They are both adapted to a humid climate.
They benefit each other.
The ants eat part of the acacia tree.
Flowers that can be pollinated by only one species of insect.
Rabbits that invade a new habitat.
Bacteria that suddenly mutate in a lab.
More birds die than are hatched.
Most females lay two eggs instead of three during their nesting season.
Several females begin laying eggs at younger ages than their mothers did.