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 chain is a diagram which depicts the series of organisms which eat each other, starting with a producer (generally a plant) and ending with the apex species. It is useful to think of food chains using the rule of 10% which says that generally each successive species in a food chain receives about 10% of the energy of the preceding species. Food chains are linear, unlike food webs which are more complex.
When studying ecology one of the very important topic is trying to figure out where is energy going in a particular ecosystem. And one of the simplest ways to diagram this out is called a food chain. So it's simple diagram and it shows the path of energy i.e. who is eating who. Now when you study a food chain, there're some terminology that we need to introduce. But one of the concepts that you need to hold in your mind because this is one of the implications of a food chain, is this something that, is this thing that is sometimes called the rule of 10. And the idea of the rule of 10, is that roughly 10% hardly if ever above 20% roughly only 10% of the energy goes from one level to the next. So when you have producers, the things that make the food, they're only going to pass on maybe 10% of the energy they're taking in typically from the sun to the primary consumers which eat the producers.
Then the secondary consumers that eat them, they only get 10% of the energy that these guys have. The tertiary consumers the third level who eat the secondary consumers again you only a passage on a 10% so at every level you get far less energy available. You could have passed the tertiary consumer you could talk about cortinary and pentinary consumers but nobody does really go that far why? Because if you keep dividing by 10 you're running out of the amount of energy, so a lot of times instead of calling it a cortinary consumer they'll just talk about the apex consumer and that's the person at the end of the chain who doesn't get eaten by levels above them. Now that doesn't mean that, that person or that thing will never die, yes they will but then decomposers come along, they just eat anything that's dead and not moving. So what would a food chain look like?
Well here's a food chain for a terrestrial environment so you have some kind of a plant that's the producer, it's eaten by a grasshopper primary consumer then our secondary consumer eats the grasshopper, the snake eats the little jubbly rat thing so he's the tertiary consumer and here is our apex consumer eating the snake. We could call it a cortinary consumer if you come along and you eat the bold eagle naughty. Here we have in the marine environment we have the phytoplankton eaten by the little shrimp thingy which is then the primary consumer which is eaten by the secondary consumer of the samon which is eaten by the tertiary consumer of a pike let's call it that or barracuda. And then along comes the killer whale apex consumer. So these are just showing the flow of energy but that's why we have so many more plants or producers then we have grasshoppers and we have a ton more grasshoppers that we do have rat things.
And we have a lot more rat things, then we have snakes and we have very few of the top apex consumers because they need times 10, times 10, times 10, times 10 of these other organisms below them in the food chain.