Diagram 3
6. Since 1972, Dr. Jim Estes had been studying a food chain of kelp → urchins → sea otters. He tracked sea otter populations off the coasts of four different Alaskan Islands. In the early 1990s orcas began eating the sea otters.

a. Who is the keystone species in this ecosystem? Explain.

b. Use the data provided, food web, and your own inferences to
describe the trophic cascade taking place in this ecosystem (give at least 3 specific impacts).
Otter No. (% max. count).

c. What resource will kelp crab and sea urchins compete over? Is this
an example of interspecific competition or intraspecific competition?

d. By which method, quadrant or mark recapture, do you believe
researchers would have used to estimate the sea otter abundance?
Explain.