02 Energy Flow through Ecosystems

Energy Flow Through Energy Flow Through EcosystemsEcosystems

• Inside the cell, source of energy is Inside the cell, source of energy is adenosine triphosphate (ATP)adenosine triphosphate (ATP)

• The source of energy for making ATP is The source of energy for making ATP is other organic molecules such as other organic molecules such as carbohydrates, lipids and proteins carbohydrates, lipids and proteins (respiration)(respiration)

• Energy is stored in carbohydrates, Energy is stored in carbohydrates, lipids and proteins through lipids and proteins through photosynthesisphotosynthesis

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Energy flowEnergy flow

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Heat

Heat

Heat

Heat

Heat

Heat Heat Heat

Detritivores (decomposers and detritus feeders)

First Trophic Level

Second TrophicLevel

Third Trophic Level

Fourth Trophic Level

Solar energy

Producers(plants)

Primary consumers(herbivores)

Secondary consumers(carnivores)

Tertiary consumers

(top carnivores)

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Heat

Heat

Heat

Heat

Heat

DecomposersTertiary

consumers(human)

Producers(phytoplankton)

Secondaryconsumers

(perch)

Primaryconsumers

(zooplankton)

10

100

1,000

10,000Usable energy

Available atEach tropic level(in kilocalories)

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• ProducersProducers – autotrophic organisms; – autotrophic organisms; organisms that obtain its food from inorganic organisms that obtain its food from inorganic sources by photosynthesis or chemosynthesissources by photosynthesis or chemosynthesis

• ConsumersConsumers – heterotrophic organisms; – heterotrophic organisms; organisms that obtain its food in organic organisms that obtain its food in organic form, either directly or indirectly from that form, either directly or indirectly from that which has been synthesised by producerswhich has been synthesised by producers

• Decomposers/DetritivoresDecomposers/Detritivores – feed on – feed on detritus (dead organisms and waste material, detritus (dead organisms and waste material, such as dead leaves, faeces and urine) such as dead leaves, faeces and urine)

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Scavengers

Powder broken down by decomposers into plant nutrients in soil

Bark beetle engraving

Decomposers

Long-horned beetle holes

Carpenter ant

galleries

Termite and

carpenter ant work Dry rot

fungus

Wood reduced to powder

Mushroom

Time progression

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Food chains and food websFood chains and food webs

• Food chainFood chain – the way in which energy – the way in which energy flows from producer to consumersflows from producer to consumers

• Food webFood web – inter-relationships – inter-relationships between many food chainsbetween many food chains

• Trophic levelTrophic level – the level in a food – the level in a food chain at which an organism feeds chain at which an organism feeds

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Arrows indicate the direction in which the energy flowsArrows indicate the direction in which the energy flows

Food WebFood Web

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HumansBlue whale Sperm whale

Crabeater seal

Elephant seal

Killer whale

Leopard seal

Adelie penguins Emperor

penguin

Petrel FishSquid

Carnivorous plankton

Krill Herbivorous plankton

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• HerbivoresHerbivores – are always – are always primary consumersprimary consumers

• CarnivoresCarnivores – feed at several – feed at several different trophic levels in different trophic levels in different food chainsdifferent food chains

• Omnivores Omnivores – animals which – animals which regularly feed as both primary regularly feed as both primary and higher-level consumersand higher-level consumers

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Energy loss along food chainsEnergy loss along food chains

• Energy is lost as heat when energy is Energy is lost as heat when energy is transferred from one form, or from one transferred from one form, or from one system, to anothersystem, to another

• Only small percentage of sunlight is Only small percentage of sunlight is converted into chemical energy because:converted into chemical energy because:– Some sunlight misses leavesSome sunlight misses leaves– Some sunlight reflected from surfaces of leavesSome sunlight reflected from surfaces of leaves– Some sunlight passes through leavesSome sunlight passes through leaves– Chlorophyll only absorbs certain wavelengths of Chlorophyll only absorbs certain wavelengths of

lightlight– Energy losses as energy absorbed by chlorophyll is Energy losses as energy absorbed by chlorophyll is

transferred to carbohydrates during photosynthesis transferred to carbohydrates during photosynthesis

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• Almost half of the chemical potential Almost half of the chemical potential energy stored by plants is used by the energy stored by plants is used by the plants themselves (released through plants themselves (released through respiration/used for active transport)respiration/used for active transport)

• Losses between plants and primary Losses between plants and primary consumer:consumer:– Not all parts of plants available to be eatenNot all parts of plants available to be eaten– Not all parts eaten are digestibleNot all parts eaten are digestible– Energy losses as heat within consumer’s Energy losses as heat within consumer’s

digestive systemdigestive system

• Similar losses occur at each trophic Similar losses occur at each trophic levellevel

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ProductivityProductivity• The rate at which plants convert light The rate at which plants convert light

into chemical potential energy – into chemical potential energy – productivity or primary productivity or primary productivityproductivity

• Kilojoules of energy transferred per Kilojoules of energy transferred per square metre per year (kJ msquare metre per year (kJ m-2-2 year year-1-1))

• Gross primary productivityGross primary productivity – total – total quantity of energy converted by quantity of energy converted by plants in this wayplants in this way

• Net primary productivityNet primary productivity – energy – energy which remains as chemical energy which remains as chemical energy after the plants have supplied their after the plants have supplied their own needs in respirationown needs in respiration

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