How does the environment inﬂuence natural selection?
Natural selections acts on the phenotype and the phenotype is the the result of the interaction between genotype and environment
In a population, the natural selection will favour the individuals with the higher fitness (In other words : the ones which have the best chances to survive and reproduce) in a given environment.
Natural selection take effect on the phenotypic level. Also, remember that the phenotype is the result of the interaction between genotype and environment.
It means that, for different environment, one gene can give different trait values at the phenotypic level.
This picture illustrate the fact that, for different environments, a genotype can give different phenotypes. For example, in the environment 2, the genotype of our two individuals will give almost the same phenotype. Here, since the phenotypes are not different, there will be no natural selection between the two individuals.
However, in environment 1, the two genotypes give quite different phenotypes. In this case, natural selection can occur and select the one with the higher fitness.