SYMBIOSIS A close nutritional or other relationship between two organisms.
MUTUALISM A relationship in which both organisms benefit.
Examples: A bee and flowering plant. A pilot fish and shark. Bacteria in plant roots. Clown fish, sea anenome.
Examples: A remarkable 3-way mutualism appears to have evolved between an ant, a butterfly caterpillar, and an acacia in the American southwest. The caterpillars have nectar organs which the ants drink from, and the acacia tolerates the feeding caterpillars. The ants appear to provide some protection for both plant and caterpillar. Research of Diane Wagner, American Museum of Natural History Southwestern Research Station
Parasitism One organism (parasite) benefits, the other (host) is harmed.
Examples: Tape worms, hook worm, heart worms.
In the photo, a tomato hornworm is covered with cocoons of pupating braconid wasps. The braconid wasp is considered a parasitoid of the hornworm because it causes the hornworm to die as it pupates. By the time the wasps undergo metamorphosis, all of the hosts insides have been digested, thus by the time they are ready to pupate, the caterpillar will die. While this may be detrimental to the tomato hornworm, it is considered beneficial for gardeners...as the tomato hornworm can be a signifant pest. Parasitism usually connotes a negative feeling; however as seen in this case, it can be considered beneficial.
Dog heartworm
Commensalism One organism benefits, the other is unaffected.
Examples: Barnacles on a whale. Moss on a tree.
Barnacles adhering to the skin of a whale or shell of a mollusk: Barnacles are crustaceans whose adults are sedentary. The motile larvae find a suitable surface and then undergo a metamorphosis to the sedentary form. The barnacle benefits by finding a habitat where nutrients are available. (In the case of lodging on the living organism, the barnacle is transported to new sources of food.) The presence of barnacle populations does not appear to hamper or enhance the survival of the animals carrying them.
SUMMARY