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

• 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

The Ultimate Limit on the Abundance of Life

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.