1. Chapter 13: Energy and Nutrients
Section 13-4:
Food Webs

2. Food Chains
A food chain is a simple, straight-line relationship of one organism eating another organism
Not accurate in most ecosystems because there are always more than one type of autotroph, herbivores feed on more than one type of plant, carnivores eat more than one type of prey, etc

3. Food Webs
A food web shows the complex feeding relationships that result from interconnecting food chains.
Even though food webs can be complex, all organisms can be classified as producers, consumers, or decomposers.

4. Simple Food Web

5. More Complex Food Web

6. Food Web Diversity
Generally, energy and nutrients flow from autotrophs to herbivores to carnivores, but there are exceptions:
Coastal Salt Marsh Ecosystem
Marine Ecosystem

7. Coastal Salt Marsh Food Web
AKA estuary
Lots of different types of grasses, but very few animals eat the grasses directly
Herbivores like snails and grasshoppers eat the autotrophs directly, but are not then eaten by consumers

8. Coastal Salt Marsh Food Web
Usually, these insects die and decompose, converting to detritus
Detritus is decaying organic matter and the microorganisms of decay
Each detritus particle is a mini-ecosystem, made of a piece of dead plant or animal matter covered by bacteria

9. Coastal Salt Marsh Food Web
Detritus is then eaten by detritus feeders, such as clams, mussels, plankton, crayfish, shrimp, and crabs
Detritus feeders are then eaten by carnivores
Terrestrial detritus feeders include snails, earthworms, slugs

10. Marine Food Web
In ocean ecosystems, there are long chains of “big fish eats smaller fish,” leading to many trophic levels
Phytoplankton are usually the primary producers
Different parts of the ocean have different feeding relationships because of nutrient availability

11. Marine Food Web
In some spots, nitrogen is in short supply, meaning that the autotrophs are very small
Only small consumers can feed on them
This means fish and other marine life are limited in size.

12. Marine Food Web
Some places are upwelling zones, where currents bring up nitrogen-containing water from deeper in the ocean
Upwelling zones can support larger primary producers, and therefore larger consumers
Tend to be fewer trophic levels between producers and largest consumers