Showing posts with label declining amphibians. Show all posts
Showing posts with label declining amphibians. Show all posts

Friday, October 28, 2011

Land Animals & Ecosystems Decimated During the Permian Extinction


To the left. Lystrosaurs escaped the destruction of the Permian catastrophe as did the meter high spore-tree Pleuromeia it is feeding on. Illustration credit: Victor Leshky.

PROVIDENCE, R.I. [Brown University] — The cataclysmic events that marked the end of the Permian Period some 252 million years ago were a watershed moment in the history of life on Earth. As much as 90 percent of ocean organisms were extinguished, ushering in a new order of marine species, some of which we still see today. But while land dwellers certainly sustained major losses, the extent of extinction and the reshuffling afterward were less clear.

In a paper published in the journal Proceedings of the Royal Society B, researchers at Brown University and the University of Utah undertook an exhaustive specimen-by-specimen analysis to confirm that land-based vertebrates suffered catastrophic losses as the Permian drew to a close. From the ashes, the survivors, a handful of genera labeled "disaster taxa," were free to roam more or less unimpeded, with few competitors in their respective ecological niches. This lack of competition, the researchers write, caused vicious boom-and-bust cycles in the ecosystems, as external forces wreaked magnified havoc on the tenuous links in the food web. As a result, the scientists conclude from the fossil record that terrestrial ecosystems took up to 8 million years to rebound fully from the mass extinction through incremental evolution and speciation.

"It means the (terrestrial ecosystems) were more subject to greater risk of collapse because there were fewer links" in the food web, said Jessica Whiteside, assistant professor of geological sciences at Brown and co-author on the paper.

The boom-and-bust cycles that marked land-based ecosystems' erratic rebound were like "mini-extinction events and recoveries," said Randall Irmis, a co-author on the paper, who is a curator of paleontology at the Natural History Museum of Utah and an assistant professor of geology and geophysics at Utah.

The hypothesis, in essence, places ecosystems' recovery post-Permian squarely on the repopulation and diversification of species, rather than on an outside event, such as a smoothing out of climate. The analysis mirrors the conclusions reached by Whiteside in a paper published last year in Geology, in which she and a colleague argued that it took up to 10 million years after the end-Permian mass extinction for enough species to repopulate the ocean — restoring the food web — for the marine ecosystem to stabilize.

"It really is the same pattern" with land-based ecosystems as marine environments, Whiteside said. The same seems to hold true for plants, she added.

Some studies have argued that continued volcanism following the end-Permian extinction kept ecosystems' recovery at bay, but Whiteside and Irmis say there's no physical evidence of such activity.

The researchers examined nearly 8,600 specimens, from near the end of the Permian to the middle Triassic, roughly 260 million to 242 million years ago. The fossils came from sites in the southern Ural Mountains of Russia and from the Karoo Basin in South Africa. The specimen count and analysis indicated that approximately 78 percent of land-based vertebrate genera perished in the end-Permian mass extinction. Out of the rubble emerged just a few species, the disaster taxa. One of these was Lystrosaurus, a dicynodont synapsid (related to mammals) about the size of a German shepherd. This creature barely registered during the Permian but dominated the ecosystem following the end-Permian extinction, the fossil record showed. Why Lystrosaurus survived the cataclysm when most others did not is a mystery, perhaps a combination of luck and not being picky about what it ate or where it lived. Similarly, a reptilian taxon, procolophonids, were mostly absent leading to the end-Permian extinction, yet exploded onto the scene afterward.

"Comparison with previous food-web modeling studies suggests this low diversity and prevalence of just a few taxa meant that links in the food web were few, causing instability in the ecosystem and making it susceptible to boom-bust cycles and further extinction," Whiteside said.

The ecosystems that emerged from the extinction had such low animal diversity that it was especially vulnerable to crashes spawned by environmental and other changes, the authors write. Only after species richness and evenness had been re-established, restoring enough population numbers and redundancy to the food web, did the terrestrial ecosystem fully recover. At that point, the carbon cycle, a broad indicator of life and death as well as the effect of outside influences, stabilized, the researchers note, using data from previous studies of carbon isotopes spanning the Permian and Triassic periods.

