Copyright © 2007 Dorling Kindersley
All living things have complex relationships with other species and with their environment. The study of these interactions is called ecology. Ecology looks at the FOOD CHAIN that links the eater to the eaten. It also shows how vital chemicals are recycled by NUTRIENT CYCLES.
From a tiny puddle to a vast forest, an ecosystem consists of a living community, its environment, and all their interactions. A community is a group of animals, plants, and microorganisms that live together in the same area, or habitat. Its environment includes sunlight, rainfall, and shelter.
Coral reefs have high biodiversity because they contain large numbers of different species. Deserts have low biodiversity because they have far fewer species. Humans have reduced biodiversity in many ecosystems by harmful activities, such as overfishing.
Ecosystems are continually changing, often very slowly, sometimes very fast. A forest fire, for example, can wipe out an ecosystem without warning. Even so, a new community slowly begins to form. First, short-lived pioneer plants arrive, along with the animals that eat them. These are gradually replaced by larger plants, such as trees, and their associated animals. Eventually, a stable mix of species is established.
In any ecosystem, species eat and are eaten by other species. A food chain is a simple pathway that connects up to six species by what they eat. It describes the route followed by energy and nutrients as they are passed from organism to organism.
The community within an ecosystem can contain thousands of species. Each species may be part of two or more food chains. The interconnected network of food chains in an ecosystem is called a food web. It includes producers that make their own food by photosynthesis, consumers that eat plants or animals, and decomposers that break down dead organisms.
Predators are fewer in number than prey because they are higher up the food chain. In a food chain, an organism passes on only part of the energy it receives from food. With less energy, each level in a food chain supports fewer individuals than the one below it.
Organisms take chemical nutrients, such as carbon, nitrogen, and water, from their surroundings. They then return or recycle them when they respire (breathe) or die.
Certain fungi and bacteria, called decomposers, play a key role. They break down, or decompose, the remains of dead organisms. This releases carbon dioxide back into the air, where it can be reused by plants.
Plants take up nitrogen-containing chemicals, called nitrates, from the soil. Animals obtain nitrogen by eating plants, or animals that eat plants. Bacteria release the nitrogen in dead plant and animal matter, allowing it to be returned to the soil. Nitrogen is an important part of proteins that cells need to survive.