GED Science: Food Chains

Within an ecosystem, there are a variety of plants and animals that live together. Remember that plants and animals are the biotic, or living, components of the forest ecosystem. Within an ecosystem, we can talk about a population of fir trees, or we can talk about a population of beetles.  Additionally, we can talk about the bigger community of fir trees, beetles, birds, and foxes.

When considering the community of organisms that live within an ecosystem, one thing ecologists study is how organisms meet their energy requirements, or how organisms get or make food. On a simple level, one can follow the flow of food from one organism to another organism to another.  This type of tracking of food/energy is called a food chain.  Below is a sample food chain:


In this example, you see that hawks eat snakes, snakes eat frogs, frogs eat grasshoppers, and grasshoppers eat grass.  All food chains have a number of things in common, regardless what community of organisms you are studying, or in what ecosystem those communities are found.   For example, at the start of every food chain is a plant of some type.  In our ecosystem above, the plant is grass.  In a food chain, plants are called producers, because they produce their own food from the sun.  The term autotroph refers to organisms that make their own food. You will often hear ecologists and others refer to producers as the “base” of the food chain.  The sun is an important part of any food chain.  Notice that the sun is an abiotic component of a food chain.

The rest of the animals in the food chain are termed consumers, because they consume other organisms (plant or animal) for food.  The term heterotroph refers to organisms that do not make their own food, but rather find or ingest other sources of food. So, in our example above, grasshoppers, frogs, snakes, and hawks are all consumers.  However, it is easy to see that it is not very descriptive or precise to simply refer to them all as consumers.  Thus, ecologists differentiate the consumers by where they are in the food chain.  Grasshoppers are primary or first-order consumers, frogs are secondary or second-order consumers, snakes are tertiary or third-order consumers, and hawks are fourth-order or quaternary consumers.  Sometimes, the organisms at the end, or “top” of the food chain are called apex predators.

Alternatively, ecologists can classify consumers by what type of organism they eat. Consumers that eat plant material are called herbivores (notice that all first-order consumers are herbivores).  Consumers that eat other animals are called carnivores.  Consumers that eat both plants and animals are called omnivores.  Humans are omnivores, because we eat things like lettuce, carrots and tomatoes; as well as fish, chicken, and cows.

Additionally, all food chains have organisms that break down, decompose, or consume dead organisms.  Organisms such as bacteria and fungus are called decomposers, because they break down, or decompose, dead plant or animal material.  Because decomposers feed on detritus, or dead animals or animal materials, decomposers are often called detritivores. The decomposers are not pictured in the diagram above, but they act at every level.  Decomposers break down plant and animal material and return it to the soil, where it can serve as nutrients for further plants.  Without decomposers, dead plant and animal material would build up rapidly.   Another type of organism often found in food chains are scavengers, which eat dead animals.  Vultures and raccoons are examples of scavengers. Scavengers are a type of detritivore that specializes in dead animals.

While it may seem like there are a number of terms that overlap here, there are basically two categories of terms used to describe organisms in food chains. One set of terms refer to the source of food, and another set of terms refer to the category of food eaten. It might help to consider them all in terms of the example food chain pictured above:


To summarize, food chains look at how communities of organisms (such as grasshoppers, grass, and frogs) interact with each other in terms of food.  In food chains, you can examine how individual populations of organisms (such as the grasshopper population) obtain food.  Populations of organisms in food chains can be described in terms of the source of their food, the type of food consumed, and the way in which food is obtained.


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