A tick may live in a dog's ear. A cattle egret may eat insects disturbed by walking cattle. In this lesson we will study three different types of relationships in which two organisms of unlike species live together in close association. We will learn many examples of each type. Symbiosis is the living together in close association of organisms of two different species.
Mutualism is a close relationship between two organisms which is helpful to both organisms.
Parasitism is a symbiotic relationship in which one organism, the parasite, spends much or all of its life in or on another organism, the host. The parasite is dependent upon the host for food. The parasite benefits from the relationship, and the host is always harmed. Commensalism is a symbiotic relationship in which one organism is helped and the other is neither helped nor harmed. The major purpose of this activity is for students to become familiar with the concept of symbiosis as one example of interdependence in ecological systems.