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A keystone species is a species
that has a disproportionately

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strong effect on the health and 
functioning of its ecosystem.

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Identifying and studying keystone species

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can be useful in studying and 
preserving the health of an ecosystem

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Here's two examples of keystone species.

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Reintroducing wolves
in the greater Yellowstone ecosystem

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had cascading positive effects

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on plant populations, on soil health,

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in all the processes
that depend on both.

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And restoring sea otters 
along the Pacific Coast of North America

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depressed populations of marine 
herbivores and predators,

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which allowed other species to recover.

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Keystone species are 
not just limited to charismatic mammals.

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Effectively any organism 
in an ecosystem could be keystone.

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The critical characteristic
of a keystone species

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is that a large portion of the flow of 
energy and sources through an ecosystem

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depends on that species.

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This can occur when the species
consumes resources itself,

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or promotes or inhibits the 
consumption of resources by others.

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Consider the north american 
coastal redwood

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Not only does this tree 
provide raw sources of carbon

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for other organisms to consume

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it also alters the local climate.

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Increasing moisture, 
building organic rich soils

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and providing a complex substrate

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for other organisms to live in

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from bryophytes to birds to insects to 
microorganisms.

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In effect, redwoods create
ecosystems within ecosystems

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That's how highly connected they are 
within the network of

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all biological interactions
along the Pacific Coast

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These species and many others
were discovered by accident

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by misguided human actions
leading to their removal.

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Resulting in negative downstream
consequences due to their absence.

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But it doesn't have to be that way.

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Tools from Network Science now allow us to
identify keystone species

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using information about the interactions
that connect members of an ecosystem.

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Such as when on spices feeds on another
or relies on another for its survival.

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Using this network approach we don't have
to wait for the accidents to realize

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what drives the ecosystem health.

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Understanding keystone species
can help us explore ways

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to restore biodiversity that sustains us.

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And here, at the Santa Fe Institute
we'd like to apply concepts

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across disciplinary boundaries so we can
use the idea of keystone species to

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understand how innovations revolutionized
economy or how life itself began on earth.