Pyramid of biomass

How do living things in a community depend on each other?

To study the realtionship between populations in a food chain, we count the organisms and draw a diagram called a pyramid of numbers.

This pyramid shows a typical shape, with lots of producers below and just a few carnivores at the top.

Drawing pyramids

This pyramid is different because there is only one oak tree with lots of caterpillars living off it.

The oak tree is one organism, but it is very large. To give a more realistic idea of the feeding relationship we use another pyramid called a pyramid of biomass.

Ecologists draw a pyramid of biomass by weighing all the organisms at each stage of the food chain.

Pyramid of biomass

The mass of producers is larger than the mass of consumers to give a typical pyramid shape

Predators and prey

Predators are organisms high up the food chain. They are good hunters, well adapted to finding, catching and killing their prey.

Prey animals are well adapted for detecting and avoiding predators.

The poison dart frog has a brightly coloured toxic skin which puts off predators.

The leaf frog is camouflaged to blend into the background.

• The golden eagle is well adapted as a predator.

• Large forward facing eyes make it easier to spot potential prey.

• The beak is hooked and sharp so easily tears flesh from the body of its prey.

• Gliding flight is silent.• Talons kill by piercing

vital organs or snapping bones.

Predator-prey relationship

In any environment the relative number of predator

and prey are constantly changing, depending on

environmental factors such as the availability of

green plants (producers).

Grouse are birds that live in moorland environment such

as in Scotland. Grouse eat mainly heather, and are prey

for eagles.

heather → grouse → eagle

Predator-prey relationship

If there is lots of heather and therefore plenty of grouse, the eagle population will thrive.

Predator-prey relationship

Then there are fewer grouse for the eagles to eat, so after a while the number of eagles falls too. This allows the number of grouse to increase again, and so the cycle continues.

More eagle predators will catch lots of grouse so after a while the grouse population will fall.

Predator-prey relationship graph

heather → grouse → eagle