated by small, soft-stemmed plants that prefer a more temperate climate. These plants only sprout up in warm weather and burrow underground when it becomes cold. Because the two types of plants have such different structures, a mass migration of mangroves northward could impact everything in the salt marsh ecosystem, including carbon sequestration, nutrient flow and the kinds of organisms can survive there.

Image right: An aerial view of Mangal Cay in the western Caribbean – just one of many mangrove havens where Candy Feller has conducted research.

With less of a chill to hold back the mangroves, an overlap zone 120 miles long—from Cocoa Beach in the south to St. Augustine in the north—has emerged where mangroves have invaded salt marsh territory. Feller and her team will base their study in this zone. For the next four years, they plan to analyze 21 different sites in the overlap zone hoping to find out how long the invasion has been going on, how fast it is happening and–most importantly–how it is affecting the ecosystems where salt marshes once dominated.

In addition to SERC scientists John Parker and Richard Osman, Feller will be joined in the study by Dan Gruner of the University of Maryland and Wilfrid Rodriguez of the University of Rhode Island.

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Image right: Amanda Reynolds and Whitman Miller use superglue to attach oysters to a plastic plate.

In September 2010, SERC Ecologist Whitman Miller, Trace Element Lab scientist Fritz Riedel, research technician Amanda Reynolds and several volunteers used superglue to attach oyster spat to the plates. They then put the plates inside floating cages at three different study sites on the Chesapeake’s Rhode River:  a boat dock in Edgewater, a weir in an area known as Kirkpatrick Marsh, and a river basin just outside Kirkpatrick Marsh. Although the sites are relatively close together their water chemistry is different.

Image left: A plate of oysters that has been submerged at the dock in Edgewater for about one month.

Increased acidity caused by the ocean’s absorption of atmospheric CO₂ in coming years may have dire consequences for oysters and other shellfish. The scientists are using the pH of the estuary waters as a proxy for how much CO₂ is in the  water–a lower pH means more CO2 and a higher acidity.   Increased acidity means a lowering of the water’s pH level. When CO₂ dissolves in seawater it creates carbonic acid that is rapidly transformed into carbonate and bicarbonate ions in the water. Increased acidity tips the balance toward bicarbonate formation and away from carbonate. Less carbonate in the water means the oysters have less material with which to build their shells, causing their shells to grow more slowly, grow not at all, or even begin to dissolve.

“Estuarine and coastal ecosystems may be especially vulnerable to changes in water chemistry because their relative shallowness, reduced salinity and lower alkalinity makes them inherently less buffered to changes in pH than the open ocean,” Reynolds says. “For organisms to survive in these waters, they must be able to withstand dramatic changes in carbonate chemistry and thus pH on a daily basis.”

The scientists are tracking the growth and survivorship of the spat, as well as the water chemistry in their study site to learn what pH levels and how much variation in pH the Eastern oyster can endure.

Image right: Whitman Miller deploying cages with oysters at the Kirkpatrick Marsh weir. (Photos courtesy Amanda Reynolds)

Along with the chemical data collected so far, the team is periodically taking snapshots of the oysters on the plates to analyze their growth. So far the results have been visually impressive, Reynolds says. “Even without formal growth analyses it is clear that the oysters on the dock have grown much larger than their oyster brethren at the weir, with the oysters at the basin falling somewhere in between.”

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