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Trophic levels in an ecosystem – EcologyTrophic levels
A simple food chain is:
algae → mosquito larvae → dragon fly larvae → perch
All other food chains in an ecosystem can be added together to make a food web. These
stages in a food chain or web are called trophic levels. The arrows show the transfer of
biomass from one trophic level to another.
At the bottom of all food chains is a producer. This is almost always a plant or alga which can
photosynthesise to convert carbon dioxide and water into glucose. This provides all the
biomass for the food chain. Algae are the producers in the food chain above.
The second trophic level in all food chains is an herbivore or omnivore called a primary
consumer. Mosquito larvae are the primary consumers in the above food chain. The third
stage is a carnivore or omnivore which eats the primary consumer. This is called the
secondary consumer and is dragonfly larvae in the above food chain.
- There may be additional carnivorous consumers here which would be called tertiary
and quaternary. The final level is perch, also a carnivore and is often called the top or
apex predator.
Organisms at the tops of food chains have no predators.
Decomposers are bacteria and fungi which breakdown dead plant and animal matter. They
secrete enzymes on the surface of the dead organisms to break the down and then absorb
the digested, smaller food molecules.
Words and there Meaning -
Producers- Green plants - they make glucose during photosynthesis.
Primary consumers- Usually eat plant material - they are herbivores. For example rabbits,
caterpillars, cows and sheep.
Secondary consumers- Usually eat animal material - they are carnivores. For example cats,
dogs and lions.
Predators- Kill for food. They are either secondary or tertiary consumers.
Prey- The animals that predators feed on.
Scavengers- Feed on dead animals. For example, crows, vultures and hyenas are scavengers.
Decomposers- Feed on dead and decaying organisms, and on the undigested parts of plant
and animal matter in faeces.
, Pyramids of biomass
Biomass-
Biomass is living or recently dead tissues. The mass of your body is biomass because you are
alive. Wood is considered biomass because it was recently a plant. Fossil fuels are not
considered biomass because they are the remains of organisms that died millions of years
ago and have been chemically changed from the original living tissue.
Pyramids of biomass-
We can measure the amount of biomass at different trophic levels in a food chain. The total
biomass of each trophic level is often represented as a modified bar chart called a pyramid
of biomass. In a food chain from a healthy ecosystem the biomass at each trophic level must
reduce.
An example of a food chain is:
clover → snail → thrush → sparrowhawks
So in an ecosystem the clover has more biomass than all the snails, which have more biomas
than all the thrushes and so on. We say that pyramids of biomass are always perfectly
shaped. If this is not the case, then the ecosystem is likely to be unhealthy and in danger.
Pyramids of biomass must be drawn with the:
- bars equally spaced around the midpoint
- bars touching
- bar for the producer at the bottom
- length of each bar is proportional to the amount of biomass available at each trophic
level
Transfer of biomass -
The arrows in a food chain show the transfer of biomass from one organism to another.
An example of a food chain is:
maize → locust → lizard → snake
Some of the energy from the Sun absorbed by maize when it photosynthesises is transferred
to the locusts when they eat the plant. So biomass is transferred. Then some of the biomass
in the locust is transferred to the lizards when they are eaten and so on.
Energy transfer is a pyramid of biomass
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