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SECTION
14.2
COMMUNITY INTERACTIONS
Reinforcement
Similar to how the interactions between you and your friends shape your relationships,
the way organisms interact in nature determines the dynamics of an ecosystem. Two
major interactions occur in nature:
• Competition occurs when two organisms fight over the same limited resources.
Competition can occur between individuals of the same species or between
individuals of two different species.
• Predation is the process by which one organism captures and feeds upon another
organism. Predation plays an important role in the adaptations of organisms to
their habitat.
In some cases, two species may have a very close relationship and interact with one
another very frequently. Symbiosis is a close ecological relationship between two
or more organisms that live in direct contact with one another. There are three main
types of symbiosis:
• Mutualism is an interaction in which both organisms get some kind of benefit. A
bee and a flower is an example of a mutualism. The bee receives food in the form
of nectar, and the flower is getting its pollen carried to another flower.
• Commensalism is an interaction in which one organism benefits, while the other
neither benefits nor is harmed. Small fish called remoras attach themselves to
the sides of sharks, and when the shark feeds, the remora eats the scraps the
shark cannot eat.
• Parasitism is a relationship in which one organism benefits while the other
organism is harmed. A leech may attach itself to a fish and suck the blood from
the fish. Eventually the fish will die, but the leech has kept itself alive on the
fish’s blood long enough to reproduce.
1. What types of resources might organisms compete for?
2. What are the three types of symbiosis?
3. What is the difference between parasitism and predation?
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Reinforcement
Unit 5 Resource Book
McDougal Littell Biology
Copyright by McDougal Littell, a division of Houghton Mifflin Company
CHAPTER 14
Interactions in Ecosystems
KEY CONCEPT Organisms interact as individuals and as populations.