Chapter 9: Biological
Productivity and Energy Flow
How much can we grow?
• Determining how much organic matter can
be produced in any time period.
– Farm production
– Number of people on Earth
– Whales in ocean
• Many factors limit growth
– Ultimate limit is energy flow
Biological Production
• Biomass- the total amount of organic matter
on Earth or in any ecosystem or area.
– Usually measured as the amount per unit
surface area
• Biological production- the capture of usable
energy from the environment to produce
organic compounds in which that energy is
stored.
Biological Production
• Change in biomass over a given time is
called net production.
• Three measures used for biological
production
– Biomass
– Energy stored
– Carbon stored
Net production
Two Kinds of Biological
Production
• Autotrophs
– Make their own organic matter from energy
source and inorganic compounds
– Primary production
– Most photosynthesize, some chemoautotrophs
• Heterotrophs
– Cannot make their own organic compounds and
must feed on other living things
– Secondary production
Use of energy
• Use of energy from organic matter by most
heterotrophic and autotrophic organisms
done by respiration.
– Organic matter combines with oxygen
– Releases energy, carbon dioxide and water
• Respiration- the use of biomass to release
energy that can be used to do work.
Gross and Net Production
• Production of biomass and its use as a
source of energy
– 1. An organism produces organic matter w/in
its body. (gross production)
– 2. It uses some of this new organic matter as a
fuel for respiration.
– 3. It stores some of the newly produced organic
matter for future use. (net production)
Gross and Net Production
• Net production = Gross production - respiration
Energy Flow
• Most of the time energy is invisible to us
– With infrared film we can see difference
between warm and cold object
– Warm object appear red
– Cool objects appear blue
Birch forest in New Hampshire
Regular film
Infrared film
A near by rocky outcrop
Regular film
Infrared film
Energy flow
• All life requires energy.
– The ability to do work
• Ecosystem energy flow– the movement of energy through an ecosystem
from the external environment through a series
of organisms and back to the external
environment.
Energy Flow
• Energy enters an ecosystem by two
pathways.
– 1. Energy fixed by organisms
– 2. Transfer of heat energy by air, water, soil
and warm living things.
The Ultimate Limit on the
Abundance of Life
• Laws of thermodynamics
• First law = Law of conservation of energy
– In any physical or chemical change, energy is
neither created nor destroyed but merely
changed from one form to another.
Impossible ecosystem because of 2nd law of thermodynamics
The Ultimate Limit on the
Abundance of Life
• Energy must continually be added to an
ecological system in a usable form.
– Because inevitably degraded into heat
– Net flow of energy is a one way flow
• Thermodynamic system
– Energy source
– Ecosystem (intermediate system)
– Energy sink
Energy Efficiency
• As energy flows through a food web, it is
degraded, and less and less is useable.
• Energy efficiency- the ratio of output to
input
– The amount of useful work obtained from some
amount of available energy
Energy Efficiency and Transfer
Efficiency
• Trophic-level efficiency- the ratio of
production of one trophic level to the
production of the next trophic level.
–
–
–
–
Never very high
1-3% in natural ecosystems
10% may be maximum
90% of all energy lost as heat
Energy Flow in an Old-Field
Food Chain
• Meadow mice feed on grasses and herbs.
• Weasels feed on mice.
• Most of the energy used in respiration
– 15% of vegetation gross production
– 68% of energy taken up by mice
– 93% of energy taken up by weasels
Energy Flow in a Stream or River
• The amount of organic matter produced by
algae is small relative to amount of input by
dead leaves and vegetation falling into
stream.
– Supports detritivores
– Amazon Basin floodplain high production of
herbivores fish
Energy Flow in Ocean
Ecosystems
• Several ocean food chains start with
phytoplankton.
• One continues near the surface
– Variety of animals feed on those algae
– Baleen whales and other animals spend much of
their time in upper ocean.
• Other occurs deep in the ocean
– Fecal matter and dead organisms sink to sea
floor
Chemosynthetic Energy Flow in
the Ocean
• Chemosynthetic organisms make their own
food from energy in sulfur compounds.
– Sulfur-laden water is emitted from hot water
vents
– Rich biological communities surround the vents
– Clams, mussels, crabs, limpets, fish, octopuses
and giant worms.