Richard is an avid gardener who spends a lot of time caring for the plants in his garden. to minimize damage from pests from his garden, richard uses a pesticide spray. at first the spray is very effective and kills off most of the insects that he sees on his vegetable plants. however, after a few years of using the same pesticide he notices that some insects are surviving and continuing to eat his plants. the constant use of pesticides by richard has led to genetic changes in the population over many generations. this is an example of