For Dung Beetles, Monkey Business Is Serious Stuff

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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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