Parasites Can Help the Ecology

A parasitologist suggests that parasites don’t just rob and steal; they usually do good as functional players in an ecosystem.

Maybe it’s because Tommy Leung is a parasitologist that he can see the good in anything, but in The Conversation, the lecturer on parasitology and evolutionary biology lists 3 examples of good things that creatures we might find repulsive do to help the community of organisms.

• A tiny worm helps stream fish feed on nutritious crickets by getting the bugs to jump into the water.  He calls this a kind of “fast food delivery service” that provides half the fish energy intake in some watersheds.
• A fluke that infects shellfish helps deposit them on seashores where birds can eat them, and barnacles and limpets and live in the shells – increasing the biodiversity of a shore that would normally have only sand.
• Mistletoe increases leaf litter in a forest, without which bird diversity decreases by 25%.

“Parasites are thought of as free-loaders, but many contribute as much as they take,” Leung says. “They service the ecosystem. From an ecological perspective, they are more like tiny, hidden architects that are overlooked by most people.”  The nasty parasites, he claims, have an explanation: “Some parasites do have a negative impact on an ecosystem, especially when they are introduced to a new and unfamiliar environment.”

Leung’s short essay, though filled with spelling errors, is thought-provoking.  It adds to growing evidence that our categories of natural evil need rethinking (see also our 2/04/12 entry, or search on “parasites” in the search bar).  This is not to minimize the pain and suffering human parasites cause, or to suggest we should not seek to eradicate those that cause harm.  But it wouldn’t make sense from either an evolutionary or design perspective if a parasite killed off all its hosts, would it?  Then the parasite would perish with its vehicle, while the host proliferated without checks and balances.  This is similar to predation; the predator helps prune the prey population, while taking benefit for itself at the same time.  It’s a bit like a market economy: you only earn a profit if you provide a valuable service.

Creationists see a functional ecosystem as evidence of design, but it’s a design fit for a fallen, sin-cursed world.  Maybe we need to step back and see the big picture before casting judgment.  Since crickets will die anyway, and have no spirit, why not use some of them for a fast-food delivery service for fish, if it will benefit the ecology as a whole?  Aren’t people predators on animals, too?  The Bible teaches God can turn evil for good; maybe some of these are living illustrations.  Would you have considered parasites as “tiny, hidden architects” of biodiversity that run a service business?  Human beings, as caretakers of the world, should avoid mucking things up by introducing parasites where they cause only harm to the ecosystem, or where they cause pain and suffering to the environmental stewards God created in his image to “care for the garden, and keep it.”  It’s a garden with thorns and sweat, but it’s still an intelligently designed garden.