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Keystone species are those that play a unique and crucial role
in ecosystem function.
They have a disproportionately large effect on their environment relative
to their abundance.
Because of their key role in maintaining biodiversity
efforts to manage and protect keystone species
can help stabilize the entire biological community.
The term keystone species was first coined by Doctor Robert Paine
in 1969.
His research found that the purple sea star prevented mussels from over-
populating rocky intertidal ecosystems in the Pacific Northwest.
There are five generally recognized categories of keystone species --
keystone predators, modifiers,
prey, mutualists, and hosts.
If a keystone predator like the gray wolf is removed from the ecosystem,
populations of their prey such as elk exponentially increase.
This can cause a cascading effect on other plants and animals within
the ecosystem.
By preying on mussels that would otherwise dominate the ecosystem, the
purple sea star is a keystone predator that opens up habitat for a diversity
of other species.
Another keystone predator is the American alligator found in the
southeastern U.S.
Alligators prey on fish, amphibians, reptiles, birds, and mammals
The alligator is also an example of a keystone modifier, or ecosystem engineer,
which creates or significantly modifies its habitat.
Alligators dig depressions in the ground that fill with deeper water providing
refuge for fish and other aquatic species during the dry season.
Another keystone modifier is the black-tailed prairie dog,
which keeps grassland in the Great Plains properly maintained with a
diversity of plants that benefit other grazing species such as cattle
and pronghorn.
Prairie dog burrows aerate compacted soil and allow water to penetrate
deeper into the ground.
Many other species use the burrows for shelter.
Prairie dogs are also an important food source for coyotes, foxes, hawks, and the
endangered black-footed ferret.
That brings us to the next category,
keystone prey, which can cause significant fluctuations in predator
densities.
Pacific salmon are keystone prey playing a vital role in Pacific Northwest
ecosystems
and directly benefiting eighty-nine birds,
forty-one mammals,
five reptiles, and two amphibians through ecosystem nutrient loading.
The black-bellied salamander is another keystone prey species that provides a
large amount of protein biomass for predators in certain stream
ecosystems in the southeastern U.S.
Keystone mutualists are those organisms that participate in mutually
beneficial interactions, with hummingbirds the most notable examples.
Otherwise known as link species,
many hummingbirds pollinate highly specialized plants adapted o
pollination only by these birds.
The last category is the keystone host, with the quaking aspen being one example.
Aspens create an open canopy that harbors diversity on the forest floor,
attracting many insects not found elsewhere within the ecosystem.
In addition, the red-naped sapsucker,
a keystone modifier
excavates its nests in aspen trees.
The abandoned nests provide shelter for many other bird species.
The greater biodiversity that keystone species help maintain affords protection
of water resources and soil,
nutrient storage and recycling,
pollution control, and better recovery from unpredictable environmental events.