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Energy in Ecosystems

18.3

Where does the energy in an ecosystem come

from?

Producers provide the energy for organisms in an

ecosystem.

• Producers or autotrophsmake their own food…

• …so, where do producers get their energy from??

The Sun

Producers make their own food by:

• Photosynthesis: process where light is converted to energy in the form of glucose

–Photoautotrophs

• Chemosynthesis: the use of chemicals to make food

–Chemoautotrophs

Energy flows through Ecosystems from producers

to consumers• Consumers get their energy from

eating living or once-living resources

• Consumers are also called heterotrophs because they feed on many different things

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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

Food Chains & Food Webs

Food chains and food webs are two types of feeding

relationships and model the flow of

energy in an ecosystem.

A food chain is a model that shows a sequence of feeding relationships.

• Simple path through an ecosystem

• A food chain follows the connection between one producer and a single chain of consumers within an ecosystem.

A food web contains several food chains.

• An organism may have several feeding relationships in an ecosystem.

• A food web emphasizes complicated feeding relationships and energy flow in an ecosystem.

• More realistic model

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How Many Chains are in

this web?

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• Specialists are consumers that primarily eat one specific organism or a very small number of organisms.

• Generalists are consumers that have a varying diet.

Trophic levels are the nourishment levels in a food chain.

1st Level - Producers

2nd Level - Primary consumers are herbivores that eat producers.

3rd Level - Secondary consumers are carnivores that eat herbivores.

4th Level - Tertiary consumers are carnivores that eat secondary consumers.

Primary Consumer

Secondary Consumer

TertiaryConsumer

–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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Food Chain

Producer (trapped

sunlight & stored food)

1st order Consumer

2nd Order Consumer

3rd Order consumer

4th Order Consumer

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Food Web

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Food Chains Show Available Energy

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10% Rule• Energy flows up the food chain from

the lowest trophic level to the highest.• Only 10% of the energy is transported

from 1 trophic level to the next.• Ex. producer � primary consumer• 10% of the energy is transferred to

the consumer while the other 90%is either used by the organism or lost as heat to the atmosphere

Pyramid Models

Pyramids model the distribution of energy and matter in an ecosystem.

• 3 Types of pyramids:

-energy pyramid

-biomass pyramid

-pyramid of numbers

Energy Pyramid• Shows how

available energy is distributed among trophic levels in an ecosystem

• Outward arrows indicate energy lost as heat and waste

• 10% transfers to next level

energy transferredenergy

lost

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Energy Pyramid

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Biomass Pyramid• Compares the biomass of different trophic

levels within an ecosystem

• Biomass: 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/m2producers 2000g/m2

Pyramid of Numbers

• Shows the number of individual organisms at each trophic level in an ecosystem

tertiary

consumers

secondary

consumers

primary

consumers

producers

5

5000

500,000

5,000,0005,000,000producers

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Changing one factor in an ecosystem can affect many other factors.

• Biodiversity: variety of life

-the more biodiversity in an ecosystem, the more complex it is

• Keystone species: a species that has an unusually large effect on an ecosystem

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• Beavers are a keystone species because they create an ecosystem used by a wide variety of species

creation ofwetland

ecosystem

increased waterfowl

Population

increased fish

populationnesting sites for

birds

keystone species