FOOD CHAINS

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.

plants and riverbed
Some animals feed directly on the leaves of plants. Herbivores can range is size from small insects…

caterpillarsgrasshopper

to large mammals.

deer

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:

turtlecardinal

bear

Many animals feed on nectar or pollen at flowers, especially insects.

fly on flowerbee

butterflyhummingbird

Many decomposers obtain their nutrition from rotting plant material.

mushroomsmushrooms

Many insects are primary consumers which depend on plants for their nutrition. Insects themselves are preyed on by secondary consumers such as other invertebrates,

dragonflyspider

fish,

fish

amphibians,

frognewt

reptiles,

snake

birds,

woodpeckerwarbler

and mammals.

Fish are serve as prey for other fish, amphibians,

frog

reptiles,

turtlesnake

birds, and mammals.

 

EAGLEheron

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.

mosquito

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 river otter.
Food chains are important in our understanding of the environment. Any change which affects one organism can indirectly affect the consumers which feed on it and the higher level consumers which feed on these animals and so on. Because pesticides are not broken down by the body, they tend to accumulate at higher and higher concentrations in animals which are higher and higher in the food chain. Thus, a pesticide which is present in low concentrations in aquatic insects can accumulate to a much higher concentration in fish-eating birds or humans which feed on fish.