Food chains/webs and trophic levels

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 levelLevel 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

• Animals with the same number of links to other organisms are on the same trophic level

Plant

Caterpillar

Bird

Cat

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 Worm

Bird

Caterpiller

Plants

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

1,000 Flax bushes

30,000 Caterpillars

500 Birds

10 Cats

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

1,000 tons of seaweed

1 ton trout

300 tons shrimp

500 kg Humans

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