The term 'Keystone Species' refers to a species that:
- Has the largest population in an ecosystem
- Is the most endangered species
- Has a disproportionately large effect on its environment relative to its abundance
- Is found only in one geographical location
Answer: Has a disproportionately large effect on its environment relative to its abundance
Keystone species, like sea otters or wolves, maintain ecosystem structure; their removal can cause dramatic changes or collapse.