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Energy Flow in Ecosystems
GISAT 112
Objectives
• Define the terms ecosystem and ecology• Describe how energy and matter flow in an
ecosystem• Do calculations to determine the productive
efficiencies of an ecosystem• Explain the concept of an energy pyramid
Ecology
• Ecology - the study of relationships between organisms and their environment (Greek oikos-house, and logos - study of)
• Ecosystems - a community of different species interacting with one another and with their nonliving environment of matter and energy
• The size of an ecosystem is somewhat arbitrary - defined by the area we wish to study.
What sustains life on earth?
1) Energy flow from sun
2) Cycling of matter
3) Gravity
• 6CO2 + 6H2O + solar energy ==> C6H12O6 + 6O2
• C6H12O6 + 6O2 ==> 6CO2 + 6H2O + energy
Simplified Ecosystems
In simplest terms, all ecosystems have 3 basic components:
autotrophs (producers)
consumers (herbivores, carnivores, and decomposers)
abiotic matter
Draw these 3 components as the points of a triangle. • What interactions occur between them? • What crosses the boundaries of the triangle? • Can you name these processes?
Producer-Consumer Chains• Producer-consumer chains (or webs) drive the
flow of matter and energy– Producer (autotroph)– Consumer (heterotroph)
Primary Production
• Gross primary production (GPP) is the ability of producers to produce carbon compounds from solar energy. Units are energy per area per time (usually kcal/m2/year).
• Net primary production (NPP), is the amount of energy that remains after accounting for energy used by producers.
• NPP = GPP – Energy used in respiration
Average NPP for Various Ecosystems
Secondary Production
• Not all energy stored in plants is consumed by herbivores—some just can’t be accessed
• If a herbivore does capture some of the NPP energy, not all of that energy is assimilated into the herbivore’s body.
• The energy consumed is used for maintenance, growth, and reproduction—or passed as waste.
• The stored energy is considered secondary production for the next trophic level
An Example of Secondary Production Energy Model
Ingestion
Respiration
Waste
Production
I = P + R + WAssimilation (A) = P + R
Production Efficiencies
• A/I = assimilation efficiency; efficiency of consumer in extracting energy from the food it consumes.
• P/A = production efficiency; efficiency of consumer in incorporating the assimilated energy into new tissue growth, or secondary production.
Food Chains and Energy Flow
Energy Flow for a Grassland
Energy Pyramids
Pyramid of Numbers
Pyramid of Biomass
Pyramid of Energy Flow
Energy needed to support a Cow?
70
14Growth
1000 Produced
800Unavailable
130Waste
56Respiration
Energy Balance of a Cow
200 Consumed