Mysterious math
Considering the estimate of 100 extinctions per one million species per year in Covey’s research, we conclude that 100,000 of the two million known species have become extinct in the past 500 years. However, the statistics of unknown animals are not included in this category.
According to a study published in PLOS Biology in 2011, there are approximately 7.7 million animal species. According to this figure, if we apply 100 extinctions per one million species over the past 500 years and subtract the 3859 species of animals that have become naturally extinct in this period with a background extinction rate of one extinction per one million species. The final estimate of the number of animal extinctions due to human activities reaches 381,150 species. However, such an estimate is approximate and should be viewed with skepticism.
John Alroy, an assistant professor in the School of Biological Sciences at Maccayer University in Australia who is assessing the quantity and diversity of extinctions, believes that it is almost impossible to calculate the speed of modern extinctions. He says:
We should be overly cautious about the accuracy of the data based on the available data. I feel like we don’t have a good handle on the current extinction rate.
To understand the overall extinction rate, researchers first need to know how many species there are. Not only is much of the world’s wildlife unknown to science, but often the highest densities of species are found in areas such as the tropics that are less studied. Worst of all, there are more insect species than all animal species combined. However, compared to larger animal groups such as mammals and birds, we know less about them.
Although difficult, Ellroy suggests that it is possible to estimate extinction rates by using museum data for specific groups of animals that are representative of larger groups and studying how many species have been lost over time. Regardless of the rate of extinction, it is clear that humans have exacerbated the process of extinction, and the number of extinctions is far greater than the 777 species listed on the IUCN Red List.
The wide range of E/MSY estimates presented in different studies so far have one thing in common: they are all much higher than the background extinction rate. This evidence is enough to say that humans are harming biodiversity on earth. Covey says:
Whether the extinction rate is 100, 20, or 200 E/MSY, it’s still very high and really bad.
