Scenario Michigan's Isle Royale Is an Island Located in Lake Superior

Multiple Choice

Scenario
Michigan's Isle Royale is an island located in Lake Superior that is 45 miles long and 9 miles wide. Ecologists estimate that the moose population on the island has been there since approximately the year 1900. The wolf population on the island, on the other hand, has been there only since the winter of 1949. Weather conditions had to be calm and cold enough for the lake to freeze so that the first wolves could make the passage over to the island. When the wolves arrived, they were greeted with a large moose population that had no predators. The moose population was at a dangerously high level but was kept in check by the arrival of the wolves. This "harmonious" pattern continued for at least 20 years.
In 1982, the wolf population suddenly crashed because of a new canine virus believed to have been carried to the island carried on the shoe of a human traveler. While the wolf population size decreased from 50 to 14 individuals in a year, the moose population increased. However, the winter of 1996 was extremely harsh and the moose population experienced a major crash. More than 500 moose died during the winter months, reducing the population to less than 800 animals.
-The harsh winter that led to the death of many moose in 1996 is an example of ________.

A) a density-dependent factor
B) biological control
C) a density-independent factor
D) a trigger for logistic growth