What is a keystone species?
Keystone species play the same role in many ecological communities by maintaining the structure and integrity of the community.
keystone species have effects on communities that far exceed their abundance
keystone species influence the presence and abundance of other organisms through their feeding relationships.
The sea star P. ochraceus is considered a keystone predator,6 a single species whose impact on the whole community structure is disproportionately large relative to its abundance
A keystone species is a species that plays a critical role in maintaining the structure of an ecological community and whose impact on the community is greater than would be expected based on its relative abundance
Why is the sea star considered a keystone species in rocky intertidal habitats?
P. ochraceus feed on the mussel Mytilits californianus and, as a result, opens up spaces for other species
Of course predators consume prey, but in doing so, they may have broader impacts on communities as a whole. That is to say, predators help to maintain a balance among organisms, both by consuming prey and by altering prey behavior and prey habitat selection.
In what way does the presence of sea stars affect the diversity of organisms in the rocky intertidal? How do sea stars achieve that effect?
By altering competitive relationships, predation by Pisaster largely determines which species live in these rocky intertidal communites.
How does the removal of sea stars affect the rocky intertidal habitat?
An experiment was conducted to see how sever of an impact the removal of the starfish would have. The removal resulted in two major changes. First, the loer edge of the mussel bed extended farther down into the intertidal zone, showing that sea stars are able to eliminate mussels complately where they are covered with water most of the time. Second, and more dramatically, 28 species of animal and algae disappeared...
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