What does the following diagram illustrate?

A food chain because the algae goes to the minnows then the minnows go to the salmon then the salmon goes to the bear :)

the correct answer is:

a population changes in response to a change in the environment.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).