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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