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 are 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 (starfish) from a section of the shore, aggressive mussels multiplied reducing the original 15 species assemblage to 8.

EFFECTS OF KS SPECIES Control potential dominants (sea otters control urchins that feed on kelp forests) Provide critical resources (certain fruit trees that provide a resource to a range of organisms at a time of scarcity)

Act as mutualists (fig wasps pollinate fig trees which provide a vital resource to frugivores who disperse seeds) Modify the environment (beavers building dams)

KEYSTONE SPECIES starfish sea otter gopher tortoise American alligator African elephant salmon beaver prairie dog

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."

Starfish 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