This concept is called a food chain.
It works like this:
- Producers: Plants that make their own food through photosynthesis
- Primary consumers: Herbivores that eat producers
- Secondary consumers: Carnivores that eat herbivores
- Tertiary consumers: Larger carnivores that may eat secondary consumers
- Apex predators: Top predators with few or no natural enemies
A bigger fish eating a smaller fish is an example of this pattern, common in many ecosystems where larger predators consume smaller prey.