Now that you know a few things about population growth, think again about the sea otter example in the beginning of the previous section. When a sea otter population declines, something has changed the relationship between the birthrate and the death rate, or between the rates of immigration and emigration. For instance, in part of the sea otter's range, the death rate of sea otters is increasing because killer whales are eating the otters. Predation by killer whales creates a situation that reduces the growth of the sea otter population.