Climate change vs. human activity

Human activity has had at least as much effect as climate change on the survival of animals on the Bahamian island of Abaco, a new study suggests. Researchers looked at 10,000-year-old fossils found in an underwater cave on Abaco.

They compared them with fossils from the island that date to 1,000 to 3,000 years ago, along with data from current vertebrate populations.

The scientists found that during the last ice age, about 10,000 years ago, some 17 bird species went extinct on Abaco because of a warming, wetter climate and rising sea levels.
“All of these birds were open country birds that preferred grassy, dry, cool climates,” said David Steadman, curator of ornithology at the Florida Museum of Natural History and one of the study’s authors.

At that time, there were no humans on the island. About 1,000 years ago, the first humans arrived and about 22 species became extinct. The latter species were far more diverse, compared with those that became extinct at the end of the last ice age, and included a tortoise, a crocodile, bats, and little and big birds.

The study offers a sobering message about the extent of human impact, David said. “The species that were lost in the last 1,000 years were resilient to natural changes,” he said. “They could handle the climate getting warmer and wetter, but they couldn’t handle it when humans showed up.” The findings appear in Proceedings of the National Academy of Sciences.

Causes for dinosaurs’ extinction
For decades, researchers have debated whether a major asteroid strike or enormous volcanic eruptions led to the demise of dinosaurs almost 66 million years ago. According to a new study, the answer might be somewhere in between: The asteroid impact accelerated the eruptions of volcanoes, and together, these catastrophes led to the mass extinction.

“The community is divided between whether one was the more important or more relevant cause,” said Paul Renne, a geochronologist at the University of California, Berkeley, and one of the study’s authors. “What we are saying now is that it may not be realistic to view them as competing effects.”

He and his colleagues reported their findings in the journal Science. For their research, they collected about 700 rock samples from the Deccan Traps, a geological feature in India caused by vast floods of lava. The basalt formation covers more than 2,00,000 square miles and is more than a mile thick in some places. “What we were really trying to do was sample from the bottom of the traps through the top,” Paul said.

They shipped these samples back to the University of California, and with a process called argon-argon dating, they determined that the eruptions that formed the Deccan Traps started doubling in output within 50,000 years of the asteroid impact that preceded the dinosaur extinction.

“What we think is that the impact may have somehow accelerated those eruptions,” said Mark Richards, a geophysicist at the University in Berkeley and an author of the study. Exactly how is unclear, although the researchers have some theories.

“There may have been a major change in permeability of the crust, causing
magma to flow much more freely after the asteroid,” Paul said.

Frog species are on a decline
Since the 1970s, frog populations have been in decline. A new study in Proceedings of the National Academy of Sciences reports that at least 3.1 per cent of frog species have gone extinct, and another 6.9 per cent may disappear within the next century.

John Alroy, a biologist at Macquarie University in Australia and the study’s
 author, computed extinction probabilities for species of frogs around the world by building a statistical model based on sighting frequency and last date of sighting.

The study found that frog species are at risk for a number of reasons — including epidemics caused by pathogens like the fungus B dendrobatidis, deforestation, invasive species, and climate change.