Living in the wild is pretty dangerous!
You spend all the time trying to find your dinner and avoid ending up as someone else's.
We can look at who eats whom in the environment by setting up food chains and food webs. They help us by breaking up the environment into understandable bits.
With a food chain you always start off with a plant as they produce all the energy in the environment from photosynthesis. A plant is therefore called a producer.
Herbivores are animals that eat plants and they are placed next in the food chain. They consume the plants and so are also the primary consumers.
To show that the herbivore eats the plant in our chain we use an arrow.
The example food chain below shows this:
The direction of the arrow is very important. It shows who is eaten by who.
So in our example the pea plant is eaten by aphids, which are in turn eaten by the ladybirds, and so on.
If the aphids are the primary consumers here, or the herbivores, the ladybird is the secondary consumer. Then the robin is the next (tertiary) consumer, and so on.
So in our example the ladybird, robin and hawk are all examples of this.
The robin does not just eat other animals but will sometimes also eat fruit and nuts. Therefore you could actually call it an omnivore.
The hawk is the top carnivore as nothing else will eat it.
Our example was very simple. Usually in natural ecosystems they are more complex, this is because one predatory species will usually eat more than one prey species.
What would happen if you were an animal that only ate one animal or plant?
If that food source ran out, you would starve to death. Not a good idea.
Another good idea for eating up your greens!
Animals tend to eat food from a variety of sources, different plants and animals.
Therefore our food chain is not very accurate, it does not cover all the connections.
In order to obtain a more accurate idea of what is going on we need to construct a food "web":
The food web attempts to show which organisms eat any other animal. They can get pretty complicated but are still as easy to read as a food chain. Just remember the arrows.
Now think about what happens if one animal species gets wiped out.
What do the robins do if all the ladybirds disappear?
They just start eating more caterpillars and slugs.
The top carnivore, the hawk, might still be in trouble if all the robins got eaten by cats.