1. U NDERSTANDING P OPULATIONS How Species Interact with Each Other

2. A N ORGANISM ’ S NICHE  Is a unique role of a species within an ecosystem  Can include the species’ physical home, environmental factors necessary for survival and all of the species’ interactions with other species  An organism’s habitat is a location  A niche is NOT the same as a habitat

3. W AYS IN W HICH S PECIES I NTERACT There are 5 major types of interactions: competition, predation, parasitism, mutualism and commensalism. These categories are based on whether each species causes benefit or harm to the other species in a given relationship.

4. C OMPETITION A relationship in which different individuals or populations attempt to use the same limited resource. Can occur both within and between species Species can compete even if they never come into direct contact with each other, this is indirect competition.

5. C OMPETITION C ONTINUED … One way to reduce competition between species is by dividing up the niche in time or space. Niche restriction occurs when each species uses less of the niche than it is capable of using. In the presence of competition, the actual niche used by a species may be smaller than the potential niche.

6. P REDATION An interaction where one organism feeds on another. An organism that feeds on another organism is called the predator. The organism that is fed upon is the prey. Most organisms have evolved some mechanisms to avoid or defend against predators.

7. P ARASITISM An organism that lives in or on another organism and feeds on it is a parasite. The organism the parasite takes its nourishment from is known as the host. Unlike predators, parasites usually do not kill their hosts. However, the host is often weakened or exposed to disease by the parasite.

8. M UTUALISM AND C OMMENSALISM A close relationship between two species in which each species provides a benefit to the other. Most organisms in a mutualistic relationship could not survive alone. A relationship in which one species benefits and the other species is neither harmed nor helped.

9. S YMBIOSIS AND C OEVOLUTION A relationship in which two species live in close association is symbiosis. Symbiosis is most often used to describe a relationship in which at least one species benefits. Over time, species in close relationships may coevolve. They may evolve adaptations that reduce the harm or improve the benefit of the relationship.