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What do starfish and elephants have in common?

keystone species

A starfish is a keystone species


We can’t imagine what a starfish and an elephant might have in common. They all eat different things. Starfish eat meat (hmm, that is interesting) and elephants eat plants. There are only 3 species of elephant, but over 2,000 species of starfish.  They are completely different sizes, with elephants weighing thousands of pounds and starfish weighing only ounces. So how are they alike?

Keystone Species

Well, they are both keystone species. Is this a new species, a keystone? Not exactly.
Think of an arch of stones with a stone at the top, the keystone. Without the keystone, the arch collapses. A keystone species (a plant or animal) acts as the top stone, playing a critical and unique role in maintaining the structure of an ecosystem. This concept was conceived by Robert Paine, an ecologist,  in 1969.

keystone species

The keystone is the top stone in the arch

Back then, he was studying tidal waters inhabited by starfish and mussels off the Pacific coast. The starfish (the only predators of the mussels) kept the mussel population in check. When he removed the starfish from the ecosystem, the mussels took over, crowding out all the other species and the ecosystem collapsed. The starfish (it turns out) were critical to the health of their ecosystem.

In much the same way, the elephants in Africa eat and destroy small trees, making room for grasses for the grazing animals to eat. Without the elephants, Africa would become a woodland and no longer provide grasses for the zebra, wildebeests and other grazing animals.

When a keystone species disappears from an ecosystem, no other species can fill its role. The ecosystem changes, often radically and catastrophically.


So both the starfish and elephant are considered keystone species along with wolves, mountain lions, beavers, the sugar maple, grizzly bears and a host of others. Lions and tigers and bears, oh my!