3. 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.
4. 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.
5. Pyramid of biomass
Ecologists draw a
pyramid of biomass by
weighing all the
organisms at each stage
of the food chain.
The mass of producers is
larger than the mass of
consumers to give a
typical pyramid shape
6. 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.
7. The poison dart frog has a brightly coloured toxic skin which puts
off predators.
8. The leaf frog is camouflaged to blend into the background.
9. • 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.
10. 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).
11. Predator-prey relationship
Grouse are birds that live in moorland environment such
as in Scotland. Grouse eat mainly heather, and are prey
for eagles.
heather → grouse → eagle
12. Predator-prey relationship
If there is lots of heather and therefore plenty of
grouse, the eagle population will thrive.
More eagle predators will catch lots of grouse so
after a while the grouse population will fall.
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.
