One day two rabbits are hoping around, having fun with each other. One of the rabbits is red and one is tan. Rosita, the red one, stands out a lot against the tan landscape and Todo, the tan one, blends in with the tan landscape.
Rosita and Tom reproduce. Rosita and Tom produce a lot of offspring, more then the ecosystem can support.
The offspring are half red and half tan. This creates variation within this rabbit species.
An eagle moves in because of the abundant food. He can only see the red rabbits so he swoops down and feeds on them. The tan rabbits survive while the red rabbits get eaten by the eagle because the tan rabbits are camouflaged against the tan landscape. This means the tan rabbits are the best adapted for this ecosystem.
The tan rabbits are the best adapted individuals to this ecosystem because they have camouflage. The eagle will continue to feed on red rabbits but not the tan ones because he can't find them so when they reproduce a large majority of the population will be tan because there are more tan rabbits left. The tan rabbits survive and pass down their characteristics.
These rabbits will continue to adapt because the inherited tan characteristic increases the chance that the rabbits will survive.