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A green equilibrium fosters a new behavior in Sri Lanka

By Christopher Wills


The balancing act that keeps ecosystems intact results from interactions, not only among the animals and plants, but also among their many smaller pathogens, parasites, symbionts, and pollinators. Taken together, all these interactions among the visible and invisible world produce an ecological balance, a green equilibrium.

I traveled to Sri Lanka to visit colleagues who are working in a tropical rainforest. While I was there I visited Bundala, a bird sanctuary in the southern part of the island. Bundala’s green equilibrium has produced an unusual cross-species cooperative interaction that also depends on the invisible world. If you paddle around a coral reef, you will often see tiny fish or shrimp removing and eating parasites from the mouths and gills of larger fish. The large fish, which are sometimes fierce predators, go to specific regions of the reef known as cleaning stations. There they temporarily shelve their aggressive behavior while the small fish operate on them.

Such clearly cooperative behavior across species boundaries is common in the marine world but less obvious on dry land. Oxpecker birds, which clean parasites from the ears and nostrils of large grazing animals in East Africa, often stray over the line between beneficial symbiotic and harmful parasitic behavior. They can actually prey on the slow-moving grazers, opening wounds and drinking their blood.

At Bundala I was lucky to see a much clearer example of dry-land cross-species cooperation. In an open area fifty yards from our truck, a black-naped hare crouched down and half-closed its eyes while a common mynah walked across its back and plucked clearly visible ticks from its ears. My camera equipment was just adequate enough to get pictures. In Brazil, jacana birds have been photographed removing ticks from the tummies of capybaras, but so far as I know this is the first time such unequivocally cooperative behavior has been photographed outside of South America.

For this behavior to happen, there must be so many ticks in the park’s grassland that the hares, tormented by their itching, will permit the birds to administer a painful remedy. And the hares and mynahs must interact with each other often enough that trust can build up between them. We saw many jackals nearby, so the cooperative behavior must take place in open areas where the hares are safe.

The hares, mynahs, jackals and ticks have together shaped this remarkable interaction. Bundala’s green equilibrium is providing opportunities for such complex equilibria to evolve, opportunities that will be lost if we damage this precious ecosystem.

Christopher Wills is a Professor Emeritus, Section of Ecology, Behavior and Evolution at the University of California, San Diego. He has published numerous books including The Darwinian Tourist and the soon to be released Green Equilibrium: the Vital Balance of Humans and Nature.

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Image Credit: Copyright Christopher Wills. Do not reproduce without permission.

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