The pesticide DDT moves through the food chain as one animal eats another. Bald eagles ingested DDT when they ate fish contaminated with the pesticide. DDT caused the eagles to produce eggs with weak shells, resulting in low birthrates for the birds. The number of bald eagle breeding pairs in the lower 48 states of the United States went from around 100,000 in 1800 to 417 in the early 1960s. In 1972, the use of DDT was banned in the United States. Current estimates put the number of breeding pairs between 14,000 and 15,000. What type of population limit was/is DDT in regard to bald eagles?
a. irregular fluctuation
b. cyclical fluctuation
c. density dependent
d. density independent