Which organism might be considered a keystone species in a food web? Explain.
a) Sea otter - Sea otters help control the population of sea urchins, preventing overgrazing of kelp forests.
b) Blue whale - Blue whales feed on krill, which helps regulate krill populations and maintain balance in marine ecosystems.
c) Bald eagle - Bald eagles are apex predators that play a role in controlling populations of fish and small mammals.
d) Monarch butterfly - Monarch butterflies contribute to pollination and are essential for the health of many plant species, but they are not typically considered keystone species.