Photosynthesis Limiting Factors
• >90% of sun’s energy is reflected or absorbed by clouds/dust
• Not all wavelengths of sunlight can be used
• Light may not fall on a chlorophyll molecule
• Low carbon dioxide levels
Gross Primary Productivity
• The total quantity of energy that the plants in a community convert to organic matter
• Plants use 20~50% of energy as respiration, where very little of it is stored
• The rate at which a plant stores energy is the net primary production

Net Primary productivity = Gross Primary – Respiratory Losses
Energy Loss by Consumers

• Only 10% of this plant food stored is used by primary consumers for growth
o The low percentage is due to cellulose not being able to be broken down
• Secondary and tertiary consumers ae more efficient transferring about 20% available from the prey into their bodies
• Energy is lost through:
o Movements
o Some parts are not eaten (e.g. bones)
o Some parts are indigestible (e.g. cellulose)
o Excretory materials
o Heats from respiration
o Body temperature

Calculating the efficiency of energy transfers
• Data is given at each available trophic level
• The amount of energy available is commonly measured in kJ m-2 year-1

Energy Transfer Efficiency = Energy Available after the transfer x100
Energy Available before the transfer
e.g. Calculate the efficiency of the transfer of energy from a producer to a tertiary consumers
Trophic Level Productivity (kJ m-2 year-1)
Producers 9,000
Primary Consumers 1,500
Secondary Consumers 120
Tertiary consumers 12

12 x100 = 0.13%

Ecological Niche
• The role of a species within its habitat following:
o Biotic Interaction
o Abiotic Interaction
• It includes the position of the species within a food chain