The order Primates is one of the most diverse groups of mammals on the planet, with over 528 species in 81 different genera currently recognized (IUCN SSC Primate Specialist Group 2022). In the last few decades new genera, species, and subspecies of primates have been recognized—sometimes as a result of new discoveries and new data but also because of revisions to taxonomic classification systems based on different species concepts (Groves 2014; Lynch Alfaro et al. 2012; Rylands and Mittermeier 2014).
Wild primates occur in 90 countries around the world, but two-thirds of all species are found in only four countries: Brazil, Madagascar, Democratic Republic of Congo, and Indonesia (Estrada et al. 2017; Estrada et al. 2018). An estimated 66% of primate species are threatened with extinction (Fernández et al. 2022; Figure B.2). Yet despite this discouraging statistic, there are a growing number of populations recovering as a result of research and conservation efforts. For example, the population of mountain gorillas (Figure B.3) initially studied by Dian Fossey in Rwanda in 1967 has grown from 250 gorillas in 1981 to 339 in 2008. The increase is a result of ongoing research and conservation efforts that include highly controlled ecotourism (Robbins et al. 2011). Similarly, one population of northern muriqui monkeys (Figure B.4)—which inhabits a small, privately owned forest fragment in southeastern Brazil’s Atlantic Forest—increased from about 50 individuals to nearly 350 individuals as a result of increased habitat protection over the course of the Muriqui Project of Caratinga, a long-term field study initiated nearly 40 years ago by one of the authors of this appendix (Strier and Mendes 2012). Although the population has declined by about ⅓ in the past five years, it is still 4–5 times larger than it was 40 years ago (Strier 2021a).
In conservation, it is crucial to have a global standard to assess and recognize the conservation status of species. The International Union for the Conservation of Nature (IUCN) formed the Red List for Threatened Species in 1994 to determine species extinction risks (IUCN 2022). Scientists submit assessments of species to the IUCN, which are subsequently categorized based on the size and distribution of species’ numbers and available habitat. The categories range from “data deficient,” when not enough is known, to “least concern,” “near threatened,” “vulnerable,” “endangered,” “critically endangered,” “extinct in the wild,” and “extinct.” Threatened species are classified as “vulnerable,” “endangered,” or “critically endangered,” with the most critically endangered species being those whose numbers are fewer than 250 mature individuals and continuing to decline or whose habitats are severely fragmented (Figure B.5; IUCN 2022).
Critically Endangered (CR): Facing an extremely high risk of extinction in the wild due to any of the following:
Endangered (EN): Facing a very high risk of extinction in the wild due to any of the following:
Vulnerable (VU): Facing a high risk of extinction in the wild due to any of the following:
The IUCN has a committee specifically dedicated to primates, the IUCN Species Survival Commission (SSC) Primate Specialist Group. This group collaborates with the International Primatological Society (IPS), Conservation International (CI), and the Bristol Zoological Society (BZS) every two years to publish “Primates in Peril: The World’s 25 Most Endangered Primates.” These lists are created at IPS open meetings and are intended to focus attention on all endangered primates by highlighting the plights of some of the most critically endangered (Mittermeier et al. 2022).
It is important to consider extinction risk in making conservation decisions, thus the IUCN Red list and the “Primates in Peril” reports are factors in deciding how to allocate resources and funding. Some primate species are found only in biodiversity hot spots or in areas that contain high levels of species diversity and include primates that are endemic to the area and genetically unique (Sechrest et al. 2002). Hot spots are often considered conservation priorities because protecting these areas can result in the protection of large numbers of species. In addition, some conservation organizations focus on highly charismatic primate species (e.g., primates that are large, closely related to humans, or well-known from zoos) to garner attention and resources for conservation (Figure B.6). However, dramatic declines of charismatic species indicate that charisma is not enough (Estrada et al. 2017). In making conservation decisions, primatologists may also consider the importance of genetically unique primates—such as the aye-aye (Daubentonia madagascariensis), the last remaining species within its genus—in order to preserve evolutionary history (Strier 2011a).