Food Webs

Review

• Food chains represent flows of matter and energy

• They are always pyramid shaped

Energy Flow in Ecosystems

• Three things can happen to the energy taken in by the organisms in a trophic level:– It can be passed on to the next trophic level in the food

chain when the organism is eaten. – It can become stored in detritus. This energy is passed

on to decomposers when the detritus decays. – It can be converted to heat energy by inefficient

chemical reactions, radiated by warm bodies, or in friction due to movement. The heat energy is lost to the surroundings, and cannot be regained by living organisms.

Grazer Food Chains .

• Begins with plants

Grazer Food Chains

Detritus Food Chain .

• Begins with dead material or waste

Detritus Food Web• numbers are very high• organisms are small• don’t move a lot• consume organic wastes• releasing a great deal of

energy mostly as heat • converting it back into its

inorganic nutrient form

algae, bacteria, slime molds, fungi, protozoa, insects, mites, crustaceans, centipedes, mollusks

Detritus Food Web

• By far the most important food web in a forest.– Not much is removed

from the forest, nutrients are recycled.

Detritus Food Web• Detritus food chains are connected to a

grazing food chain when consumers of a grazing food chain feed on the decomposers of the detrital food chain

• In some ecosystems, less than 1% of energy may move through the grazing food web while over 99% moves through the detritus food web

Food Webs

Pond Food Web

Land Food Web

Marine Food Web

Pond Food Web