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Food Web

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

A food web is a diagram that shows all the pathways of energy flow in a community. The food web is similar to a food chain in that it depicts organisms which eat each other. However, a food web is more complex as it shows how herbivores, carnivores, omnivores, decomposers and detritivores interact with one another.

When studying a particular ecosystem ecologists like to learn who is eating who, where are all the connections between the different organisms? How are they passing on the energy and to do that, you need to go beyond the simple food chain into what's know as a food web. And that's the diagram that shows all the pathways of energy flow within a particular community.

Now you'll have these terms that are used to describe the various organisms in that community. There's the producers, they're the ones that are producing or making the food. Typically there're plants or algae, they're the consumers which are not making their own food instead they consumer other organisms. This can be classified as herbivores which eat producers, carnivores the word carni means meat so they're eating the other consumers. Herbi just as a side not means plants and that's why they're called herbivores because they're eating the plants or producers. Omni is a root word that means all, so the omnivores eat all other things. Anything that they see they can eat it, so it's like you looking at some broccoli you'll eat it, pig if you like eating pork whatever you want to eat you can eat it.

Decomposers sometimes are called detritivores because they eat detrities, they don't hunt down and kill other things, they don't make their own food instead they're the clean up curr they're the ones that are eating the dead organisms or sometimes the partially digested organisms. What they do by eating the dead decaying organic matter is that they recycle the nutrients that are locked up in those dead bodies. For example, I hope never to be mould by a bear so nothing is going to eat me. Instead when I die I'll eventually be decomposed by various fungi or bacteria that'll slowly return the calcium and phosphorus and all the other inorganic minerals that are in my body back into the environment.

Let's take a look at the food web. Now down the bottom are producers are the phytoplanktons and the vegetation that's either in or around the water. Now you can see they're being eaten by these herbivores the primary consumers and then those are being eaten by the secondary consumers. But you're seeing that there are some weirdnesses going on here unlike a simple food chain where it's 1, 2, 3 here we see the zooplankton are in the phytoplankton but this small fish is eating both the phytoplankton and the zooplankton. So is this a primary or a secondary consumer? It's kind of both it depends on what level you're talking about. That's why it's important to understand that those terms I was talking about are general terms. They're not always used in every specific example but they're useful in discussing comparing 2 different groups between 2 different situations. So you can see here there's many flows of energy so one organism usually does not depend entirely on one other organism as its food supply.

In a more diverse food web is encouraging to ecologists because it helps them see a very healthy environment. If you have a food web that doesn't have a lot of branches that means that food web is more vulnerable. If one organism in the chain dies then many other things may die too. So that's why it's so important to understand the food web of a particular community in the environment.