Answer:
Oak trees, grass plants are Producers.
Grasshoppers, deer, mice, and squirrels are Primary consumers, they are eating producers.
Foxes, robins are Secondary consumers, they are eating primary consumers(depending on their nature)
Grizzly bears are Tertiary consumers, they are eating secondary consumers (like snakes)
Mushrooms are decomposer (which decompose, organic material such as remains of dead material)