Page 28 - Science Coursebook

2.3 Ecology

Ecologists are scientists who study organisms in their environment.
This study is called ecology. Like other scientists, ecologists ask

questions and then do experiments to try to find answers.

Investigating camel grazing in Dubai
Large areas of Dubai are desert. Many kinds of plants are adapted
to live in the desert. But, in many places, the number of small
plants is gradually decreasing.
Some ecologists wanted to find out if grazing (feeding) by camels

was causing this decrease. They chose an area in the Dubai Desert
Conservation Reserve where there is a fence several kilometres
long. On one side of the fence, camels are allowed to graze. On the
other side of the fence, only oryx and gazelles graze.
The ecologists marked out 43 pairs of plots. In each pair, one plot
was on the camel side of the fence, and the other plot was on the

oryx side, just opposite the first one. Each plot was the same size.
Then the ecologists counted the number of plants in each plot and
the number of plant species per plot. They calculated the mean A gazelle grazing in the Dubai
numbers per plot. Their results are shown in the table. Desert Conservation Reserve.

Grazed by camels Grazed by oryx and gazelles
Mean number of plants per plot 64 87
Mean number of plant species per plot 4 5

Questions

SE 1 What was the independent variable in the ecologists’ investigation?
SE 2 What were the two dependent variables?
SE 3 State two variables that the ecologists kept constant in their investigation.
SE 4 Write down any conclusions the ecologists can make from their results.
SE 5 Suggest how the ecologists could improve their experiment.

Sampling
In the camel grazing experiment, the ecologists did not count all of the plants
in the whole area on each side of the fence. It would have taken too long.
Instead, they counted the plants in 43 pairs of plots. This is called sampling.

When ecologists use sampling techniques, they must be careful to:
• use a fairly large sample
• place their samples randomly.
If they only used 10 pairs of plots, then their results might not show the true
pattern for the whole area. If they chose the parts of the area where the This student is sampling
vegetation looked most interesting, then once again their results might not the invertebrates that
show the true overall pattern. live in a river.

26 2 Living things in their environment