Biologists Recently Determined That the Lion Population in the Serengeti

Biologists recently determined that the lion population in the Serengeti was growing exponentially. To protect the zebra and hyena populations, two of the lion's common prey animals, biologists captured 100 lions and moved them to a neighboring region. However, in the five years since the lions' removal, the zebra population has declined dramatically.
Which one of the following, if true, would most help explain the phenomenon described above?

A) Zebras and hyenas are both much smaller than lions, making them easy prey.
B) Zebra and hyena populations are constantly in flux.
C) Both zebra and hyena populations have been impacted by a recent drought in the Serengeti.
D) While lions prey on zebras and hyenas, hyenas also prey on zebras.
E) While lions prey on zebras and hyenas, zebras also prey on hyenas.