🕸️ Webs of life

A keystone animal is one whose job holds a whole habitat together, a bit like the middle stone that keeps an arch from falling. Sea otters keep sea urchins in check so kelp forests can grow, and bees help countless plants make seeds. If a keystone animal disappears, many other living things suffer.

When wolves returned to one big park, they changed far more than the deer they hunt. With fewer deer nibbling everything, young trees grew back, which brought birds and beavers, and the beaver dams even changed how the rivers flowed. One animal set off a chain of effects across the whole land.

Sometimes two very different creatures team up so that both do better, which scientists call symbiosis. A clownfish shelters safely among a sea anemone's stinging arms and, in return, keeps the anemone clean and chases away its enemies. All over nature, partners like these trade favours to survive.

The huge variety of living things is called biodiversity, and it keeps nature strong. Different animals and plants each do a job, cleaning water, spreading seeds, making soil, so when there are many kinds, the whole web can handle trouble. The more variety, the healthier and steadier the living world.