Week 3: Lead Lessons
Energy in ecosystems
Food chain model
Based on TROPHIC LEVELS
Producers => make their own food via photosynthesis using light energy
Primary consumers => organisms that eat producers [herbivores]
Secondary consumers => organisms that feed on primary consumers [carnivores]
Tertiary consumers => organisms that feed on other carnivores [top predator]
Decomposers => rarely included in a food chain, final trophic level
Break down remains of other organisms and return mineral nutrients to soil
Food webs
MORE REPRESENTATIVE
If organisms only eat one thing => VULNERABLE should anything threaten food source
Most organisms eat multiple things => INCREASES STABILITY
Ecological pyramids
1. Pyramids of numbers
Looks at total number of each organism at each trophic level
Numbers decreases as we go higher
DOESN’T ACCOUNT FOR SIZE (single rose bush supporting large population of aphids)
2. Pyramids of biomass
Takes into account MASS/SIZE of organisms at each trophic level
Difficult to measure due to water content of organisms being variable
(transpiration/drinking/urination)
DRY MASS more accurate but involves destruction of the material
Pyramids of energy
, Pyramids of biomass only give snapshot of single moment in time => REPRODUCTION RATES NOT
ACCOUNTED FOR
Most accurate way to represent turnover of organisms
Amount of energy stored in organism DECREASES at every trophic level along food chain
Very difficult to measure so biomass often used
Losses in a food chain
Animals eat plants => only relatively small proportion of this becomes new animal material
Losses include:
Not all broken down/digested so some expelled as unused in faeces
Respiration – exothermic reaction that produces ATP and heat energy
Lost in metabolic waste like urea
Energy not passed on is dissipated into surroundings adding to internal energy store of universe
PROCESS OF MAKING A NEW ANIMAL BIOMASS => SECONDARY PRODUCTION
Often said that 10% of energy is passed on but it varies massively (2-24%)
Energy transfer between trophic levels
Starting point in all ecosystems is LIGHT ENERGY from sun in reactions of
photosynthesis
Rate of photosynthesis determines RATE AT WHICH PRODUCERS MAKE
NEW BIOMASS AND RATE OF NEW BIOMASS SYNTHESIS IN HIGHER
TROPHIC LEVELS
Only small quantity of energy from sunlight results in production of new
plant material
Gross primary productivity and net primary productivity
Energy in ecosystems
Food chain model
Based on TROPHIC LEVELS
Producers => make their own food via photosynthesis using light energy
Primary consumers => organisms that eat producers [herbivores]
Secondary consumers => organisms that feed on primary consumers [carnivores]
Tertiary consumers => organisms that feed on other carnivores [top predator]
Decomposers => rarely included in a food chain, final trophic level
Break down remains of other organisms and return mineral nutrients to soil
Food webs
MORE REPRESENTATIVE
If organisms only eat one thing => VULNERABLE should anything threaten food source
Most organisms eat multiple things => INCREASES STABILITY
Ecological pyramids
1. Pyramids of numbers
Looks at total number of each organism at each trophic level
Numbers decreases as we go higher
DOESN’T ACCOUNT FOR SIZE (single rose bush supporting large population of aphids)
2. Pyramids of biomass
Takes into account MASS/SIZE of organisms at each trophic level
Difficult to measure due to water content of organisms being variable
(transpiration/drinking/urination)
DRY MASS more accurate but involves destruction of the material
Pyramids of energy
, Pyramids of biomass only give snapshot of single moment in time => REPRODUCTION RATES NOT
ACCOUNTED FOR
Most accurate way to represent turnover of organisms
Amount of energy stored in organism DECREASES at every trophic level along food chain
Very difficult to measure so biomass often used
Losses in a food chain
Animals eat plants => only relatively small proportion of this becomes new animal material
Losses include:
Not all broken down/digested so some expelled as unused in faeces
Respiration – exothermic reaction that produces ATP and heat energy
Lost in metabolic waste like urea
Energy not passed on is dissipated into surroundings adding to internal energy store of universe
PROCESS OF MAKING A NEW ANIMAL BIOMASS => SECONDARY PRODUCTION
Often said that 10% of energy is passed on but it varies massively (2-24%)
Energy transfer between trophic levels
Starting point in all ecosystems is LIGHT ENERGY from sun in reactions of
photosynthesis
Rate of photosynthesis determines RATE AT WHICH PRODUCERS MAKE
NEW BIOMASS AND RATE OF NEW BIOMASS SYNTHESIS IN HIGHER
TROPHIC LEVELS
Only small quantity of energy from sunlight results in production of new
plant material
Gross primary productivity and net primary productivity
