Thursday, October 13, 2011

IUCN "Red List" documents continuing extinction crisis

IUCN "Red List" documents continuing extinction crisis

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Lately my work on another project has meant spending time with one of the most depressing documents people have ever produced. It’s the “Red List of Threatened Species” published by the International Union for the Conservation of Nature, which is an umbrella organization that coordinates scientific efforts to catalogue and preserve biodiversity worldwide.

Updates to the Red List are published every four years, and the version I’ve been looking at comes from 2008. Its authors point out that it contains glimmers of hope, but then they characterize the news it holds this way: “The overwhelming message is that the world is losing species and that the rate of loss is accelerating in many taxonomic groups.”

Scientists know much more about the state of vertebrates—especially mammals, birds, and amphibians—than they do about other forms of animal life. Every one of the 5,488 species of mammals that have been described, for example, has been evaluated for purposes of the Red List. Of them, 76 species have become extinct since the year 1500, and two, Pere David’s deer, which is native to Asia, and the scimitar oryx from Africa survive only in managed facilities. Another 29 of the mammal species listed as critically endangered are also tagged as “possibly extinct”; they are very likely gone, but the sort of exhaustive surveys required to confirm that fact have not been conducted. Overall, approximately 22% of mammal species worldwide are known to be threatened or extinct.

The Red List categorizes a smaller proportion of the world’s 9,990 bird species—14%—as threatened or extinct. But the raw number of bird species lost over the past five centuries is at least 134, and four more species persist only in zoos. Another 15 species of birds are considered possibly extinct. The fact that 86% of bird species are categorized as “not threatened” constitutes really good news in the context of the Red List.

Among the well-studied vertebrates, amphibians are faring especially poorly. Of the more than 6,000 known species of frogs, toads, salamanders and the like, 38 have become extinct worldwide since 1500, 11 of those in just the last three decades. [USFWS photo: The Monteverde golden toad is one of 11 species of amphibians to become extinct since 1980.] Another one, the Wyoming toad, survives only in a recovery program, and another 120 species are considered possibly extinct. Overall, about a third of the world’s amphibian species are known to be threatened or extinct.

Of course, this information about familiar, terrestrial creatures is just a small part of what the Red List covers. It also documents disturbing facts about marine life, from plummeting fish stocks to large-scale declines among reef-building corals, and more.

I should emphasize that even taken as a whole, the Red List does not provide a comprehensive picture of life on earth. Scientists have described fewer than 2 million of the 8-9 million species of organisms thought to exist, most of which are insects, and only a fraction of those described species have been evaluated for purposes of the Red List.

The threats that put species at risk vary from one to another, but most of them result from human activity. People convert wild land to agriculture. We strip it to get at minerals. We build roads and cities. We cut down trees and kill animals at unsustainable rates, and we wreck ecosystems by introducing invasive species.

None of this is to say people are not capable of altering their behavior to prevent the extinction of other species. But on the whole, it’s difficult to spend time with the Red List and come away with a lot of hope.