Ecology

A food chain is a straight line: producers get energy from the sun, herbivores eat producers, and predators eat herbivores. At each step, most of the energy an organism takes in gets used for moving, growing, and staying warm, or is simply lost as heat. Only about ten percent gets stored in new body tissue that the next level up can actually eat. That is why energy shrinks fast as you climb the chain, and why top predators are always rare compared to the plants far below them.

A food web is what a real ecosystem actually looks like: many chains overlapping, with arrows showing who eats whom. Because most species have more than one food source and more than one predator, a food web has backup paths built in. If one species disappears, others sharing its arrows can shift to alternative prey, so the web usually absorbs the loss. A food chain has no such backup. Cut one arrow and the whole line breaks, which is why chains are a simplification and webs are the more realistic model.

This connects to population and predator-prey questions elsewhere in the unit. Removing a top predator does not just affect the species right below it. The herbivore population it used to control grows unchecked, overgrazes the plants two levels down, and the damage ripples through the whole system. Reading a food web means tracing those ripples: find the arrows connected to the removed species, then ask what each neighbor does next.