Natural selection can operate on predator populations as well as on prey. Suppose that over time trees became covered in lichen and the proportion of light moths increased to nearly 100%. What is the most likely consequence for predator populations?

All light moths will be better camouflaged on lichen-covered trees. So, their predators could hardly notice moths on the trees and number of predators will decrease for a while. Predators could then change hunting strategies or seek for other sources of food. Also, let's assume there is variability in eyesight between predators, so those with better eyesight will have greater chance to notice moths and will become more common.