All organisms need energy to survive. While animals and fungi must obtain this energy from other organisms (living or dead), plants can synthesize energy-rich carbohydrates in the process of photosynthesis. Thus, plants are referred to as "producers" because the virtually all large organisms (other than microbes) depend on plants for food, either directly or indirectly.
to large mammals.
Of course, there are other animals which rely on plant parts other than leaves. Many animals include fruits, seeds, and/or nuts in their diets:
Many animals feed on nectar or pollen at flowers, especially insects.
Many decomposers obtain their nutrition from rotting plant material.
Many insects are primary consumers which depend on plants for their nutrition. Insects themselves are preyed on by secondary consumers such as other invertebrates,
Fish are serve as prey for other fish, amphibians,
birds, and mammals.
Amphibians can be eaten by a diversity of animals including fish, large frogs, snakes, turtles, herons, raccoons. Young turtles are preyed upon by a variety of animals including herons, foxes, and raccoons. Snakes are eaten by larger snakes, hawks, and carnivorous mammals. Birds can be preyed upon by snakes, hawks, falcons, cats, and foxes. Small mammals compose part of the diet of snakes, hawks, and carnivorous mammals. Large mammals can be eaten by coyotes and bears. Many large animals provide nutrition to invertebrate parasites.
A food chain is a sum of predatory relationships. For example, one food
chain could begin with grass (the producer) which is eaten by a grasshopper
(the primary consumer) which is eaten by a garter snake (a secondary consumer)
which is eaten by a red-tailed hawk (a tertiary consumer). A different
food chain could begin with aquatic algae as producers which are eaten
by aquatic insect larvae which are eaten by fish which are eaten by a