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Energy FlowChapter 3-2
Food Chains, Food Webs and Ecological Pyramids
Energy for Life Sunlight is the main energy source for
life on Earth Some organisms have to depend on
other organisms for their energy
Producers Autotrophs – organisms that can
capture sunlight or chemicals and use that energy
Because they make their own food, autotrophs are called producers
Examples of Autotrophs (Producers)
Plants are the main autotrophs on land.
Algae are the main autotrophs in freshwater ecosystems and in the upper layers of the ocean.
Photosynthetic bacteria are important in certain wet ecosystems such as tidal flats and salt marshes.
ConsumersMany organisms cannot harness
energy directly from the physical environment.
Organisms that rely on other organisms for their energy and food supply are called heterotrophs.
Heterotrophs are also called consumers.
Example of Consumers or Heterotrophs
Herbivores eat plants. Carnivores eat animals.Omnivores eat both plants and
animals.Detritivores (Scavengers) feed on
plant and animal remains and other dead matter.
Decomposers, like bacteria and fungi, break down organic matter.
Energy Flow Energy flows through an ecosystem in
one direction– Sun to autotrophs (producers) to
heterotrophs (consumers)
A food chain is a series of steps in which organisms transfer energy by eating and being eaten.
FOOD CHAIN
In some marine food chains, the producers
are microscopic algae and the top carnivore is four steps removed from the producer.
Example Food Chain
What do the arrows show?
ARROWS IN THE FOOD CHAIN
Arrows in the food chain show the direction in which energy is being transferred from one organism to
the next.
EX: Algae fish heron
Number of links in a food chain…
Most food chains have no more than five links.
This is because the amount of energy remaining in the fifth link is only a small portion of what was available at the first link.
A portion of the energy is lost as heat at each link.
It makes sense that most food chains are only 3-4 links long!
Food Web•Ecologists describe a feeding relationship in an ecosystem that forms a network of COMPLEX interactions as a food web.
•A food web links all the food chains in an ecosystem together. • more detailed and include all possible feeding relationships at each trophic level in a community.•A food web is a more realistic model than a food chain
Food Web
This food web shows some of the feeding relationships in a salt-marsh community.
TROPHIC LEVELS Each organism in a food chain
represents a “feeding step” or trophic level.
Producers make up the first trophic level.
Consumers make up the second, third, or higher trophic levels.
Each consumer depends on the trophic level below it for energy.
Ecologists recognize three different types of ecological pyramids:
1. energy pyramids2. biomass pyramids3. pyramids of numbers
Ecological Pyramids
Energy Pyramid:
Shows the relative amount of energy available at each trophic level.
Only part of the energy that is stored in one trophic level is passed on to the next level.
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0.1% Third-level consumers
1% Second-level consumers
10% First-level consumers
Ecological Pyramid
Energy transfer through trophic levels
Transfer of Energy–The more levels that exist between a producer and a top-level consumer in an ecosystem, the less energy that remains from the original amount.–Only about 10 percent of the energy available within one trophic level is transferred to organisms at the next trophic level.
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50 grams of human tissue
grain
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Pyramid of Numbers:Shows the relative number of individual organisms at each trophic level.
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–The main source of energy for life on Earth is A. organic chemical compounds. B. inorganic chemical compounds. C. sunlight. D. producers.
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–Organisms that feed on plant and animal remains and other dead matter are A. detritivores. B. carnivores. C. herbivores. D. autotrophs.
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–How does a food web differ from a food chain? A. A food web contains a single series of energy
transfers. B. A food web links many food chains together. C. A food web has only one trophic level. D. A food web shows how energy passes from
producer to consumer.
–In a biomass pyramid, the base of the pyramid represents the mass of A. heterotrophs. B. primary consumers. C. producers. D. top level carnivores.
–The amount of energy represented in each trophic level of consumers in an energy pyramid is about A. 10% of the level below it. B. 90% of the level below it. C. 10% more than the level below it. D. 90% more than the level below it.
