Answer:
If an environment rapidly changes and an organism cannot adapt it will mostly die out. For example, some birds have long, thin beaks that let them reach insects inside trees. If these insects were to disappear for some reason and seeds became the main food source then the birds with long, thin beaks would not be able to eat. Other birds with different adaptations, like short, strong beaks, would be properly adapted to this new environment. So, this second species would replace the first species.
