Summary
A species with a disproportionately large effect on its ecosystem relative to its abundance, like sea otters.
In depth
Robert Paine's starfish (Pisaster) removal experiment led to mussels excluding other species, cutting diversity. Sea otters, wolves, elephants and beavers (ecosystem engineers) are other examples.
Loss may cause cascading changes.
Keystone effects are disproportionate to abundance. They can be predators, engineers or mutualists. Identifying them requires removal or addition experiments.
Key idea: removing a keystone species changes the whole community.
Keystone species have effects out of proportion to their abundance. Paine's 1966 experiment on the Washington coast removed Pisaster starfish; within a year mussels dominated and species richness fell from 15 to 8. In Yellowstone, wolves changed elk behaviour, and the recovery of willow and aspen supported beavers and songbirds, although the scale of this cascade is debated. Elephants maintain savanna by knocking down trees, and prairie dogs create burrows used by many species.
Ecosystem engineers and foundation species are related categories: corals and kelp create habitat. Identifying keystone species is difficult and context dependent, but protecting them often benefits whole communities.
Frequently asked questions
What is Keystone Species?
A species with a disproportionately large effect on its ecosystem relative to its abundance, like sea otters.
Which area of biology covers Keystone Species, and how advanced is it?
Keystone Species is one of the 54 topics in Ecology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Trophic Cascade, Ecology, Species Diversity.
Why does Keystone Species matter?
Losing a keystone species can cause cascades of extinctions, which makes it a priority for conservation.
Can you give an example of Keystone Species?
Prairie dogs create burrows used by many species.
What should I learn before Keystone Species?
Work through the Beginner topics in Ecology first, such as Ecology, Ecosystem, Biotic and Abiotic Factors, then return to Keystone Species. Intermediate topics assume the Beginner vocabulary.
What topics are related to Keystone Species?
The closest topics to Keystone Species are Trophic Cascade, Ecology, Species Diversity, Limiting Factors. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Keystone Species?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Keystone Species. To practise the whole of Ecology, use the Ecology quiz.
How is Keystone Species different from Trophic Cascade?
Keystone Species: A species with a disproportionately large effect on its ecosystem relative to its abundance, like sea otters. Trophic Cascade: Top predator effects ripple down through lower trophic levels, as in wolves reintroduced to Yellowstone. Read both side by side and note what each one explains.
How should I study Keystone Species step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Trophic Cascade and explain the difference aloud. Finally, take the Ecology quiz and come back to this page for any question you miss.