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Zoo-Ology: Togetherness (Symbiosis)

By Victoria Advocate
June 19, 2011 at 1:19 a.m.

A clownfish swims among a sea anemone's tentacles.

By Judie Farnsworth

Symbiotic relationship. Many people describe this as two different species interacting beneficially; bees pollinating flowers and birds dispersing seeds. Right!

But there are other symbiotic relationships and some are not all sunshine and roses.

Mutualism - This is the bee and the flower, the bird dispersing seeds. A win-win situation where both species benefit.

How about Nemo - a clownfish protected from predators by living among a sea anemone's tentacles. He does his part by defending against anemone-eating fish.

A bird (Egyptian plover) actually cleans decaying meat stuck in a crocodile's teeth. The crocodile lies with its mouth open; the bird flies in for dinner and incidentally, some dental work. The croc doesn't eat the bird - amazing!

Commensalism - One species benefits, but the other is neutral: hermit crabs using empty gastropod shells, birds following cattle or horses to catch insects stirred from the grass. Ball moss (actually a bromeliad) attaches to trees with pseudo-roots, but doesn't remove water, minerals or anything else. Barnacles growing on whales have a place to stay, a taxi service and occasional munchies (whales can be messy eaters).

Some biologists argue that commensal interactions may not be totally neutral. For example barnacles appear to be basically hangers-on, but what if they become too thick? There is that potential. So, are they neutral or does the relationship belong in another type of symbiosis? Read on.

Parasitism - One species benefits, but the other is harmed. Ticks or fleas on animals or people are prime examples. Plants can have, or be, parasites. Mistletoe is a partial (hemi) parasite. It can grow on its own but is usually found on a host tree.

Unlike ball moss, it sends roots into the tree to take nutrients.

Brood or social parasites are found in the bird, fish and insect world. Have you seen a bird, maybe a cardinal, feeding a large youngster that didn't seem to belong with it? Junior was most likely a cowbird or cuckoo. Those species don't build their own nests.

A female will lay an egg in another bird's nest and abandon it. She may remove the other bird's eggs before making her getaway. After the counterfeit egg hatches, the growing not-so-little one gets most of the food or may push any other babies out of the nest entirely.

Mutualism, Comensalism and Parasitism. That's just the beginning. There are countless levels of actions and interactions, which can seem hugely complex and many unanswered questions remain.

Given everything living and growing in our ecosystems; land, marine, the vast world of lichens, algae, microorganisms and bacteria the complexities can be mind boggling, but are more incredible than any sci-fi movie.

Judie Farnsworth is a long time volunteer at the Texas Zoo specializing in educational programs.

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