Warner Corner - June 2008

You Scratch My Back, I'll Scratch Yours
Bekah Dalen, Interpretive Naturalist

The Merriam-Webster dictionary defines the word symbiotic as "the living together in more or less intimate association or close union of two dissimilar organisms." Hmm...sounds like marriage. But that's for another article. Today I want to talk about relationships in the natural world. Symbiotic relationships are found all throughout nature and they come in many different forms. Ecologists have generally defined three types of symbiotic relationships:

• Mutualism - both species benefit from the relationship
• Commensalism - one species benefits, the other is unaffected
• Parasitism - one species benefits, the other is harmed

Because I am in a cheery mood, let's focus on the friendliest of all these relationships - mutualism. Take the shining example of flowering plants and pollinators. Most flowering plants need help transferring their pollen from one flower to another. If the pollen cannot be moved by wind, then the flower requires a pollinator. Pollinators, such as bees and hummingbirds, need food to survive and they get that food, usually nectar or pollen, from flowers. The pollinators provide an important service to the flowering plants while the plants provide food to the pollinators. Both species benefit. Another common example of mutualism is the relationship between oak trees and squirrels. The squirrels gather acorns in the fall and burry them throughout the forest. In the winter they dig them up for food. Not all the acorns are recovered, however. Some are forgotten in the soil and grow into new oak trees. The oak give up some acorns for food and in return the squirrels plant a few to carry on the species.

You've probably heard about these relationships before, but what about ants and aphids or fungus and plant roots?

Ants and Aphids
Certain species of ants and aphids have a very interesting mutualistic relationship. Some ants are best known for being "aphid farmers" as they tend to aphids similar to the way people tend to livestock. They protect the aphids from predators and carry them from stem to stem to feed on fresh plant juice. They even take the aphids to a safe spot to hunker down for the night. Why do they do this? The aphids secrete a sugary substance called honeydew, which the ants eat. Delish.

Fungus and Plant Roots
This cooperative relationship is so beneficial that an estimated 90% of plants have mutualistic symbiosis with fungus. Here is how it works. Tiny strands of fungus, called hyphae, spread throughout the soil absorbing minerals. They sometimes wrap around or even enter roots of trees and other plants. This association, called a mycorrhiza, allows the plant to absorb minerals collected by the fungus while the fungus takes in sugars produced by the plant through photosynthesis. This relationship allows each organism to do what it does best and share its bounty with the other.

Now before you go thinking that humans have been left out of nature's "you scratch my back I'll scratch yours" symbiosis, here is one organism that helps us out from time to time...bacteria. Studies show that certain bacteria may help us digest our food (think of the bacteria sometimes used in yogurt) and protect us from disease. In return, we give them nourishment and a warm, moist place to grow. Not a bad deal!