A closer look at the food web
Monacia Williams, Contributor

How are you all this week? Did you take up the challenge I left you with last week? You did? Good for you! If you continue in this manner, you are on your way to achieving a grade one.

In our cherry tree, there were many food chains in operation at the same time. All of them shared the same producer and some of the secondary consumers fed on the same primary consumers. This means that we cannot look at food chains in isolation because the feeding relationships of organisms within an ecosystem are complex. One organism may feed on more than one type of organism and may, in turn, be eaten by more than one type. If we were to link all of these food chains together, we would get a food web.

Feeding relationships

A food web shows the feeding (energy) relationships between all the organisms in an ecosystem. Below, we use the organisms from our cherry tree to create an example of a simple food web.

Figure 1

• All the arrows point to the organism that is feeding; that is, away from the organism that is being eaten.
• The organism at the base of the web on the first line is the plant. This line represents trophic level number one and this organism is the producer.
• All the organisms that feed on the producer are placed in a line above the producer. This line represents trophic level number two and these organisms are the herbivores or primary consumers.
• All the organisms that feed on the primary consumers are placed in a line above the primary consumers. This line represents trophic level number three, and these organisms are the secondary consumers.
• All the organisms feeding on the secondary consumers are placed in a line above the secondary consumers. This line represents trophic level number four, and these organisms are the tertiary consumers.
• Some organisms can be classified as both secondary and tertiary.

All the examples so far are of organisms living on land. Do you remember the name given to these organisms? If you said terrestrial, you are perfectly correct! Remember, though, that aquatic environments are also filled with living organisms and they also share similar feeding relationships. Aquatic producers include algae, pond weed and microscopic plants called phytoplankton, while consumers include insect larvae, such as those of mosquitoes and dragonflies, snails, tadpoles, fish and water birds. The fish can either be a secondary or tertiary consumer, while the bird is the top consumer.

Again, I close this week's lesson with a challenge! Use these organisms to construct some aquatic food chains, then try to organise them into a food web! Have fun. See you next week!

These Ascot High School students catch up on biology at the Portmore Mall in St Catherine. - Anthony Minott/Freelance Photographer

Monacia Williams teaches at Glenmuir High School.