A pоpulаtiоn оf islаnd lizаrds contains individuals with either short tails or long tails. After a hurricane, most of the vegetation is destroyed, and birds can more easily spot lizards on exposed rocks. Researchers find that long-tailed lizards survive at much higher rates than short-tailed lizards. Five generations later, the frequency of the long-tail allele has increased significantly in the population. Which explanation best accounts for this evolutionary change?