EXTINCTIONS

     
Extinctions have been a natural part of the planet’s evolutionary history. 99% of the four billion species that have evolved on Earth are now gone.1 Most species have gone extinct.

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But when people ask the question of how many species have gone extinct, they’re usually talking about the number of extinctions in recent history. Species that have gone extinct, mainly due to human pressures.

The IUCN Red các mục has estimated the number of extinctions over the last five centuries. Unfortunately we don’t know about everything about all of the world’s species over this period, so it’s likely that some will have gone extinct without us even knowing they existed in the first place. So this is likely lớn be an underestimate.

In the chart we see these estimates for different taxonomic groups. It estimates that 900 species have gone extinct since 1500. Our estimates for the better-studied taxonomic groups are likely to be more accurate. This includes 85 mammal; 159 bird; 35 amphibian; & 80 fish species.

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Species threatened with extinction today


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To understand the biodiversity problem we need to lớn know how many species are under pressure; where they are; and what the threats are. To vày this, the IUCN Red danh mục of Threatened Species evaluates species across the world for their cấp độ of extinction risk. It does this evaluation every year, & continues to lớn expand its coverage.

The IUCN has not evaluated all of the world’s known species; in fact, in many taxonomic groups it has assessed only a very small percentage. In 2021, it had assessed only 7% of described species. But, this very much varies by taxonomic group. In the chart we see the giới thiệu of described species in each group that has been assessed for their level of extinction risk. As we’d expect, animals such as birds, mammals, amphibians have seen a much larger mô tả of their species assessed – more than 80%. Only 1% of insects have. And less than 1% of the world’s fungi.

The lack of complete coverage of the world’s species highlights two important points we need lớn remember when interpreting the IUCN Red danh sách data:

Changes in the number of threatened species over time does not necessarily reflect increasing extinction risks. The IUCN Red list is a project that continues to expand. More và more species are been evaluated every year. In the year 2000, less than 20,000 species had been evaluated. By 2021, 140,000 had. As more species are evaluated, inevitably, more will be listed as being threatened with extinction. This means that tracking the data on the number of species at risk of extinction over time doesn’t necessarily reflect an acceleration of extinction threats; a lot is simply explained by an acceleration of the number of species being evaluated. This is why we vì not show trends for the number of threatened species over time.

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The number of threatened species is an underestimate. Since only 7% of described species have been evaluated (for some groups, this is much less) the estimated number of threatened species is likely lớn be much lower than the actual number. There is inevitably more threatened species within the 93% that have not been evaluated.

We should also define more clearly what threatened with extinction actually means. The IUCN Red danh sách categorize species based on their estimated probability of going extinct within a given period of time. These estimates take into tài khoản population size, the rate of change in population size, geographical distribution, and extent of environmental pressures on them. ‘Threatened’ species is the sum of the following three categories:

Critically endangered species have a probability of extinction higher than 1/2 in ten years or three generations;Endangered species have a greater than 20% probability in đôi mươi years or five generations;Vulnerable have a probability greater than 10% over a century.