Keystone Species and Their Role in Ecosystems

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.

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