Is the gorilla a threatened species? How should we judge?

Abstract

The question of whether the gorilla is a threatened species is part of the larger issue of how we judge the damage that we are doing to the world. Many criteria are being used. Here I apply to the gorilla Gorilla gorilla the newly suggested IUCN criteria for categorising the conservation status of all species, both to reassess the gorilla's conservation status, and to test these draft criteria with a worked example. Under the new criteria, if a species is likely to suffer a 50% decline in numbers in 100 years, it is categorised as ‘Vulnerable’. The gorilla species, one of its subspecies, and three countries' populations of gorillas are estimated to be ‘Vulnerable’, while Equatorial Guinea's and certainly Nigeria's populations are ‘Critically Endangered’ (80%, decline in the next 60 years). A crash in gorilla numbers is to be expected in the next century, until gorillas survive only in conservation areas, when continued survival will depend on degree of protection afforded. Four of the five IUCN criteria are exclusively demographic. However, demographic data are very difficult to collect; estimates of the rate of decline of habitat, which are notoriously unreliable, heavily influenced the categorisations; and modelling and data indicate that demographic criteria might sometimes be misleading. The feasibility of an ecological approach, in which the nature of the organism and how it uses its habitat is used to estimate risk, has been established for some species. Perhaps we need to concentrate more on developing a set of ecological criteria for use alongside the demographic ones.