Black guillemot standing on lichen covered rock carrying fish.

Upsetting the food chain

Damage to any part of a food chain can cause problems right along it.

How food chains can be affected

If there are no other routes through the food web, everything at the top of the chain can be in trouble. This is what people used to call 'upsetting the balance of nature.' Sometimes this damage has a natural cause. Often it is the fault of people.

World without plants

Can you imagine a world without plants? Scientists think this happened 65 million years ago, when a huge meteor struck the Earth. Dust from the impact blocked out sunlight, so that all plants died. This left no food for animals, and many – including dinosaurs – soon became extinct. If humans had been around then, we would have died out too. Nothing can survive without energy (as heat and light) from the sun.

Chain of poison

In the 1960s, the peregrine falcon became very rare. The culprit was an insecticide crop spray called DDT. Peregrines do not eat insects or crops, but they eat other birds that do. When pigeons fed on crops that had been sprayed, the poisonous chemical entered their bodies. Each pigeon the peregrine ate poisoned the falcon a bit more. DDT didn’t kill peregrines outright, but it stopped their eggs hatching, leaving many of them unable to breed. Peregrines have become more common since DDT was banned.

Disaster at sea

In 2004, many British seabirds had a disastrous year. On Fair Isle, where thousands of guillemots usually breed, not a single chick fledged. Sandeels – their staple diet – had disappeared. This was due partly to a rise in sea temperature that killed their food, and partly to people catching too many of them in large nets. With sandeels gone, the food chain was broken, leaving seabirds to suffer. 

Alien invasion

When people move plants and animals into a habitat where they don’t belong, it can also cause disaster by wrecking a delicately balanced food web that has taken thousands of years to evolve. American mink are fierce predators, which escaped captivity in fur farms in the UK. They have caused chaos, killing native animals such as water voles and raiding the nests of birds such as ducks and grebes.