Study finds hundreds of thousands of tropical species at risk of extinction due to deforestation

Photo by Rhett Butler.

Photo by Rhett Butler.

MONGABAY

May 8th, 2017

By: Mike Gaworecki

A 2015 study found that humans activities are driving species loss at a rate 100 times faster than historical baseline levels — which the researchers behind the study characterized as a conservative estimate. This finding fueled speculation that we’re currently witnessing a sixth global mass extinction event.

New research published in the Proceedings of the National Academy of Sciences (PNAS) provides further evidence that, even if we haven’t already entered a sixth era of mass species loss on a global scale, it may yet be imminent.

John Alroy, a professor of biological sciences at Australia’s Macquarie University, examined local-scale ecological data in order to forecast potential global extinction rates and found that hundreds of thousands of species are at risk if humans disturb all pristine forests remaining in the tropics. “Disturbance is no small matter, because roughly two-thirds to three-quarters of all the world’s species are found in tropical forests even though tropical forests only cover about 10 percent of the entire Earth’s continental area,” Alroy said in a statement.

Scientists have long believed that the rate at which we are destroying tropical forests, and the habitat those forests represent, could drive a global mass extinction event, but the extent of the potential losses has never been fully understood.

Mass extinction will occur primarily in tropical forests because Earth’s terrestrial biodiversity is so heavily concentrated in those ecosystems, Alroy notes in the study. In order to examine just how severe the impacts might be, he applied a highly accurate method of estimating species richness to data from 875 ecological samples of trees and 10 other groups of organisms “of keen ecological interest,” including bats, insects (ants, butterflies, mosquitoes, and scarabs), large and small mammals, and other vertebrates (birds, frogs, and lizards). The samples were collected in a variety of habitat types in tropical zones that were originally forested, from primary and fragmented forests to plantations and pasturelands.

“About 41% of the tree and animal species in this dataset are absent from disturbed habitats, even though most samples do still represent forests of some kind,” Alroy writes in the study.

Alroy projects that, if Earth’s remaining tropical forests are completely disturbed, more than 18 percent of species will be lost in every group studied except large mammals and mosquitoes. Seven of the groups he examined will lose greater than 28 percent of species. Trees, for instance, stand to lose as much as 30 percent of species, while ants could lose as much as 65 percent.

“The overall implication of this research is that any substantial loss of primary forests will result in numerous extinctions across many groups,” Alroy said. He added that there is good reason to regard his estimates as conservative, as well, and that the full impacts of human activities on species survival could be more severe than he has predicted: “Even if we preserve forests of some kind in many places, unless we protect them from ever being logged, those forests may end up being empty.”

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