Find the keystone by what happens when it's gone
- The idea
- Predict
- See it
- Why
- Check
The idea
“The keystone is the most common species, or the biggest one, or the one at the top of the food chain.”
When one species is everywhere, it looks like the one holding the place together. Ecologists check by removing species and seeing what falls apart.
The short version
The mistake: The keystone is the most common species, or the biggest one, or the one at the top of the food chain.
What's actually true: A keystone species is one whose removal changes the community far more than its abundance would predict.
- A keystone species has a far bigger effect than its abundance predicts. Ecologists find one by removing a species and measuring the change.
- Sea stars eat mussels. Without them, mussels crowd other species off the rocks, so the number of species falls.
- Barnacles were the dominant species, important because there are so many. Being common, large or a predator doesn't make a species a keystone.
On the exam: Judge a keystone by removal. A big change from a species with little biomass is the sign.