The Macaque Shuffle

Some tales only the dead can tell. And thanks to the clever use of some chemical isotopes, biologists can now use dusty old museum specimens to reveal how massive biodiversity losses can shuffle the diet of the species that still survive.

Since the early 19th century, the city-state of Singapore has lost more than 95% of its primary forest. Researchers estimate it has also lost 34% to 59% of all bird species, and 42% to 78% of all mammals, Luke Gibson of the National University of Singapore reports in the journal Primates. The long-tailed macaque (Macaca fascicularis) is one of two remaining primates on the island, and some 70% of the less than 1500 remaining macaques now live in nature reserves.

To see how Singapore’s massive ecological changes may have affected macaque feeding behavior, Gibson took hair samples from eight live macaques, and from six skins from macaques collected in Singapore between 1893 and 1944 that are now preserved in the Raffles Museum of Biodiversity Research. Then, he measured the ratios of certain carbon and nitrogen isotopes in the hair; the isotopic composition is heavily influenced by what the animals have eaten.

It turned out the carbon ratios were essentially the same in the animals from the two time periods – meaning both the dead and living animals foraged in the same kind of habitat. The nitrogen ratios, however, were different, indicating that modern macaques have shifted their diets. In particular, the data suggested the animals were now feeding at a lower “trophic level” – or lower down on the food chain – than they had in the past.

“This decline in trophic level may be because of the disappearance or decline of other species that compete with macaques for fruit,” Gibson writes. “Macaques consume mostly leaves, seeds, and fruit supplemented with some invertebrates and vertebrates, and increased fruit abundance may cause a proportional decrease of invertebrates and small vertebrates in their diet.”

The study “highlights the effect of continued habitat modification and associated biodiversity loss on animal communities,” Gibson concludes. “The ability of species such as the long-tailed macaque to persist despite extensive forest degradation may be possible because of their ability to alter their behavior.” And since macaques are now one of the most-widespread non-human primates, “their persistence in degraded forest habitats may be critical to the preservation of key ecosystem functions such as seed dispersal, in Singapore and beyond.”David Malakoff | May 31, 2011

Source: Gibson, L. (2011). Possible shift in macaque trophic level following a century of biodiversity loss in Singapore. Primates DOI: 10.1007/s10329-011-0251-9

Image © Sunsetman |