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KEYSTONE SPECIES
• KEYSTONE - the
central stone of an
arch or vault.
• It is the most
important stone in an
arch bridge, without
this stone the arch
would collapse.
DEFINED
• A keystone species
is one whose
impact on its
community or
ecosystem is larger
and greater than
would be expected
from its relative
abundance or total
biomass.
• The term “keystone” was coined by Robert
Pain and was based on his studies of
rocky shore communities in California.
• When he removed a top predator (sea
star) from a section of the shore,
aggressive mussels multiplied reducing
the original 15 species assemblage to 8.
EFFECTS OF KS SPECIES
1. Control potential dominants (sea otters
control urchins that feed on kelp forests)
2. Provide critical resources (certain fruit
trees that provide a resource to a range
of organisms at a time of scarcity)
3. Act as mutualists (fig wasps pollinate fig
trees which provide a vital resource to
frugivores who disperse seeds)
4. Modify the environment (beavers
building dams)
KEYSTONE SPECIES
1.
2.
3.
4.
5.
6.
7.
8.
9.
Sea star
Sea otter
Gopher tortoise
American alligator
African elephant
Salmon
Beaver
Oyster
Horseshoe crab
NOT KEYSTONE SPECIES
•
•
•
•
trees
giant kelp
prairie grasses
reef-building corals
Not KS species because their impact on
the ecosystem is proportional to their
biomass.
IMPORTANCE OF KEYSTONES
“Its importance," says Paine, "is that it
convinced managers and conservationists
alike that the ecological impact of single
species matters. That is, in order to
manage, understand, and restore
ecological assemblages, the roles of
individual species have to be understood
and considered."
Sea Star
• Keeps predatory mussel populations in
check
Sea Otter
• Keeps urchins from consuming the kelp
forest
Gopher Tortoise
• Tortoise burrows provide shelter for more
than 360 species of mammals, birds,
reptiles and amphibians
• Species which utilize the burrows include
skunks, opossums, rabbits, armadillos,
Florida mice, burrowing owls, quail, indigo
snakes, gopher frogs, snakes, lizards,
frogs, toads, and over 300 invertebrates
• These species are commensalistic and
use the burrows to escape fire, weather,
predators, etc.
• Some species are dependent on the
burrows
American Alligator
• Alligators dig holes which provide habitat
for many other species
African Elephant
• Scarafication
• Many plant species are dependent on
passing through an elephant’s digestive
tract before they can germinate. It is
calculated that at least a third of tree
species in west African forests rely on
elephants in this way.
Elephant Extras
• They modify their habitat by converting Savannah and
woodlands to grasslands
• Elephants can provide water for other species by digging
water holes in dry riverbeds
– the depressions created by their footprints and their bodies trap
rainfall
• Elephants act as seed dispersers by their fecal matter. It
is often carried below ground by dung beetles and
termites causing the soil to become more aerated and
further distributing the nutrients
• Their paths act as firebreaks and rain water conduits
• An Elephants journey through the high grass provides
food for birds by disturbing small reptiles, amphibians or
insects.
Salmon
• 137 species have been documented to
depend on salmon
• 41 are mammals including killer whales,
bears and river otters
• 89 are birds, including bald eagles,
Caspian terns and grebes
• five are reptiles and two are amphibians.
Salmon Con’t
• Several species depend on salmon both
directly and indirectly—feeding on salmon
as well as preying on species that eat
salmon
• Many insects feed on salmon, and then
become food for juvenile salmon
• No less than 82 species feed directly on
salmon carcasses
Beaver
• Beaver dams serve to create wetlands and
ponds.
• The benefits to humans include: flood
control, removal of pollutants, drought
protection and decreased erosion
• American Indians called the beaver the
“sacred center” of the land b/c this species
creates rich habitats for other mammals,
fish, turtles, frogs, birds, and ducks
Prairie Dog
• Black-tailed prairie dogs play an integral role in
the prairie food chain
• They are a critical food source for such animals
as the endangered black-footed ferret, swift fox,
coyotes, hawks, eagles and badgers
• Their burrows act as homes to other creatures,
including burrowing owls, badgers, rabbits,
black-footed ferrets, snakes, salamanders, and
insects.
• Their burrowing activity works to loosen and
churn up the soil, increasing its ability to sustain
plant life
Horseshoe Crab
The horseshoe crab Limulus polyphemus is not a
crab at all, but is more closely related to spiders
and scorpions. It has changed little in over 300
million years, and the Delaware Bay is home to the
largest population of spawning horseshoe crabs in
the world. Each spring the warming waters bring
the crabs from the Delaware Bay and Atlantic
Ocean to the coastlines of New Jersey and
Delaware. In late spring, at the high tides of the full
and new moons, female crabs come ashore to lay
their eggs, depositing up to 20,000 small eggs in
shallow nests in the sand.
At the same time the horseshoe crabs are laying their
eggs, nearly a million shorebirds converge on the
Delaware Bay each spring on their northward migration.
The Bay is the second largest feeding stopover in the
western hemisphere for north-bound shorebirds. Many
of these shorebirds travel thousands of miles nonstop
from Central and South America. They arrive thin and
hungry and rely on the feast of tiny green horseshoe
crab eggs to regain their weight and energy reserves for
the rest of their trip to summer nesting grounds in
Canada and the Arctic.
As many as 30 species of shorebirds cram the shoreline
in late May trying to double their body weights. The four
most common species are the red knot, sanderling,
ruddy turnstone, and semipalmated sandpiper.
Horseshoe crab
Limulus polyphemus
https://www.youtube.com/watch
?v=QFiYVJBBkws
Eastern Oyster
Crassostrea virginica
• Without oysters many coastal ecosystems
would collapse. Each oyster can filter up to
50 gallons of water per day. A healthy
oyster bed can dramatically improve
water quality, in addition to cycling water
between the water column and bottomdwelling species.
• Provide valuable shelter and habitat for
many other estuarine organisms, improve
water quality, and reduce bank erosion.
https://www.youtube.com/watch
?v=90LTtKIFY8U
Gotta love a horseshoe crab!
https://www.youtube.com/watch
?v=ysa5OBhXz-Q
Grand finale