1. What are Food Webs? How are they useful?
Lets look at a food chain again to understand better
The next slide shows a food chain that you’ve seen before

3. Does a food chain give us the whole picture?
Are mayfly nymphs the only thing that eats duckweed?
Is duckweed the only thing that mayfly nymphs eat?
Are frogs the only things that eat mayfly nymphs?
Are herons the only things that eat frogs?
Are frogs the only things that herons eat?
In any community, there are many many food chains and all living things belong to more than one food chain

4. Is there a tool that gives us a better picture of what eats what in a natural community?
Yes!
The food web does!
Let’s watch a short video about the food web of the Florida Everglades. (Far from the Sackville River, but same idea!)
Food Web Video

5. Example Food Webs
Food webs are interconnected food chains from the same community
Like food chains they show the direction of energy transfer in a community
They show interactions between species

6. Let’s make a Food Web from the 4 food chains below
A food web can only be made for organisms that belong to the same community

7. Select the Producers

8. Add the Consumers
Lines point from the source of energy to the consumer
Can you think of any more links that we could add?

9. Energy in Biological Communities
We saw that Energy goes from: Sun  Plants  Herbivores  Carnivores
Plants capture a tiny fraction of the sun’s light energy
Herbivores eat a lot of plants to stay alive and reproduce
Carnivores eat a lot of herbivores to stay alive and reproduce
So there has to be a lot more plant energy than herbivore energy and a lot more herbivore energy than carnivore energy for a community to exist

10. Another Way to Look at it!
Suppose in a small forest, there are 5 foxes.
The mass of each fox is 2 kg.
If each fox must eat ½ kg per day of rabbits, mice & squirrels, in order to stay healthy,
What would be the mass of rabbits, mice and squirrels needed to keep the 5 foxes alive and healthy for 10 days?
How about for a whole year?
What might happen if fox numbers got too high?
What might happen if all the foxes died of some disease?

11. Energy Pyramids
Diagrams that represent how much energy is present in each level of the community of a habitat