What is the role of the beaver in its ecosystem? a) it is a foundation species and the main source of food for the natural predators of its ecosystem. b) it is a keystone species that modifies its natural environment by damming streams to form wetlands. c) it is a dominant species, as it has the greatest number of individuals among all the mammalian species of its ecosystem. d) it is an endangered species as it has the least number of individuals among all the mammalian species of its ecosystem.