Understanding food webs

Educational value

• A food web is a complex network of food chains illustrating the feeding relationships in an ecosystem. Most animals feed on many other species and in turn are food for many different species. A food chain shows the flow of matter and energy through the ecosystem as each organism feeds on others.
• The source of energy for most food chains is the Sun, the energyfrom which is trapped by producers through photosynthesis. Producers, which are often plants, are consumed by herbivores, and they in turn serve as prey for carnivores. At each stage of a food chain only about 10 per cent of the energy is passed on to be stored as body tissue, so a food web supports successively fewer animals at higher feeding levels.
• The organisms in a food web can be grouped according to their trophic or feeding levels. At the base level are the producers (autotrophs), which in marine ecosystems are phytoplankton and algae. Animals are consumers (heterotrophs), and the organisms that break down wastes and dead tissue are decomposers.
• Humans are the top consumers in their ecosystems and are heavily dependent on the entire network of organisms in the food web. Understanding the food web is important in managing the sustainability of our food resources. In Fiordland, New Zealand, scientific investigations of food webs have resulted in improved management practices such as the setting up of marine parks and reserves.

Year level

5; 6; 7; 8; 9

Topics Food chains Predation Marine habitats Producers (Food chains) Consumers (Food chains) Food webs