12.3: Rates of Extinction

If extinction and speciation are natural processes, an obvious question follows: “Why should we care about the loss of biodiversity?” The answer concerns not individual species extinctions as much as the increasing rate of these extinctions (Figure 12.3.1 and 12.3.2). While a species can be wiped off Earth over a relatively short period of time, speciation typically occurs slowly as the genetic makeup of a population shifts over thousands of years. Unfortunately, we are currently losing species 1,000 times faster than natural background extinction rates (for mammals estimated to be 1.8 extinctions per 10,000 species per 100 years, Barnosky et al., 2011), and future rates may be 10,000 times higher that background rates (de Vos et al., 2015). Because over 99% of current species extinctions have been linked to human activity rather than natural processes (Pimm et al., 2014), observations on past extinctions and subsequent speciation may not apply to the present. Moreover, unlike before, humans now share the planet with the species we are wiping out. These losses mean that we are also losing the benefits we gain from nature at unprecedented rates.

Figure 12.3.1: Global rates of extinction and risk of extinction has increased dramatically. A. Percentage of species threatened with extinction according to assessments by the IUCN Red List. B. Extictions for vertebrate groups since 1500. C. Red List Index for different groups assessed by the IUCN. A value of 1 is equivalent to all species classified as least concern and a value of 0 is equal to all species in the group extinct. (IPBES Global Assessment report 2019, data from IUCN Red List )

Figure 12.3.2 Percentage of Sub-Saharan Africa invertebrates, plants, reptiles, and mammals that have gone Extinct, Extinct in the Wild, and likely Extinct since the year 1500. Dashed line represents the natural rate of extinctions expected without human influences. After Ceballos et al., 2015, CC BY 4.0.