Wetlands Web

Food Chains and Food Webs

by Karen Marks

Oh what a tangled web we weave, when first we start to feed...
 
A simple food chain begins with the sun. Plants absorb sunlight and use this energy in the process of photosynthesis to create simple organic compounds otherwise known as carbohydrates (sugar). This form of “food” provides energy to the plant itself and to animals that eat the plant, creating a flow of energy through different stages referred to as trophic levels. Since plants produce their own food they form the base trophic level, and are named the primary producers. Animals in the next trophic level that eat the plants (herbivores) are described as primary consumers. In the next trophic level, predators that feed on the herbivores are identified as secondary consumers. These animals then become prey for the top predator in the food chain level called tertiary consumers. As one organism consumes another, the availability of energy across the trophic levels gradually dwindles from the beginning to the end of the food chain.

Like a spider’s web – food webs can become very complex. (See animation of a coastal marsh food web.)Food webs are made up of a network of food chains found within an ecosystem.  For example, many species of plants and animals form multiple links within a food web of a coastal marsh.  This diversity includes primary producers (plants and algae), decomposers (bacteria and fungi), and primary, secondary and tertiary consumers (amphibians, birds, fish, invertebrates, mammals, and reptiles).  Decomposers such as bacteria play a dual role, in that it promotes plant decay which provides food for the detritus feeders and releases nutrients back into the system for the plants to absorb.

While a food chain can be viewed as a simple one-way street for energy flow, from one level to the next, food webs become a maze of intricately woven strands of energy pathways flowing through the multiple predator – prey relationships for a diversity of species located in all of the trophic levels.

Primary Consumers:
Primary consumers feed on plants and assimilate the energy produced by the plants.  The diet of these herbivores may change with the seasonal availability of the various plants parts, such as the seeds, fruit, nectar, leaves, or roots. Primary consumers include many different types of wildlife and may range in size from a small insect such as a caterpillar or millipede, to large mammals such as the White-tailed deer.  Other examples of primary consumers include the Texas Tortoise which prefers the fruit of prickly pear cacti, and some field mice.  In a food chain, the primary consumers gain the most energy and provide the link in the food chain between the primary producers (plants) and the secondary consumers who do not eat plants.

Secondary Consumers:
Secondary consumers are the next link in the food chain and fee on primary consumers. In some cases, some secondary consumers may also feed on plants. Like primary consumers, secondary feeders include many different types of wildlife. Ladybugs feed on aphids. Ornate Box Turtles feed on caterpillars, grasshoppers and beetles.  The Common Raccoon has a fondness for crayfish.  The Eastern Screech Owl feeds on large insects and small rodents. The energy available to the secondary consumer is less than that of the primary consumer.

Tertiary Consumers:
Tertiary consumers are considered to be the top of the food chain and typically do not have any natural predators. The diets of tertiary consumers may include animals from both the primary and secondary trophic levels. Like secondary consumers, their diet may also include some plants.  Examples of tertiary consumers include Hawks, Alligators and Coyotes. Hawks feed on small mammals, lizards and snakes. Alligators feed on fish, birds, small mammals and turtles. Coyotes are known to eat anything. However, the natural prey of coyotes in the rural setting includes rabbits, rodents, and carrion. These tertiary consumers gain the least amount of energy in the food chain.