Which of these animals is an example of an ecosystem engineer?

Ecosystem engineers are species that modify their environment in a significant manner, creating new habitats or modifying existing ones to suit their needs. The beaver is probably the most well-known example of a typical ecosystem engineer who also acts as a keystone species. Beavers cut down trees and build dams in small waterways, backing up water and creating beaver ponds. Beavers manipulate waterways for their own benefit, but these manipulations also provide habitat for many other species. Beaver dams and ponds also play important roles in many abiotic ecosystem processes (e.g., nutrient cycling and siltation). Without beavers to modify existing environments, these important wetlands would not exist and many species would be negatively affected.

Source: The Orianne Society