About half of the roughly 300 primate species worldwide are threatened, and knowing which species are likely to be harmed by which threats is key to protecting them. In the most comprehensive such analysis to date, researchers assessed primates’ vulnerabilities to forestry, agriculture, and hunting and then linked these vulnerabilities to underlying biological traits.
“This information should help us gain a deeper understanding of the processes that underpin this global pattern and therefore ultimately prevent such global extinctions from taking place,” say Nick Isaac and Guy Cowlishaw of the Zoological Society of London in the June 7 issue of Proceedings of the Royal Society: Biological Sciences.
Using existing data, Isaac and Cowlishaw compared the abundance of primate species in threatened and non-threatened areas around the world. Habitat loss and hunting are the biggest threats to primates, and each threatened area studied had experienced either forestry (selective logging), agriculture (shifting cultivation), or hunting. The researchers determined the vulnerability of 66 primate species to forestry, 44 to agriculture, and 54 to hunting. They also assessed whether vulnerability to each threat were linked to any of six biological traits: ecological flexibility, habitat, diet, body size, home range, and sociability.
Isaac and Cowlishaw found that the primates’ vulnerabilities varied tremendously. Some species are vulnerable to all three threats: the white-bellied spider monkey (Ateles belzebuth belzebuth), for example, is locally extinct in all of the threatened areas studied. In contrast other species are vulnerable to only one of the threats studied: the collared titi monkey (Callicebus torquatus), for example, is extremely vulnerable to agriculture but is tolerant of forestry and hunting. Of all the species that were studied in more than one type of threatened area, nearly half (24 of 52) are susceptible to one threat but tolerant of another.
The researchers also found that primate species vulnerable to one of the three threats are not more likely to be vulnerable to either of the others. Notably, species vulnerable to forestry are not necessarily also vulnerable to agriculture, even though both threats are types of habitat disturbance. This is presumably because different biological traits underlie the species’ vulnerabilities to the threats studied. Primate species living in a relatively narrow temperature range tend to be more vulnerable to forestry, which makes sense because logged forests get hotter during the day and colder at night than do un-logged forests. In contrast, primate species that live in the canopy and eat low-fruit diets tend to be more vulnerable to agriculture; this makes sense because shifting agriculture typically replaces all trees except those that bear fruit. And, not surprisingly, primate species that are vulnerable to hunting tend to be larger, which probably makes them more attractive to hunters.
“Our analyses demonstrate that a species’ vulnerability to local extinction is highly variable, depending on the anthropogenic activity that threatens it,” say Isaac and Cowlishaw. “This marked threat specificity provides a cautionary lesson about the dangers of making broad generalizations about species’ vulnerabilities to extinction.”
Isaac, N.J.B. and G. Cowlishaw. 2004. How species respond to multiple extinction threats. Proceedings of the Royal Society: Biological Sciences 271(1544):1135-1141.
Western lowland gorilla (Gorilla g. gorilla graueri) Photo by Troy Inman