Secondary consumers are organisms that eat primary consumers for energy. Primary consumers are always herbivores, or organisms that only eat autotrophic plants. However, secondary consumers can either be carnivores or omnivores.
However, with the help of evolution and new technology, humans are now considered the ultimate tertiary consumer. What is unique about secondary consumers is that they can sometimes also be considered primary or tertiary consumers depending on the environment. For example, when squirrels eat nuts and fruits, it is a primary consumer.
Aquatic environments are capable of supporting several types of secondary consumers because of the vast amount of food sources available. Piranhas are an example of aquatic omnivores that eat fish, snails, aquatic plants, and even birds.
Omnivores are the other type of secondary consumer. They eat both plant and animal materials for energy. Bears and skunks are examples of omnivorous secondary consumers that both hunt prey and eat plants. However, some omnivores are simply scavengers.