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Symbiosis
Organisms in an ecosystem interact in many different ways. One very common relationship is that of
predator to prey (which we have covered extensively). Another type involves long-term, intimate
association between two different species: symbiosis. Below are brief descriptions of three types of
symbiotic relationships.
 Commensalism is a relationship in which one partner benefits while the other is neither harmed
nor benefited.
 Mutualism is an association in which both members benefit.
 Parasitism is a widespread nutritional strategy in which one member of the couple harms the
other. The exploiting member is the parasite, the other is the host.
The following situations illustrate various ecological relationships. Identify which relationship is being
described in each situation (commensalism, mutualism, parasitism, or predation).
1. Mites (8 legged organisms similar to spiders) live in the base of eyelashes of people who use
mascara; they do not seem to harm people. __________________
2. A coyote captures, kills, & eats a rabbit. __________________
3. A tapeworm lives in the intestines of dog. It absorbs the food the dog has eaten & grown larger in
the process. The dog becomes weak from malnutrition. __________________
4. Birds eat insects that the hooves and muzzles of grazing cows disturb. __________________
5. The flower of the yucca plant provides the only location where the yucca moth can lay her eggs. In
the process, the moth pollinates the yucca flower. __________________
6. Cleaner Shrimp living in the ocean eat ectoparasites off the surface of fish. __________________
7. Bacteria that live on the surface of our teeth require sugar from our food to survive. A by-product of
their metabolism decays the enamel of teeth. __________________
8. A 6 point buck is killed by a hunter. __________________
9. Bacteria in the intestines of cows produce vitamin C, enabling cows to skip orange juice for
breakfast. __________________
10. Nitrogen-fixing bacteria live in the roots of some plants. They provide nitrogen in a form that plants
need and obtain a “home” & nourishment from plants. __________________
11. Nematodes (a round worm) live in plants & gain nourishment from the plant, but do not seem to
harm it. __________________
12. E. coli lives in massive quantities in the large intestines of humans. They produce vitamin K which
aids in blood clotting. (It is unknown if this vitamin is absorbed here though.) __________________
13. Aspen trees provide shade for small spruce and fir trees, which do not do well in direct sunlight.
__________________
14. Insects lay eggs in the buds of spruce trees. The insect larvae live off the plant material and
prevent the bud from developing normally. __________________