"These results are consistent with the idea that the fluctuating carbon cycle reflects the unstable ecosystems in the aftermath of the extinction event," Whiteside said.

Friday, August 19, 2011

Researchers Complete First Major Survey of Amphibian Fungus in Asia

Rana similis, a frog species found in the Philippines.
The survey conducted by Vance Vredenburg and
colleagues found that this species has one of the
highest infection levels of the chytrid fungus in Asia
 and is potentially threatened by the disease. Photo
Credit: R. Brown, University of Kansas.

An international team of researchers has completed the first major survey in Asia of a deadly fungus that has wiped out more than 200 species of amphibians worldwide. The massive survey could help scientists zero in on why the fungus has been unusually devastating in many parts of the globe -- and why Asian amphibians have so far been spared the same dramatic declines.

The disease chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis or Bd, is the culprit behind amphibian extinctions in Central, South and North America, Australia and Europe. The new Asian survey of the fungus, which was published Aug. 16 in the journal PLoS One, shows that Bd is prevalent at very low levels in the region.

Asia is home to a highly diverse set of amphibian species, and potentially could be vulnerable to Bd. But Vance Vredenburg, assistant professor of biology, said very little is known about the fungus and its impact on the health of amphibians in Asia.

"That's why we're excited about this first really big survey," said Vredenburg, who led the research team. "If you look at chytrid worldwide, Asia's been the black hole in our data."

From 2001 to 2009, Vredenburg and his colleagues surveyed more than 3,000 amphibians -- mostly frogs -- from 15 Asian countries, swabbing the toe webbing, thigh and abdomen of the animals to pick up any signs of Bd, which infects the skin of amphibians.

They found that the prevalence of Bd was very low throughout the region, appearing in only 2.35 percent of the frogs. The Philippines, Kyrgyzstan, Laos, Indonesia, Malaysia and South Korea were the only countries with any Bd infection.

The survey suggests that Bd is either emerging in Asia, or may have been in Asia at low levels for a long time or that some other factor is preventing Bd "from fully invading Asian amphibians," the researchers write.

Each site in the study was only surveyed once, Vredenburg explained, so it's difficult to determine whether Bd infections in the countries are newly expanding. It will be critical, he said, "to see how Bd prevalence is changing through time, because this is key to understanding the ultimate outcome of the disease."

If Bd has been in Asia for a long time, researchers would like to know why amphibians there have managed to co-exist with a fungus that has proved so destructive elsewhere. It is possible, for instance, that Asian amphibians might bear some sort of bacterial protection against Bd in their skins.

Other scientists are analyzing the genes of the Bd fungus collected globally, Vredenburg said, "to find out whether strains from different parts of the world also differ in their virulence."

Vredenburg said the possibility of another wave of extinctions highlights the need to follow the Asian survey with further research to answer all of these questions.

And if Asia is on the brink of a chytrid epidemic, Vredenburg and colleagues think it might start in the Philippines. "The prevalence and intensity of Bd infection is much higher here than anywhere else in Asia," he said. "Bd in the Philippines today looks similar to Bd in early outbreaks in California and South and Central America."

"This study is the first important step to understanding Bd in Asia," Vredenburg said. "It provides a solid foundation that future studies can build upon."

Link to Original Article: Swei A,  et al. (2011) Is Chytridiomycosis an Emerging Infectious Disease in Asia? PLoS ONE 6(8): e23179. doi:10.1371/journal.pone.0023179

Sunday, May 29, 2011

Modern EU Agriculture Jeopardises Biodiversity in New Member States

A new study from Romania highlights the importance of traditional agriculture in protecting amphibians.

Traditional agricultural practices can make a major contribution to preserving biodiversity in the EU’s new member states in Central and Eastern Europe. By contrast, the construction of roads and the intensification of agriculture currently encouraged by EU farming subsidies pose a threat to amphibians. The rich natural environment still extant in many accession countries is under threat, according to scientists writing in the journal Biological Conservation.

The researchers from Romania, Germany and the Netherlands investigated amphibians for their study in the Romanian province of Transylvania. They spent nine years studying the populations of various species of newts, frogs and toads in 54 ponds and related their performance to nearby land use.

