Food Web
The sources of energy in this food web are grasses and plants. The animals tat eat the plants and grasses are hunted down by bigger animals who then eat them. That food energy gets passed from one animal to another after it has been eaten. but the smaller animal gives less energy to the bigger animal. as the energy goes up the food chain, they receive less and less energy, so in that case the bigger animal would have to eat more food to receive more energy.
If an invasive animal were to come into another land and eats a lot of the other animals, none of the native animals would know what it is and wouldn't eat it. This is a way some animals could go extinct. For example, if a python were to come into Indiana, the python would eat many different animals. None of the others would eat it, so the python would be at the top of the food chain. The python would also reproduce so all of those pythons would feed off of the animals and they would go extinct.