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Study: Extreme losses in a few animal populations explain global vertebrate declines

Nov. 18 (UPI) — The planet’s vertebrates aren’t doing as poorly as previous surveys have suggested.

According to a new study, published Wednesday in the journal Nature, declines in global vertebrate numbers are largely driven by extreme losses among a handful of animal populations.

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When biologists separated out the populations responsible for the most precipitous declines, they revealed a more positive portrait of global biodiversity.

Using historical wildlife monitoring data, researchers previously estimated that vertebrate populations have declined by roughly 50 percent over the last 50 years.

“However, given previous mathematical methods used to model vertebrate populations, this estimate could arise from two very different scenarios: widespread systematic declines, or a few extreme declines,” senior study author Brian Leung, an ecologist at McGill University in Canada, said in a news release.

Because populations are composed of individuals of the same species living in a specific location, severe population declines precede the loss of species and biodiversity declines.

For the study, researchers surveyed data for 14,000 vertebrate populations collected in the Living Planet Database. Scientists determined roughly 1 percent of the vertebrate populations have experienced extreme declines over the last half-century, including reptiles in tropical areas of the Americas and birds in the Indo-Pacific.

“Extreme declines occur disproportionately in larger animals,” researchers wrote in the paper.

When rapidly declining populations are taken out of the dataset, researchers found the absence of a general trend, positive or negative, among the remaining vertebrate populations.

“We were surprised by how strong the effect of these extreme populations was in driving the previous estimate of average global decline,” said co-author Anna Hargreaves, a professor of biology at McGill.

Though the research paints a more positive picture of vertebrate biodiversity than previous studies, the data, when broken down further, suggests many vertebrate populations are struggling.

“Our results identify regions that need urgent action to ameliorate widespread biodiversity declines, but also reason to hope that our actions can make a difference,” Hargreaves said.

Researchers identified steady population declines among vertebrates living throughout the Indo-Pacific, especially reptile and amphibian groups.

“Some populations really are in trouble and regions such as the Indo-Pacific are showing widespread systematic declines. However, the image of a global ‘biodiversity desert’ is not supported by the evidence.” says Leung. “This is good, as it would be very discouraging if all of our conservation efforts over the last five decades had little effect.”

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