Question

Individuals in a species of moth vary in wing color from white to black, but all individuals prefer to land on the white bark of birch trees. White wing color and the behav- ioral preference for landing on white birch bark are adapta- tions, because the wing color of the moth matches the white color of the birch bark and predators have trouble finding white-winged moths on these trees. As a result, white-winged individuals experience lower predation than dark-winged individuals when landing on birch bark. Now consider a population of these moths that live near a power plant that burns coal and emits black soot that coats the bark of birch trees, turning them black. These moths still prefer to land on birch trees, but now white-winged indi- viduals suffer very high predation because the color of their wings contrasts with that of the soot-covered black bark. Dark-winged moths now experience very low preda- tion because they are difficult to see on the dark bark. Is the behavior of landing on birch trees still a behavioral adapta- tion in this population of moths? How would you test this ?

Answer 1

Yes the behavior of landing on birch trees is a behavioral adaptation in this population of moths but this is only correct for the black moths. This is because due to darkening of the birch bark, black moths tends to avoid predation at a much faster pace as compare to white moths which are easily spotted. Now this increased fitness of black moths due to the industrilization of the area has caused them to avoid predation and increase themselves in terms of their population.This change in environment is beneficial for black moths while this has caused low fitness level in white moths. So in this changed environment, the conditions that are adapted by black moths is their preference of landing on black birch barks. So they established a adaptation as per the change in the environment. To test this we simply change the colour of a birch bark in such a area and see the number of black moths which prefer to hide on this artificial white birch bark. We will see that due to their natural adaptation, black moths donot prefer to sit on such barks. So they have acquired this in their behavioral adaptation.

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