![]() |
Gray wolves taking down an elk |
Keystone species are almost always predators, and these predators control the spread and population of large numbers of prey species. This is important because if a keystone predator were to disappear it would mean chaos - a great example is gray wolves in Yellowstone National Park. For the 70 years that wolves were absent from the ecosystem, elk flourished...and while the elk increased in numbers they ate a lot of vegetation. Eventually there were no new trees because the elk had eaten the baby sprouts and rivers were eroding since the elk ate from the banks as well. When wolves were reintroduced they began to control elk numbers again, and surprise! New trees began to grow and the landscape became much more lush and shaded.
The effect of keystone predators is that they release a trophic cascade. Since predators impact prey, predators in turn impact their prey's prey - it's like our previous example where wolves indirectly impacted the landscape through their interactions with elk.
Now that we've got the basics, here are some keystone species:
- Sea stars, studied by Dr. Robert Paine who coined the term keystone species, who eat sea urchins, mussels and other shellfish that have no other natural predators - the control of these species allows tide pools to prosper
- Mountain lions partially control number of deer, rabbits and bird species
- Sea otters who control sea urchin numbers preventing urchins from destroying kelp forest habitat
- Prairie dogs whose foraging maintains water in the soil and forces new grass to grow
- Wolves who control populations of elk, rabbits, coyotes
- Elephants who keep savannas from developing into forests because they graze on trees
- and many many more!