A pair of beavers were reintroduced to two rivers in 2001. The beaver population was tracked for ten years and the data are displayed below.

a. What is the definition of carrying capacity?

b. Based on the graph, estimate the carrying capacity of River B. Explain how you determined this value.

c. What is one possible reason for why the carrying capacity of River B is higher than that of River A?

d. There was a decline in River B's beaver population in 2009. Provide an example of both a density-dependent and a density-independent factor that could account for this decline.