Robert Paine was the first biologist to use the term keystone species in the 1960s. He was
studying food webs in the rocky, intertidal pools in the Pacific Northwest. At one of his study
sites, the dominant organisms in the tidal pools were mussels, barnacles, whelks, and a species
of starfish known as Pisaster ochraceus. To examine the relationship between these species,
Paine set up an experiment. In one area, he removed all the starfish from the tidal pools, and
in an adjacent area, he left the tidal pools as he found them. Prior to removing the starfish, he
sampled all the organisms in each pool. After two months, he repeated this sampling. A
summary of his results is illustrated in the graph below.
A
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What will be an ideal response?
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