Food Webs and Keeping the Balance

A single food chain is a tidy story, but real life is messier. An owl does not eat only mice — it also takes rats and small birds. A mouse does not eat only mielies — it also takes seeds and insects.

When you draw all the food chains of one place on the same page, they cross and overlap. That combined diagram is a food web.

A food web is more useful than a single chain because it shows the ecosystem's alternatives. If the mielies fail, the mouse still has seeds. If the mice become scarce, the owl still has rats. Those spare routes are what keep an ecosystem steady through a bad year.

Worked example — removing one strand.

Suppose farmers poison every owl in a district. Owls ate mice, so with the owls gone the mice have no night hunter. Their numbers climb quickly. More mice eat more stored grain, so the farmers lose more of the crop than the owls ever cost them.

This is why South African farmers are now encouraged to put up owl boxes instead: an ecosystem in balance does the pest control for free.

Other human pressures work the same way — overgrazing strips the grass producers, litter and pollution poison river life, and alien plants like black wattle drink the water that indigenous plants need.