Ecology Notes 4a381c

Compiled by: Ahmed Kalim Niazi Biology/5090

Name: ___________________________ Class/Section: ________/_______ Date: ______________________

3.3 Energy Flow in Ecosystems Food Chains and Food Webs 

Energy flows through an ecosystem in a one - way stream.

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We use ARROWS () to show the transfer of energy: o The arrow always points towards  the MOUTH that is eating! o Like this: Primary Producer  Consumer o Example: Algae is eaten by Flagfish. Flagfish are eaten by Largemouth Bass. This is how we show it: Algae  Flagfish  Largemouth Bass

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FOOD CHAIN: a series of steps in which organisms transfer energy () by eating and being eaten. o In some aquatic food chains (those in the ocean, lakes, etc.), the primary producers are a mixture of floating algae called Phytoplankton. A food chain with Phytoplankton:

Phytoplanktonsmall fishlarge fishwading birdalligator (*note the arrow direction)

o Look at this chain:

 grass



 grasshopper

 

frog



 snake



hawk

o Now add this to the food chain above: 1) Put a CIRCLE around the primary producer. 2) Put a SQUARE around the herbivore. 3) Put a TRIANGLE around the consumer(s). (see 3.2 notes for help)

(Answer: Circle grass, square grasshopper, triangle around all the rest) FOOD WEBS: Most ecosystems are made up of complex feeding relationships and interactions called food webs. 

A food web is a network of all the food chains in an ecosystem.

Food Webs and Disturbance 

Small disturbances to one population can affect all populations in a food web.

EXAMPLE:

Background Facts:

o Zooplankton are a diverse group of small, swimming animals, such as krill, that feeds on algae. o Shrimp, in its third stage of growth, feeds on krill and other zooplankton. Now let's say that Hurricane Katrina wipes out the zooplankton and shrimp population. What would happen? 1) Every organism that feeds on shrimp and/or zooplankton would see a significant drop in their populations (possibly even wiped out!). 2) Algae would have a significant rise in its population because there wouldn't be as many organisms to consume it.

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Decomposers CONVERT/recycle the dead material into usable material (nutrients) for primary producers (plants). Think About It!: What would happen if there were no decomposers? Where do we find decomposers on the food web?

Trophic Levels and Ecological Pyramids 

Each step in a food chain or food web is called a trophic level. o Producers make up the first trophic level. o Consumers make up higher trophic levels. - Each consumer depends on the trophic level below it for energy.

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One way to draw the trophic levels found in an ecosystem is with an Ecological Pyramids. o These pyramids show the relative amount of energy or matter found within each trophic level in a food chain/web.

Pyramids of Energy 

Only a small portion of the energy that es between organisms/trophic levels is actually “stored” in the bodies of the eater. This is because: o The energy is used on life processes such as respiration, growth, movement, metabolism. o Energy is released as heat into the environment - a byproduct of these above mentioned activities.

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About 10% of the energy available within one trophic level is transferred to the next level.

Photosynthesis - Light Energy

Chemosynthesis - Chemical Energy

Heat is released out into the atmosphere at each trophic level. Pyramid of Biomass and Pyramid of Numbers 

Pyramid of Biomass - The total amount of living tissue within a given trophic level is called its BIOMASS. It is demonstrated graphically in a pyramid.

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Pyramid of Numbers - diagram that shows quantities of plants and animals at different trophic levels. The pyramid of biomass is a more useful tool.