What type of selection occurs when an environmental condition, for example food source characteristics, causes selection toward one extreme of a trait's range of variation?

Directional

Explanation:

In population genetics, for natural selection to occur there must be a variation that will favor the survival of an individual.

Directional selection is a form of natural selection that occurs in the extreme end when an environment condition such as food favors one phenotype over the other.

This will make the allele Frequencies to shift towards the direction of the superior phenotype.