are substances found in foods that are not in a form directly usable by the body, but that can be converted into an active form once they are absorbed; however vitamins found in foods that are already in the active form, called vitamins, do not undergo conversion.

I Think part of the answer is provitamins and the second answer is  preformed

Explanation:

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.