Trophic levels
• Determines the pathways of energy
flow and nutrient cycling (more on this
later)
• Different species in the ecosystem are divided
into different trophic levels depending on
what they eat
• There are 5 main levels
Trophic levels
Level 1 – Producers
• The bases of food chains
• Get their energy from the sun
• E.g. Plants
Level 2 – Primary Consumers
• Herbivores
• Eat a range of plant material
Trophic level
Level 3 – Secondary Consumers
• Organisms that eat Primary consumers
(Herbivores)
Level 4 – Tertiary Consumers
• Eat Secondary consumers
Level 5 – Quaternary Consumers
• Eat Tertiary consumers
Food chains
• Sequence of organisms, each of which is a
source of food for the next.
• Always begins with a producer
Plant
Caterpillar
Bird
Cat
• Animals with the same number of links to
other organisms are on the same trophic level
Food chains/food webs
• In real life a particular herbivore may eat more
than one type of plant or a carnivore may eat
lots of different herbivores
• Hence a more accurate way of showing
trophic levels is by using a food web
Cat
Lizard
Snail
Bird
Worm
Plants
Caterpiller
Pyramids
• Another way of representing a food
chain
1. Pyramid of numbers
2. Pyramid of biomass
1. Pyramid of numbers
• Number of each type of organism at each
trophic level
• Not always accurate as does not take the size
of organism at each level into account
– E.g. One large tree could support thousands of
caterpillars.
Pyramid of numbers
10 Cats
500 Birds
30,000 Caterpillars
1,000 Flax bushes
2. Pyramid of Biomass
• More accurate method
• The weight of living matter at each level is
measured
• Most accurate to use the DRY matter weight
Pyramid of Biomass
500 kg Humans
1 ton
trout
300 tons shrimp
1,000 tons of seaweed
Ways in which food chains and webs
can be affected.
1. Removing one part of the food chain
2. Biological magnification
3. Introducing an exotic species
4. Removal of too much of an organism
Ways in which food chains and webs
can be affected.
• Removing one part of the food chain
– Happens through over farming, fishing and cutting
down of native forest.
– If you remove too much of the producer, then the
rest of the food chain suffers
Ways in which food chains and webs
can be affected.
• Biological magnification
– Concentrations of poison (e.g. mercury, DDT)
increase as it moves up the food chain or up the
pyramid
– Top predator gets the highest concentrations
Ways in which food chains and webs
can be affected.
• Introducing an exotic species
– Rabbits
– Possums
– Deer
Ways in which food chains and webs
can be affected.
• Removal of too much of an organism
– Can make an ecosystem unsustainable
– E.g. Over fishing – not enough older fish for
reproduction
– E.g. Over farming – Nutrients are not returned to
the soil therefore it becomes useless