1. ProductivityProductivityProductivityProductivity
• Energy Flow begins with PRIMARYPRIMARYPRIMARYPRIMARY PRODUCTIVITYPRODUCTIVITYPRODUCTIVITYPRODUCTIVITY, the amount
of light energy converted to chemical energy (stored in organic molecules)
by an ecosystem's autotrophs over a given period of time via the process
of photosynthesis.
• GROSSGROSSGROSSGROSS PrimaryPrimaryPrimaryPrimary ProductivityProductivityProductivityProductivity (GPP)(GPP)(GPP)(GPP) - Total primary productivity
• RESPIRATIONRESPIRATIONRESPIRATIONRESPIRATION (R)(R)(R)(R) - Energy used to do work in the organism (lost
as entropy)
• NETNETNETNET PrimaryPrimaryPrimaryPrimary ProductivityProductivityProductivityProductivity (NPP)(NPP)(NPP)(NPP) - Total primary productivity less
the
energy used for respiration
2. Primary productivity (always expressed as a RATE) can be expressed as
• ENERGYENERGYENERGYENERGY per unit area per unit time (e.g., Joules/m2
/year)
or
• BIOMASSBIOMASSBIOMASSBIOMASS, the dry weight of vegetation added to an ecosystem per
unit area per unit time (e.g., grams/m2
/year).
STANDINGSTANDINGSTANDINGSTANDING CROPCROPCROPCROP BIOMASSBIOMASSBIOMASSBIOMASS is the dry weight of vegetation in an
ecosystem at any given "snapshot moment" in time. It is not the same as
primary productivity: it's not a rate!Energy flow is never 100% efficient.
This results in a pyramidpyramidpyramidpyramid ofofofof productivityproductivityproductivityproductivity.
The efficiency with which trophic levels convert energy from the previous
trophic levels varies among ecosystems, but usually range between 5% -
20%.
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