Food chains and food webs

Feeling a bit "low" today?... Actually, in the world of nature, you are on top. How so? You'll see... Grass produces its own food by converting carbon-dioxide and water into sugar, with the help of sunshine.

This process is called photosynthesis. Grass is eaten, for example, by a grasshopper. The grasshopper is eaten by a lizard. The lizard is eaten by a snake. The snake is eaten by a bird of prey, like a buzzard.

You can tell from the arrows what is becoming food for whom. This is called a food chain. In a food chain we only see one arrow for every animal that is eating something. But in real life that is not so. There are several species of predator that can eat the same kind of prey.

And often, predators can eat many different kinds of prey. Several animals might be craving a crunchy grasshopper, not just lizards. Like this frog! And maybe a snake might eat the lizard and the frog. By drawing several food chains like this, we can see how they are connected.

We get a web of connections: a food web. Let's back-up a bit to: trees, grass, and other green plants that convert sun energy, water, and carbon-dioxide into energy and carbohydrates. These are at the base of the food web since they produce new energy - new raw material. They are primary producers. Primary means: something that comes first.

In lakes and seas, algae and bacteria are primary producers. Animals that eat plants - rabbits for example - are primary consumers. A predator that eats a herbivore is a secondary consumer, since something in second place is called secondary. And in the same way, a larger predator that eats a smaller predator is called a tertiary consumer. Tertiary comes from the Latin for "third".

So the primary consumer is always a herbivore and the secondary or tertiary consumers are carnivores. The levels in a food chain are called trophic levels. The species that comes last in a food chain - the one that has no others hunting nor eating it, is called a top consumer. This is often a large predator, like a big bird-of-prey, a wolf , or you: a human. Yes!

I'm on top. So, the whole food web is connected. What do you think happens when we humans release environmental toxins - poisons - that end up in the sea? Let's look. Some environmental toxins are fat soluble, and break down very, very slowly.

If there are toxins in a lake or sea, they will also end up here: in the water's primary producers - phytoplankton. When zooplankton eat phytoplankton, these toxins are ingested too - gathering in fat droplets in the zooplankton: in higher concentration. One zooplankter of course, eats not one phytoplankton, but many. And when a fish eats zooplankton the toxin is transferred in yet higher concentration. And so on...

The higher up the food chain the more environmental toxins will be stored in the animal's body. This is called enrichment of toxins or bioaccumulation. I might be on top of a food chain, but I'm a little UNDER the weather...