4.2 Ecosystem Structure

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4.2 Ecosystem Structure

• 1. Describe Food Chains and the food web.
• 2. Examine how ecosystem structure is related to
  population changes and the transfer of
  pollutants.
• 3. Predict how introducing a new organism into
  an ecosystem may alter the food chain and affect
  existing populations

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Food Chains and Food Webs

• A series of different organisms that transfer
  food between the trophic levels of an ecosystem
  is called a food chain.
• All food chains begin with producers, which are
  usually plants in land ecosystems.
• The food chain continues to herbivores at the
  next trophic level, followed by one or more
  levels of carnivores. All organisms are consumed
  by decomposers.

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Food Chain
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Food Webs

• Few ecosystems are simple enough to portray as
  single food chains. Most consumers feed at more
  than one trophic level.
• A food web is a network of food chains
  representing the feeding relationship among the
  organisms in an ecosystem.

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Food Web
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Food Web

• A food web includes all the food chains in an
  ecosystem.
• The interactions of the food web link the
  organisms in an ecosystem. Changes in the
  population of one organism can affect many other
  populations.

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Ecological Pyramids

• An ecological pyramid is a diagram that shows the
  relative amounts of energy in different trophic
  levels in an ecosystem.

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4.2 Homework

1. Draw a diagram of a simple food chain containing
   mice, grass, decomposing bacteria, the sun,
   hawk, and snakes.
2. What would happen to the above food chain if a
   cat entered the food chain? Redraw the food
   chain with the cat as a food-web.
3. Do you agree with scientists who think that
   complex food webs are more stable than simple
   ones? Use what you know about food webs to
   answer this question.