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For Dung Beetles, Monkey Business Is Serious Stuff

John Roach
for National Geographic News
May 26, 2004
 
Monkey see, monkey eat, monkey doo.

So the seeds of the Amazon's much-lauded biodiversity are spread around the rain forest, in many cases. And where there's monkey business, so too are dung beetles, according to Kevina Vulinec, an assistant professor of wildlife ecology at Delaware State University in Dover.

The dung beetles, as their name suggests, make a living off other animals' waste. In the process they sow whatever seeds make it through the treasure-dropping animals' digestive tracts.


"Dung beetles are essential to tropical biodiversity, and they may be more essential than we even know," said Vulinec, who studies the interactions between monkeys and dung beetles. His aim is to understand their roles in seed dispersal and thus tropical biodiversity.

Of particular interest to Vulinec are the applications of this line of research to conservation efforts aimed at regenerating areas of the Amazon rain forest that have been cleared for agriculture and ranching.

Alejandro Estrada, a wildlife ecologist the Universidad Nacional Autóoma de México in Veracruz, said "studies in several neotropical forests have shown that in the natural process of rain forest regeneration, the primate-dung beetle-plant interaction plays an important role."

Seed Dispersal

A piece of fruit may not fall very far from its parent tree. But in the Amazon the seeds in the fruit need to get as far away as possible if they want to stand a chance at survival.

"If the seeds don't get away from the parent tree, they are susceptible to all the diseases the parent tree has," Vulinec said.

In 1928 auto magnate Henry Ford learned this lesson the hard way. He established a rubber plantation in Brazil so that he could wrest full control of the rubber used for his car business from a cartel based in the Netherlands' Asia colonies.

The plantation, including the imported, prefabricated town of Fordlandia, was a flop. "Within a couple of years, [the rubber trees] all got the blight and were all wiped out," Vulinec said. "The whole project went bankrupt."

Ford's problem was that he planted all the rubber trees right next to each other. Rubber plantations created with Brazilian rubber-tree seeds took root and flourished in Malaysia, where there is no blight. But rubber trees only grow in Brazil when separated.

In the natural rain forest, this separation of rubber trees is easily produced, thanks to the unknowing help of seed dispersers such as monkeys and dung beetles.

Monkeys are what are known as primary dispersers. They eat the fruit at one tree, swing from tree to tree for about a day and then defecate, leaving the undigested fruit seed in a steamy pile on the ground.

Dung beetles, which are considered secondary dispersers, then swarm the steamy pile and go about their business of making a living.

There are thousands of different kinds of dung beetles that go about their dung-pile business in a variety of ways. "The dung beetles that are important, in terms of secondary seed dispersal, are the rollers and the tunnelers," Vulinec said.

The rollers make a ball out of the dung and roll it away. They bury it to eat later or lay eggs in it, so that their larvae will have a meal when they hatch. The tunnelers, or burrowers, dig a hole directly beneath the dung pile, where they then bury the dung and do with it as they please.

"Inadvertently seeds are buried as contaminants of the feces," Estrada said. "Because of this, many seeds escape predation by ground-living, seed-eating mammals like rodents, and some may germinate and become established as seedlings on the forest floor."

So how much dung can a dung beetle handle?

While there are no hard facts, Vulinec said that a few years ago she and her colleagues happened upon a three foot by three foot (one meter by one meter) dung pile deposited below a tree branch by a troop of howler monkeys in a "group poop."

"[They] all get together, go out on a limb away from the sleeping tree, and all poop together and cause this enormous pile of dung," Vulinec said.

Amazed when they happened upon such a pile, the researchers measured it. The next day they planned to use it to bait their traps, but when they got back to the site of the pile, the only thing left was two dung beetles fighting over the last two balls.

Conservation Strategy

Vulinec's most recent research is focused on the interactions between monkeys and dung beetles at different forest types in the Amazon. It is an attempt to understand the potential for natural reforestation, given the communities of seed dispersers present.

She and her colleagues have found that in areas flooded by river waters, known as várzea forests, rollers dominate. Forest areas not flooded by river waters, known as terra firma, are dominated by the burrowers.

"So the seeds in the terra firma forest are more likely to get buried deeply in clumped patterns than seeds in várzea areas," Vulinec said.

By knowing what types of dung beetles prefer what types of habitat, conservationists can understand whether or not the dung beetles would be efficient seed dispersers in habitats that need regeneration, of which there are many in the Amazon.

While thousands of acres of Amazon rain forest are cleared each year to make room for crop growing and cattle grazing, the forest soils can only sustain such practices for a few years. Then they are abandoned.

Vulinec's research shows that if such abandoned lands are adjacent to undisturbed primary forest, monkeys will flock to the secondary forest as it begins to grow. "And if you have monkeys, you will have dung beetles," she said.
 

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