Paul Ehrlich was a :

Stanford ecologist.

The correct answer is Option (1) -Stanford ecologist.

‘Rivet popper hypothesis’ used by Stanford ecologist Paul Ehrlich. "In an airplane (ecosystem) all parts are joined together using thousands of rivets (species). If every passenger travelling in it starts popping a rivet to take home (causing a species to become extinct), it may not affect flight safety (proper functioning of the ecosystem) initially, but as more and more rivets are removed, the plane becomes dangerously weak over a period of time."