Download Productivity Review and Calculations

Productivity Review and
Calculations
Recap of Definitions!
Key term
Definition
Productivity
The total gain in energy of the producers.
Primary Productivity
The total gain in energy/biomass per unit area per
unit time.
Secondary Productivity
Production per unit area per unit time
Gross Productivity (GP)
The gain in energy/biomass per unit area per unit
time remaining after allowing for respiration losses
which is passed onto the herbivores.
Gross Primary
Productivity (GPP)
The rate at which energy/biomass is formed through
photosynthesis
Net Productivity (NP)
The gain in energy/biomass per unit time remaining
after allowing for respiration (R) loses.
Net Primary
Productivity (NPP)
The rate at which primary material is synthesised
into animal tissue per unit area in a given time.
Important Calculations

How do we calculate GPP?
GPP = NPP + R

How do we calculate NPP?
NPP = GPP – R

How do we calculate GSP:
GSP = food eaten – faecal losses
Or… NSP + R

How do we calculate NSP
NSP = GSP – R
Calculating Productivity Values

Some easy ones to start you off!

What is the % energy from sunlight that is fixed as GPP
if the total energy from the sun in 3 x 106 and the gross
primary productivity = 2.8 x 104?

What is the GPP of an ecosystem if the NPP is 1660
kJm-2yr-1 and the energy lost during respiration is 573
kJm-2yr-1 ?

What is the NPP if the GPP is 2700 kJm-2yr-1 and the
energy used in respiration is 1850 kJm-2yr-1?
Calculating Productivity Values
Now for some slightly harder ones!
Energy Flow Diagrams
Energy flow diagrams illustrate energy flow
through communities and include values for
respiratory losses and energy flow through
the decomposers
Information from energy flow diagrams can be used to
calculate ecological efficiencies
Ecological Efficiency is the net production of new
biomass at each trophic level as a percentage of the
total energy flowing through that trophic level
Therefore, for photoautotrophs, photosynthetic
efficiency is determined as:
Photosynthetic Efficiency =
Net production ÷ Light Energy Absorbed
Use information from the energy flow diagram to:
• Explain the meaning of the term Gross Primary Production
• Explain the meaning of the term Net Primary Production
• Calculate the Photosynthetic Efficiency of the phytoplankton
Gross Primary Production is the total energy fixed
by photoautotrophs during photosynthesis
Net Primary Production is the energy stored as
biomass (gross production – energy lost as heat
in respiration)
Photosynthetic
Efficiency =
3.7 x 104
------------ x 100
172 x 104
= 2.15%
Photosynthetic
efficiency = 1.3%
GPP =
24 x106 kJ m-2year-1
114 x 103 kJ m-2year-1
NPP =
800 kJ m-2year-1
NPP =
69.7 x 103 kJ m-2year-1
NPP =
200 kJ m-2year-1