Producer means an organism that can produce it's own food. Plants are prime examples of producers
Primary Consumer means organisms that primarily eat plants and have low energy levels. Squirrels fit into that category. They're almost always herbivores.
Secondary Consumers eat both plants and animals in the Primary Consumer. Crows are technically secondary consumers but I've never seen one eat a squirrel before.
Tertiary Consumers are predators that have the highest energy levels and are at the top of the food chain. Coyotes eat both squirrels and crows.
