05 April 2014

# 140 Food web

Food web is a network of interconnected food chains showing the energy flow through part of an ecosystem.

These are a more accurate way of showing feeding relationships than food chains, because most animals have more than one food source. For example, in the food webs in figure below, the leopard feeds on baboons and impala.

The leopard can be placed at 2 different trophic levels:
  • secondary consumer (feeding on imlala) 
  • quaternary or fourth level consumer (feeding on baboons).

Another example of food web.

Food webs are easily unbalanced, especially if one population of organisms in the web dies or disappears. This may happen for a number of reasons, including: 
  • over–predation or hunting
  • disease
  • pollution
  • use of pesticides
  • lack of food (or other resources)
  • emigration.
For example, in the food web here, if all the baboons were killed by hunters the leopard would have only impala to eat. So the impala population would decrease. The scorpion population may increase because of less predation by baboons, but if there are more scorpions they will eat more locusts, reducing the locust population, and so on.

Try this 

Figure below shows a food web:

1. Select appropriate organisms form the food web to complete each column in the table below.                                                                           [4 marks]

Organism 1

Organism 2

2. Ladybirds eat aphids. A very large number of ladybirds arrive in the habita where these organisms live. Predict some of the possible effects this could have on the organisms in the above food web.                                    [6 marks]



b) 6 suggestion such as:
  • decrease in aphids because ladybirds eat aphids
  • increase in ivy because there will be fewer aphids feeding
  • decrease in wrens because there are fewer aphids to eat
  • decrease in caterpillars because the wrens now have only caterpillars for food
  • increase in oak trees because there will be fewer aphids feeding
  • increase in hogweed because there will be fewer aphids feeding
  • increase in goldfinches because there is more hogweed to eat.

There are other possible suggestions. 

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