SKILL FOCUSPredictingHypothesizingPerforming and recordingAnalyzing and interpretingCommunicating resultsInvestigation 15 • B
530 MHR • Unit 5 Population Dynamics
Pre-lab Questions
What is meant by the phrase “tragedy of the
commons”?
What does it mean when an activity is said to
be sustainable?Problem
How can the members of a community prevent
destruction or degradation of a shared resource?Prediction
Predict how shared resources will be affected by
community members over a specific time period,
and suggest methods for sustaining that resource.Materials
large number of white pebbles, marbles, beans, or other
small objects
large number of red pebbles, marbles, beans, or other
objects (they need not be red, but must be different in
colour and similar in size to the white objects)opaque bag (or box) for each communityProcedure
1.Divide the class into groups of four. Each group will
represent a community.
2.Place 16 white pebbles in each community bag. The
white pebbles represent one parcel of farmland.
3.Give each community member a large handful of
red pebbles. Each red pebble represents the use
of chemical fertilizers and pesticides.
4.For each white pebble drawn from the bag by a
community member, a red pebble will be placed
in the bag.
5.Each member of the community will, one by one
and in his or her turn, extract one or more pebbles
without looking in the bag. At least one white
pebble must be drawn if the person is to survive;
if a member fails to get a white pebble, he or she
has lost his/her parcel of land and cannot continue
play. Each member may take as many pebblesHow Can the Tragedy of the
Commons Be Avoided?
When a resource is overused, it often becomes damaged in such a way that it
becomes less available (or completely unavailable) to members of a community.
To use resources in a sustainableway, they must be managed carefully so they
are not degraded and they remain useable by future generations.pesticides, fertilizers, oil, and other chemicals)
must go somewhere. If they do not decompose
naturally, they end up in the water or soil.
When organic materials from sewage and food
processing plants, paper mills, and other sources
enter the water, they serve as nutrients for the
bacteria that degrade them. A substantial influx
of these materials can cause rapid growth of the
bacterial population. The cellular respiration of
this large number of bacteria can deplete oxygen
from the water and harm other aquatic organisms.
Many inorganic nutrients (such as nitrates and
phosphates from fertilizers and sulfates from laundry
detergents) also end up in water. This nutrient
abundance can lead to excessive growth of algae
and/or plants (called an algal bloom), which
similarly rapidly depletes the available oxygen in
the water (due to the high demand for oxygen to
support cellular respiration). This then causes anincrease in the death rate of the algae and plants. The
large amounts of dead material are then decomposed
by bacteria, which further deplete the oxygen supply,
leading to the death of some aquatic animals.
Figure 15.21 on page 531 shows one such situation.
Some pollutants, such as oil, gasoline, heavy metals,
and pesticides, are toxic to many forms of life.
They cannot be degraded by bacteria easily and
remain in the environment for long periods of time.
These are the types of substances that are involved
in biological magnification, as described in Chapter- Heat is another pollutant, creating the thermal
pollution that affects many rivers and lakes.
Produced by power plants and other industrial
processes, this added heat reduces the amount of
oxygen that can be dissolved in water and may
eventually cause harm to aquatic organisms.
Many of the pollutants described above can
have serious and immediate effects on human