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

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

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.

Simple Food Web

More Complex Food Web

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

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

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

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

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

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.

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