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