All in all, the scientists found 10 amphibian species in the surveyed ponds, including EU-wide protected species like the Great Crested Newt and the Yellow Bellied Toad. Statistical evaluation revealed that roads had the biggest impact on their populations. Other factors like the size of ponds, building development, farmland, pasture, woodland and marshlands proved to be far less important. "Roads have a direct negative effect on many species of amphibians, which can get run over by cars. But roads also have an indirect impact, for example by the destruction and isolation of the critical habitats for amphibians such as breeding, summering and overwintering habitats" explained Dr Tibor Hartel from Babeş-Bolyai University, Cluj-Napoca (Romania).

The study area was the "Saxon area" of Southern Transylvania along the Târnava Mare basin in Romania. The agriculture is still largely traditional in this region, sometimes with little changes through the centuries. The landscape is dominated by pasture and deciduous forest, while the arable lands are small sized and scattered across the native grassland vegetation. Mankind’s negative impact on biological diversity is statistically still far lower in Eastern Europe than in the West - but this traditional cultural landscape and hence its unique biodiversity could soon disappear if agriculture were to be intensified. "We believe that the comparatively extensive agriculture in the study region with little machinery and hardly any chemicals provides conditions which are still suitable for many amphibian species," explains Dr Oliver Schweiger from UFZ.
The findings could have important consequences for protective measures for amphibians in regions of Central and Eastern Europe, where farming has remained largely traditional. Preserving traditional, extensive land management could be the key factor in protecting these species. However, that could be a tough challenge, for many regions, joining the EU will lead to more intensive land use and infrastructure expansion. And that in turn will result in the fragmentation of the landscape and the general deterioration of the remaining habitats. Researchers are now calling for a balance to be struck between the legitimate desire for improved infrastructure and higher agricultural yields on the one hand and the beneficial effects of extensive land use on the other. In their view, this challenge should be regarded as an opportunity for Eastern Europe not to repeat the mistakes made in the West.

Photos: The common toad, Bufo bufo. And an agricultural pond Photo credits: Tibor Hartel/Babes-Bolyai-Universität Cluj-Napoca.

Friday, May 6, 2011

The Spread of an Amphibian Epidemic, Bd in Mesoamerica

Male (top) and female (bottom)
Golden Toads, Incilius periglenes
(Savage, 1967). Monteverde, Costa
Rica. Described by science in 1967
it is likely now extinct, the victim of
 Bd. This was a lower montane
rainforest species. JCM
Evidence suggests that we are seeing the start of the 6th mass extinction event in Earth's history, and some of the evidence comes from amphibians, 40% of which are considered endangered. Hypotheses have implicated habitat destruction, overexploitation, pollution, and climate change in the loss of amphibians, but the infectious fungal disease, chytridiomycosis, has been the main suspect in the disappearance of many different species in many different families in geographically distant locations. The chytridiomycete fungus Batrachochytrium dendrobatidis (Bd) has a flagellated infective life stage called the zoospore that penetrates the skin of amphibians causing hyperkeratosis, this results in a loss of skin function, osmoregulatory failure, and death. First reported in 1999, Bd has been shown to be closely associated with the collapse of amphibian populations in Australia, Panama, California, and Peru and has been linked to amphibian declines that occurred decades ago. Bd is unusual because multiple host species in at least one locality have been extripated before density-dependent factors could slow the spread of disease. Now, Tina Cheng and colleagues (2011) present evidience on how Bd has spread using museum specimens from vanished populations. Using two well-studied cases of amphibian decline in Mesoamerica: the decline and disappearance of anurans from Costa Rica’s Monteverde Reserve in the late 1980s, and the decline and disappearance of plethodontid salamanders from the mountains of southern Mexico and western Guatemala in the 1970s and 1980s, the authors test retroactively whether Bd emergence was linked to earlier declines and extinctions. They use a noninvasive PCR sampling technique that detects Bd in formalin-preserved museum specimens and found Bd using the PCR technique in 83–90% (n = 38) of samples that were identified as positive by histology. They examined specimens collected before, during, and after major amphibian decline events at established study sites in southern Mexico, Guatemala, and Costa Rica and found a pattern of Bd emergence coincident with decline at these localities. The absence of Bd over multiple years at all localities followed by the concurrent emergence of Bd in various species at each locality during a period of population decline. The geographical and chronological emergence of Bd at these localities suggests a southward spread from southern Mexico in the early 1970s to western Guatemala (1980s/1990s), and to Monteverde, Costa Rica (1987); thus the authors found evidence of a historical “Bd epidemic wave” that began in Mexico and subsequently spread to Central America. The full article is available on-line, follow the link below.

