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13.3 Energy in Ecosystems
KEY CONCEPT Life in an ecosystem requires a source of energy.
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13.3 Energy in Ecosystems
Producers provide energy for other organisms in an ecosystem.
• Producers get their energy from non-living resources. • Producers are also called autotrophs because they make
their own food.
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13.3 Energy in Ecosystems
Producers provide energy for other organisms in an ecosystem.
• Consumers are organisms that get their energy by eating other living or once-living resources.
• Consumers are also called heterotrophs because they feed off of different things.
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13.3 Energy in Ecosystems
Almost all producers obtain energy from sunlight.
• Photosynthesis in most producers uses sunlight as an energy source.
• Chemosynthesis in prokaryote producers uses chemicals as an energy source.
carbon dioxide + water + hydrogen sulfide + oxygen sugar + sulfuric acid
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13.4 Food Chains And Food Webs
KEY CONCEPT Food chains and food webs model the flow of energy in an ecosystem.
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13.4 Food Chains And Food Webs
A food chain is a model that shows a sequence of feeding relationships.
• A food chain links species by their feeding relationships. • A food chain follows the connection between one producer
and a single chain of consumers within an ecosystem.
DESERT COTTONTAIL GRAMA GRASS HARRIS’S HAWK
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13.4 Food Chains And Food Webs
• Consumers are not all alike. – Herbivores eat only plants. – Carnivores eat only animals. – Omnivores eat both plants and animals. – Detritivores eat dead organic matter. – Decomposers are detritivores that break down organic
matter into simpler compounds.
carnivore decomposer
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13.4 Food Chains And Food Webs
• Specialists are consumers that primarily eat one specific organism or a very small number of organisms.
• Generalists are consumers that have a varying diet.
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13.4 Food Chains And Food Webs
• Trophic levels are the nourishment levels in a food chain. – Primary consumers are herbivores that eat producers. – Secondary consumers are carnivores that eat
herbivores. – Tertiary consumers are carnivores that eat secondary
consumers. – Omnivores, such as humans that eat both plants and
animals, may be listed at different trophic levels in different food chains.
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13.4 Food Chains And Food Webs
A food web shows a complex network of feeding relationships. • An organism may have multiple feeding relationships in an
ecosystem. • A food web emphasizes complicated feeding relationships
and energy flow in an ecosystem.
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13.3 Energy in Ecosystems KEY CONCEPT
Pyramids model the distribution of energy and matter in an ecosystem.
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13.3 Energy in Ecosystems
energy transferred energy lost
An energy pyramid shows the distribution of energy among trophic levels.
• Energy pyramids compare energy used by producers and other organisms on trophic levels.
• Between each tier of an energy pyramid, up to 90 percent of the energy is lost into the atmosphere as heat.
• Only 10 percent of the energy at each tier is transferred from one trophic level to the next.
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13.3 Energy in Ecosystems
Other pyramid models illustrate an ecosystem’s biomass and distribution of organisms.
• Biomass is a measure of the total dry mass of organisms in a given area.
tertiary consumers
secondary consumers
primary consumers
producers
75 g/m2
150g/m2
675g/m2
2000g/m2 producers 2000g/m2
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13.3 Energy in Ecosystems
• A pyramid of numbers shows the numbers of individual organisms at each trophic level in an ecosystem.
tertiary consumers
secondary consumers
primary consumers
producers
5
5000
500,000
5,000,000 5,000,000 producers
• A vast number of producers are required to support even a few top level consumers.