Wednesday, January 29, 2014

A Sloth's Self-Made Food Web

Sloths move sloooowly and maybe now we know why: they eat algae from their own coat. So no need (or ability) for speed to chase animal prey or to travel far to find food. The algae is right there, on their body, and it leaves a green-tint to the sloth's fur.

A three-toed sloth moves slowly on the ground,
Panama 1983 (photo by Ellen Snyder)
The three-toed sloth carries around an entire ecosystem, which includes the sloth, a moth, fungi and bacteria, and a species of algae. This comes via research by University of Wisconsin biologists highlighted in a New York Times article by Nicholas Wade.

The three-toed (actually better described as three-clawed) sloth lives in tropical trees, in Central and South America. I saw these tree-dwelling mammals in Panama in 1983. While there I witnessed the once-a-week ritual when the sloth climbs down from its tree perch to defecate. At the time I did not appreciate the complexity of the sloth's living arrangement. Although I knew it liked to hang from its favorite tree.
A sloth hangs from its favorite tree
Panama 1983 (photo by Ellen Snyder)
Biologists used to think that the green coloring on a sloth's fur was for camouflage, to hide it from its main predators--a jaguar on the ground or a harpy eagle from above. But now it seems that the sloth maintains its own mini food web that includes the green algae.

A species of moth lives in the sloth's fur coat. When the sloth climbs down from the tree every week or so to relieve itself, the accompanying pregnant moths lay eggs in the fresh dung. The moth caterpillars hatch and feed on the dung, rather than on plant material like most caterpillars. Eventually, after the larvae turn into adult moths, they flutter up to find the sloth host and a mate. Some of the moths die (probably all the males) and decompose on the sloth, helped by fungi and bacteria that also live there. The by-products of the decaying process, including nitrogen, feed the algae, which in turn is eaten by the sloth.

Now that is a cool story to warm your body on a cold winter day.

A sloth climbs down to the ground--a once a week ritual
Panama 1983 (photo by Ellen Snyder)

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