More than half of the world's primate species are said to be endangered due to habitat loss.However, primates, including humans, have longevity, and it is difficult to investigate because the deterioration of the habitat does not immediately surface as a decrease in the number of individuals, and in fact there are few long-term observational studies.

The research group investigated the ecology of proboscis monkeys inhabiting the Kinabatangan region of Sabah, Borneo, Malaysia from 2004 to 2014.Proboscis monkeys are endemic to Borneo and are designated as endangered.At the same time, the Kinabatangan area has expanded its farms mainly for palm oil production, and more than 2000 hectares of forest, which is equivalent to about 9200 Tokyo Domes, have disappeared.

As a result of the survey, it was found that the total number of animals was maintained, but the number of individuals constituting one group decreased by about 1%.Previous primate surveys in Africa and South America have reported that the size of the herd initially shrinks and then the population declines as the condition persists.Proboscis monkeys may be approaching a similar condition.

Indonesia and Malaysia account for more than 8% of the world's palm oil production, and nearly 60 tons of vegetable oil are imported to Japan annually.As vast tropical forests are cleared and oil palm plantations expand for their production, many wildlife are being displaced from their habitat.Japan is also responsible for the threat of extinction of precious animal species.The Japanese government and related businesses in Japan need to take measures to develop sustainable oil palm plantations in the future.

Article information: [Oryx] Population dynamics of the proboscis monkey Nasalis larvatus in the Lower Kinabatangan, Sabah, Borneo, Malaysia