The Florida panther's population was reduced to zero in Florida due to overhunting. Panthers were reintroduced to Florida in 1995 and small populations now live in the southern swamplands of the state. Wildlife scientists carefully watch to see how the populations change from year to year. Which of the following events would decrease a population of panthers?
A. Many white-tailed deer move in the panthers' range.
B. Water quality improves in the panthers' habitat.
C. Some panthers emigrate to another area far away.
D. A mother panther gives birth to a litter of two offspring.