Food Chains and Food Webs

- all organisms need a source of energy (or food)

- organisms can be put in categories depending on how they get energy (or food)

1.       Producers

          a.       plants

          b.       use photosynthesis to use solar energy to make their own food

          c.       also called autotrophs

          d.       produce food for all other organisms in the ecosystem

2.       Consumers

          a.       animals

          b.       also called heterotrophs

          c.       must eat other organisms because they cannot make their own food

          d.       4 different kinds of heterotrophs

                    i.        carnivores - eat other consumers. Two kinds of carnivores are predators or scavengers. Predators eat live prey, scavengers eat something which is already dead.

                    ii.       herbivores - eat producers

                    iii.      omnivores - eat both producers and consumers

                    iv.      decomposers - eat dead organisms or waste from organisms. Decomposers are important because they are like recyclers which return nutrients to the ecosystem.

Food Chains

Food chain - a diagram that shows the flow of energy (or food) from plants to consumers

Building a food chain

1.       1^st step is always a producer because they can produce food for all others

2.       2^nd step is always a herbivore (or omnivore) because they must eat a producer. This organism is called a primary consumer.

3.       3^rd step is always a carnivore (or omnivore) because they must eat a consumer. This organism is called a secondary consumer.

4.       The last organism in the chain is called the top carnivore. It is not prey to any other organism

5.       Each level of the food chain is called a trophic level

Food Webs

- in nature, feeding relationships are much more complex than simple chains

- organisms usually have several choices of what they will eat

- food web show these choices

- the more complex the food web the more stable the ecosystem. This is because if one organism is removed, others still have other options for food.

Organisms depend on one another in ways other than feeding

Symbiosis - long term interaction between organisms. There are 3 types:

1. parasitism - one organism benefits but the other is harmed. The parasite gets nutrition from the host.

2. mutualism - both organisms benefit

3. commensalism - one organism benefits while the other is neither helped nor harmed