Extinction Alarmists or True Species Loss?

Species extinction rates often overestimate actual rates of extinction. Why is that and what causes changes in these rates in the first place? 

Species extinctions, whether it be the extinction of plants or animals, are measured by extinction rates. An extinction rate represents the number of species that go extinct over a period of time. It is often easier to break down a seemingly abstract rate, like a species extinction rate, down into a digestible number. Statistics like “[e]very day, up to 150 species are lost” make it easy to visualize the loss of organisms (Djoghlaf et al. 1). However, it has been found that generalizations like this can be very inaccurate and don’t accurately represent the actual extinction rate of plants or animals.

How are extinction rates usually measured?

Extinction rates are often measured through some sort of model. By using a set of circumstances and data, an understanding of the number of species going extinct at a given time can be built. 

One of such models is a species-area model. This looks at the size of a habitat and the number of species present in the habitat. Another way extinction rates are modeled is through using past extinctions to inform predictions made about extinction patterns today. By using prior occurrences to build the model, it can be seen what trajectory the currently endangered populations might follow. The rankings of the species on various red lists can inform the predictions about the rate of extinction. A red list summarizes currently threatened and endangered species. There are a few different analyses methods used within the practice of using the red lists, but they all are based on using the records of threatened and endangered species from red lists. One prominent red list is the ICUN Red List. 

Co-extinction is both the cause for some species’ extinctions, as well as a way to evaluate the rate of extinction. As species go extinct, the species that are dependent upon them will also go extinct as a result of their dependence. By understanding which species are dependent on which, the extinction rate can be constructed. Similarly, climate change models can help to build an understanding for the ways in which species will be impacted by climatic impacts like rising temperatures, while climate change itself is also a major cause for extinction rates themselves. 

The Ivory-billed Woodpecker is an example of a species that recently went extinct in the US.

What factors could cause extinction rates to be inaccurate? 

We have many different estimates of the number of species of organisms present on earth. Furthermore, new species are being discovered every day at the same time as other species are going extinct, which also makes it difficult to be precise. Without very accurate documentation on the number of species going extinct, nor with documentation of the undiscovered species, it's nearly impossible to give one accurate estimated extinction rate. 

It is important to keep in mind these methods are models, and such models are only as accurate as the circumstances and data that are informing them are precise. Furthermore, the conditions that one extinction event occurs under will likely be different from other extinction events, which also makes calculating extinction rates based off of previous events difficult. 

Furthermore, in recent years particularly effective conservation efforts have been able to reduce extinction rates, which could also explain a discrepancy between the calculated rates and the actual number of species going extinct. 

Summing extinction into one number is very tedious; however, we often have a good idea of what causes specific cases of extinction, which can help to guide conservation efforts. While the numbers may not be exact we can use documentation like red lists to understand what species are going extinct. 

By Anna Cerosaletti

Sources: 

Djoghlaf, Ahmed, et al. Message from Mr. Ahmed Djoghlaf, Executive Secretary, on the Occasion of The International Day for Biological Diversity. 22 May 2007.

Nakamura, Kate. “22 Animals That Went Extinct in the US in 2021 — and How to Take Action for Biodiversity.” Global Citizen, 14 December 2021, https://www.globalcitizen.org/en/content/animal-extinct-biodiversity-2021/. Accessed 6 November 2022.

National Aeronautic Space Administration. “Scientific Consensus | Facts – Climate Change: Vital Signs of the Planet.” Global Climate Change, https://climate.nasa.gov/scientific-consensus/. Accessed 6 November 2022.

Pearce, Fred. “Global Extinction Rates: Why Do Estimates Vary So Wildly?” Yale E360, 17 August 2015, https://e360.yale.edu/features/global_extinction_rates_why_do_estimates_vary_so_wildly. Accessed 6 November 2022.

Stork, Nigel E. “Re-assessing current extinction rates.” Biodiversity Conserv, vol. 19, 2010, pp. 357-371.