Food chains: following the energy

Almost every living thing on Earth runs on sunlight. Plants, seaweeds and algae are producers: they capture light energy and use it to make sugar by photosynthesis. Everything else is a consumer, getting its energy by eating something else.

Arrows show where the energy goes

In a food chain the arrow points from the food to the feeder. In a stream: algae → mayfly larva → kōaro (a native fish) → kawau (shag). On a rocky shore: tiny algae on the rocks → limpet → tōrea (oystercatcher). In your school garden: dead leaves → slater → spider → riroriro (grey warbler).

Why chains are short

At each step most of the energy is used for moving, growing and keeping warm, or escapes as heat. Only about a tenth passes on to the next feeder. That is why a field has far more grass than rabbits, and far more rabbits than hawks. Top predators are always rare.

The clean-up crew

Decomposers are the living things that feed on dead plants and animals. Fungi, bacteria, worms, slaters and springtails break them down and return nutrients to the soil or water, where producers can use them again. Energy flows through an ecosystem in one direction, but nutrients go round and round. Without decomposers, dead leaves would pile up forever and plants would run out of food.

Webs, not chains

Real ecosystems are food webs: most animals eat several things and are eaten by several others. If one link changes, the effect ripples. When mud clouds a stream, algae get less light, mayfly larvae get less food, and fish get fewer mayflies.

People are part of the web

Clearing bush, draining wetlands, adding fertiliser, bringing in predators, fishing, planting trees and composting all change food webs, for better or worse. Your investigation is about finding out which changes matter most in your place.