UPDATE: Earth May Be in Early Days of 6th Mass Extinction

Earth May Be in Early Days of 6th Mass Extinction - Yahoo News Philippines: "the looming sixth mass extinction is linked to human activity, Rodolfo Dirzo, a professor of biology at Stanford University in California, said in a statement. Dirzo is the lead author of the new review of past research on the topic, which suggests Earth is in the early days of this sixth mass extinction.
A past study, which involved data from the fossil record and modern-day conservation biology, suggested Earth could enter such a mass extinction within the next 300 to 2,000 years. That study was detailed in the March 2, 2011, issue of the journal Nature.
Up to one-third of all vertebrates are threatened or endangered, the researchers said. Large animals — such as elephants, rhinoceroses and polar bears — have the highest rates of decline, which is a trend shared by other mass extinctions. These large animals are at particular risk because they tend to have few offspring and low population growth rates. Hunters and poachers, however, find their fur, meat, tusks or horns attractive targets. [7 Iconic Animals Humans Are Driving to Extinction]
Losing a species of large animal can have unexpected effects on the ecosystem and nearby human developments, a process known as defaunation. In one study, researchers isolated patches of land from animals, including zebra, giraffes and elephants. Without the animals, the grass and shrubs grew tall, and the soil became looser. Rodents quickly took over and doubled in numbers, eating the seeds from the plants and living in the patchy soil that was relatively predator-free.
Rodents can carry diseases and parasites that infect people, the researchers said.
"Where human density is high, you get high rates of defaunation, high incidence of rodents and thus high levels of pathogens, which increases the risks of disease transmission," Dirzo said. "Who would have thought that just defaunation would have all these dramatic consequences? But it can be a vicious circle.""



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