Citation

Tuesday, April 26, 2011

Amphibian Declines, Multiple Causes

Oregon State University
The following is a press release from Oregon State University.

CORVALLIS, Ore. – Amphibian declines around the world have forced many species to the brink of extinction, are much more complex than realized and have multiple causes that are still not fully understood, researchers conclude in a new report.

The search for a single causative factor is often missing the larger picture, they said, and approaches to address the crisis may fail if they don’t consider the totality of causes – or could even make things worse.

No one issue can explain all of the population declines that are occurring at an unprecedented rate, and much faster in amphibians than most other animals, the scientists conclude in a study just published in the Annals of the New York Academy of Sciences.

The amphibian declines are linked to natural forces such as competition, predation, reproduction and disease, as well as human-induced stresses such as habitat destruction, environmental contamination, invasive species and climate change, researchers said.

“An enormous rate of change has occurred in the last 100 years, and amphibians are not evolving fast enough to keep up with it,” said Andrew Blaustein, a professor of zoology at Oregon State University and an international leader in the study of amphibian declines.

“We’re now realizing that it’s not just one thing, it’s a whole range of things,” Blaustein said.

“With a permeable skin and exposure to both aquatic and terrestrial problems, amphibians face a double whammy,” he said. “Because of this, mammals, fish and birds have not experienced population impacts as severely as amphibians – at least, not yet.”

The totality of these changes leads these researchers to believe that the Earth is now in a major extinction episode similar to five other mass extinction events in the planet’s history. And amphibians are leading the field – one estimate indicates they are disappearing at more than 200 times that of the average extinction rate.

Efforts to understand these events, especially in the study of amphibians, have often focused on one cause or another, such as fungal diseases, invasive species, an increase in ultraviolet radiation due to ozone depletion, pollution, global warming, and others. All of these and more play a role in the amphibian declines, but the scope of the crisis can only be understood from the perspective of many causes, often overlapping. And efforts that address only one cause risk failure or even compounding the problems, the researchers said.

“Given that many stressors are acting simultaneously on amphibians, we suggest that single-factor explanations for amphibian population declines are likely the exception rather than the rule,” the researchers wrote in their report. “Studies focused on single causes may miss complex interrelationships involving multiple factors and indirect effects.”

One example is the fungus B. dendrobatidis, which has been implicated in the collapse of many frog populations around the world. However, in some populations the fungus causes no problems for years until a lethal threshold is reached, studies have shown.

And while this fungus disrupts electrolyte balance, other pathogens can have different effects such as a parasitic trematode that can cause severe limb malformations, and a nematode that can cause kidney damage. The combination and severity of these pathogens together in a single host, rather than any one individually, are all playing a role in dwindling frog populations.

Past studies at OSU have found a synergistic impact from ultraviolet radiation, which by itself can harm amphibians, and a pathogenic water mold that infects amphibian embryos. And they linked the whole process to water depths at egg-laying sites, which in turn are affected by winter precipitation in the Oregon Cascade Range that is related to climate change.

The problems facing amphibians are a particular concern, scientists say, because they have been one of Earth’s great survivors – evolving about 400 million years ago before the dinosaurs, persisting through ice ages, asteroid impacts, and myriad other ecological and climatic changes.

Their rapid disappearance now suggests that the variety and rate of change exceeds anything they have faced before, the researchers said.

“Modern selection pressures, especially those associated with human activity, may be too severe and may have arisen too rapidly for amphibians to evolve adaptations to overcome them,” the researchers concluded.