Food Chain and Food Webs
Within an actual ecosystem the feeding relations are more complex than simple food chains. This is because tertiary consumers may also feed on primary consumers and secondary consumers. There is also selective feeding among consumers. For example, secondary consumers may not consume all primary consumers and primary consumers may not consume all types of producers. In the food chains containing omnivores such as humans that feed on consumers and producers, then this chain may become more complex. As a result of this complexity, feeding relationships are represented by food webs rather than food chains.
A food web may be defined as a series of interconnecting food chains that shows the feeding patterns amongst organisms in a habitat/ecosystem/community.
Just as food chains, food webs have trophic levels. The lowest level which consists of the producers is the first trophic level. Going up the web, the trophic levels increase as the complexity of the organisms and their feeding patterns also increase.
DIAGRAM OF A TERRESTRIAL FOOD WEB
In the web shown above, there are several food chains present. Because of the commonalities amongst the chains, they can be joined at some point to show the complex feeding patterns of the organisms. There are three trophic levels in the web constructed.
1. The first trophic level consists of the seeds and leaves.
2. The second trophic level comprises of squirrel, iguana, grasshopper and caterpillar.
3. Ocelot, broad-winged hawk and fly catcher are all on the third and final trophic level of the food web.
1. The arrows point towards the organisms that are higher up the food chain. The arrows should be drawn with a ruler, never curved and the arrow-head should not be shaded.
2. Food webs are diagrams so they should be constructed with a pencil. They should also have a title.
3. In this instance, an exception is made concerning crossing lines as this is sometimes unavoidable in food webs.