Food Webs

Food webs show how energy moves through many different communities (groups of different species) in the ecosystem.

Arrows point from the source of the energy to the organism that is getting the energy - from the food to the eater.
Usually, producers are at the bottom, and arrows generally point up towards higher consumers.
Food webs allow you to predict effects of certain populations getting larger or smaller.

Flow of Energy

Energy flows one way through a community, it doesn't cycle, and generally, arrows should point upward.

Producers should be at the bottom
Herbivores should be on the next level, with carnivores above them.
Tertiary consumers should be at the top
When asked to label a trophic level, go with the highest level possible based on the information given.
- The hawk eats squirrels (herbivore), and snakes (carnivore), so it is considered a tertiary consumer.

When a population increases or decreases, it can affect other species in the food web.

If a prey species is reduced, predators will either decrease or rely more heavily on another food source.
- A late spring freeze could reduce the caterpillars. If so, the blue jays would need to eat more grasshoppers or they might starve.
If a predator is removed, it's prey can overpopulate and decrease the producers.
- As humans have overhunted wolves, the deer have increased greatly. In some drier parts of the country, this has reduced the available grass.
- A Keystone Species is one that, if removed, causes the entire ecosystem to change or collapse.
If producers are removed, the entire food web could crash because there is less available energy.
- If a wildfire kills the grass down to the roots, no animals will be able to live in that area until the grass grows back.