The energy flow in this freshwater ecosystem begins with the producers, the grass and algae, being consumed by the primary consumers, the ducks and snails. The ducks and snails are then eaten by the secondary consumers, the mice. The mice are in turn consumed by the tertiary consumer, the fox. This energy flow follows the trophic levels in the food chain, with energy being transferred and passed along from one organism to another. The fox acts as a top predator in this ecosystem, regulating the populations of the lower trophic levels.
