Laboratory 3: Symbiosis


In nature, organisms interact in a number of ways. We classify these interactions by two criteria: the effects of the interaction on the species involved, and the physical closeness of the interacting species. Predation, herbivory and competition are three of the most common interactions in which the species do not maintain long-term physical contact. In predation and herbivory, one organism benefits at the expense of another, as when a lion eats a zebra, or a caterpillar eats the leaves from a plant. In competition, resources needed by one species are also used by other species, adversely affecting growth, survival, or reproduction. Plants often compete for light, water, or soil nutrients, and animals sometimes compete for food or shelter.

Among the more fascinating interactions are those in which species maintain long-term, intimate associations. The general name for this interaction is symbiosis (Gr. sym=together, bios=life). Three types of symbioses are recognized, based on the effects of the interaction on the participants. Sometimes, however, it is difficult to tell what kind of symbiosis is taking place.