Many ladybird beetles live in Pedro's garden. He observed them one summer for a science project. Pedro noticed that all the ladybird beetles had red shells. Some of the beetles had many dark spots, some had only a few dark spots, and one or two beetles had no dark spots at all. Around the same time, Pedro's father replanted the garden using just red flowers. A few years later, Pedro observed the ladybird beetles again. This time he noticed that almost all the ladybird beetles had shells with more red visible. They had few or no dark spots on their shells. Pedro concluded that replanting the garden with red flowers caused a change in the ladybird beetle population. Which best explains Pedro's observations?