Enrgy and Nutrient Flow

Energy flow in ecosystems

Transfer of energy from the sun through producers to consumers in a unidirectional flow

Main energy source

Sunlight (solar energy)

Unidirectional flow

Energy flows one way because it is lost as heat at each trophic level

10% rule

Only about 10% of energy is transferred to the next trophic level; 90% is lost

Energy loss reasons

Respiration (heat), movement, faeces, uneaten parts

Trophic level

Position of organism in food chain or food web

Producer (autotroph)

Converts solar energy into chemical energy via photosynthesis

Consumer

Organism that obtains energy by feeding on others

Decomposer

Breaks down dead organic matter and recycles nutrients

Food chain

Linear pathway showing energy transfer

Food web

Interconnected food chains showing feeding relationships

Grazing food chain

Starts with living plants (producers)

Detritus food chain

Starts with dead organic matter

Bioaccumulation

Build-up of toxic substances in organisms from the environment

Biomagnification

Increase in concentration of toxins at higher trophic levels

Reason biomagnification occurs

Persistent, fat-soluble, biologically active pollutants accumulate in tissues

Example pollutant effect

Top predators have highest toxin concentration due to trophic transfer

Ecological pyramids

Diagrams showing energy, biomass, or numbers at trophic levels

Pyramid of numbers

Shows number of organisms per trophic level per unit area

Shape varies

Can be upright or inverted depending on ecosystem

Pyramid of biomass

Shows total dry mass of organisms per trophic level

Terrestrial biomass pyramid

Upright (producers have highest biomass)

Aquatic biomass pyramid

Often inverted (phytoplankton < consumers due to rapid turnover)

Biomass

Total dry mass of living organisms in an ecosystem

Pyramid of energy

Shows energy available at each trophic level per unit time

Energy pyramid shape

Always upright due to energy loss at each transfer

Example energy values

Sun → 1,000,000 J → producers 10,000 J → primary consumers 1,000 J → secondary consumers 100 J → tertiary 10 J

Productivity

Rate of production of organic matter in an ecosystem per unit time

Primary productivity

Rate at which producers convert energy into biomass

Secondary productivity

Rate at which consumers store energy as biomass

Gross Primary Productivity (GPP)

Total energy captured by photosynthesis

Net Primary Productivity (NPP)

Energy stored in plant biomass available to consumers

NPP formula

NPP = GPP − respiration

Units of productivity

g m⁻² day⁻¹ or kg m⁻² yr⁻¹

Importance of NPP

Represents energy available to all higher trophic levels

Energy efficiency conclusion

Short food chains are more efficient than long ones

Human energy implication

Eating plants (e.g. crops) provides more usable energy than eating animals