GED Science Practice Test: Food Webs

While food chains provide a simple way for ecologists to track the flow of energy/food through ecosystems, they are often too simplistic, and don’t represent the reality of the flow of energy and food through the ecosystem.  For example, in our food chain example above, hawks eat snakes.  However, hawks could and do very easily eat frogs.  Rather than a chain, ecologists often represent the complexity of the flow of energy and food through ecosystems with a food web.  A food web shows many or all of the connections between and among communities of organisms.  The following diagram shows the difference between a food chain and a food web.

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Food chains are simple, while food webs are complex.  While food webs may seem too complex to be of much value, ecologists still refer to the various organisms in a food web using terms like consumer and herbivore.  For example, the fox in the food web above is a consumer. One can see this because the fox eats other organisms.  The fox is also a carnivore.  One can see this because the organisms the fox eats do not include plants.  One can identify the producers, or plants, in a food web, because there are no arrows showing these organisms consuming any food; all of the arrows point away from the producers in the food web diagram, above.

Considering communities from a food web perspective allows the ecologist to consider the impacts of population declines or increases on the community of organisms as a whole.  Consider again the food web example from above.  If the chipmunk population declined suddenly, a food source for the fox would be not be as plentiful.  This might mean that the fox would consume more rabbits or mice.  If more mice were consumed, the grasshopper population could flourish.  An increase in the grasshopper population might cause a decline in the growth of grass.

In summary, food webs show the complex food and energy connections within communities. They show all of the possible food sources for a population of organisms.  Many organisms will have more than one food source.  A food web allows an ecologist to show and consider multiple food sources, and the interactions between populations of organisms.

 

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