A3.4.5 Terrestrial Food Web
A ‘Food Web’ therefore attempts to show the wider relationships; organising the complex network of interactions among species.
Source: Champaign Unit 4 Schools © 2008; http://www.champaignschools.org
The relevance of food webs to the effects of pollution is quite simply that the effects of the pollution may impact upon different species to those initially exposed. In the example above, a fox or an owl will eat a mouse, which has eaten plants. If those plants were contaminated, the mouse would ingest the contaminants, which in turn are ingested by the fox or the owl.
It is an unfortunate fact that many birds die due to eating mice that have ingested poison, laid out by man to rid the area of vermin. In the same respect, many birds die through eating slugs that have been poisoned with slug pellets.
Humans are part of a food web as well, albeit near the top! If a person eats meat, which is from an animal that has been affected by a toxic substance, the person will ingest that substance through the meat. An example of this is the consumption of certain fish species, including Yellow Fin Tuna, King Mackerel, Shark and Swordfish. Such species bio-accumulate mercury, which is held in their tissue and then ingested by people when they eat it. Several Governments have issued health warnings advising that children and pregnant women limit their intake of such species.
Further examples of food webs are provided overleaf: