Food webs
The source of energy that supplies all the ecosystems of the biosphere is the Sun. For the biosphere to survive, energy and nutrients must flow through its ecosystems, and food webs are the natural feeding relationships through which they flow.
Food web
The interlinked feeding relationships between living things are called food webs.
In the biosphere, food webs usually form as a net-like relationship between the trophic levels of many food chains. In them, animals depend on several kinds of food. That is important for their survival, and it prevents biological build-up.
Figure to be added
Assignment 15.3
Build a food web you could see in a pond ecosystem.
For example: algae and water plants → water snails, tadpoles and small insects → small fish and frogs → water snakes, kingfishers and herons; the small fish are also eaten directly by the kingfisher and the heron, and dragonfly larvae eat tadpoles.
Why a web is safer than a chain
If the hawk in figure 15.7 ate only rabbits, a disease that wiped out the rabbits would starve the hawks too. Because it can also eat snakes and roadrunners, it survives the loss and turns to other prey, which in turn lets the rabbits recover. A web with many links spreads the risk; a community with few links is fragile. This is one reason why losing species matters: each lost species removes links from the web, and the whole community becomes easier to upset.
Many feeding links
A food web is the network of feeding relationships formed by many food chains; animals that eat several foods survive changes better.