The classic experiment by Robert T. Paine showed that when the predator Pisaster (starfish) was removed, the mussel population increased rapidly and outcompeted other species, reducing biodiversity.

This demonstrated that:

• Predators can maintain species diversity

• Such predators are called keystone species, as they prevent dominance of a single species

Other options relate to different ecological concepts:

• Prickly pear cactus → Invasive species control

• MacArthur → Resource partitioning

• Connell → Competition (barnacle experiment)