Environmental Science / Unit 3: Biomes and Biodiversity
3.4 Keystone and Other Special Species
Notes
Some species matter more than their numbers suggest.
- A keystone species has a large effect on its ecosystem relative to its abundance. Removing it changes the whole community.
- Examples: sea otters eat sea urchins, which protects kelp forests; wolves in Yellowstone control elk and let trees recover; beavers build dams that create wetlands.
- An indicator species shows ecosystem health (frogs and lichens are sensitive to pollution).
- A foundation species (such as coral) creates the habitat for others.
- An invasive species is a non-native species that spreads and harms native species, often because it lacks natural predators.
- An umbrella species is one whose protection also protects many others that share its habitat.
- Example: when sea otters are removed, urchins boom and destroy kelp forests.
Practice
Sea otters eat sea urchins, which graze on kelp. When otters are removed, urchins multiply and destroy kelp forests. Sea otters are an example of a:
Their effect on the ecosystem is far larger than their numbers suggest.
Frogs are often studied because their thin skin makes them sensitive to pollution. This makes them useful as:
A decline in an indicator species signals environmental problems.
Why do invasive species often spread quickly?
Without natural controls, their numbers can grow rapidly.
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