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I can identify the types of relationships that occur among populations in a community.

Learning Standard:

LS-13:  Give examples of ways in which organisms interact and have different functions within an ecosystem that enable the ecosystem to survive.

Main Ideas:

Symbiosis refers to any close relationship between two or more different organisms in which the organisms live together for extended periods of time.  There are three types of symbiotic relationships:



A symbiotic relationship that benefits both species.  The relationship helps each species survive through the challenges of mother nature and adapt for future generations.

An example of mutualism is the relationship between the Egyptian plover and the African crocodile.  In the tropical African jungles, the crocodile allows the plover to fly into its mouth to eat the decaying meat stuck in the crocodile’s teeth.  The crocodile gets its teeth cleaned and the plover gets a free meal.  In this way, both organisms benefit from each other.  “The feeling is mutual.”

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A symbiotic relationship where one species benefits from the relationship, while the other remains unaffected.

An example of commensalism is the relationship between the sea anemone and the anemone crab.  The anemone crab is immune to the sting of the sea anemone and finds protection within the anemone’s swaying arms.  The sea anemone is neither harmed nor helped by the crab.



A symbiotic relationship that benefits one organism (the parasite) and does definite harm to the host organism.

An example of parasitism is the relationship between some cordycep fungi and certain insect species, such as ants and caterpillars.  The cordycep spores infect the host organism and take control of the host’s brain.  Eventually, the cordyceps will grow and erupt out of the host organism.  Not all parasites kill their hosts, however, all parasites do cause harm to the host organism.

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