Activity 4: Teaching Tips
The graph on student page 530 is available as
Blackline Master Ecology 4.1: Changes in Reindeer Population.
Graph paper is available as
Blackline Master Ecology 4.2: Graph of Human Population Growth.
You may wish to use Assessment Rubric for Graphs available at the end
of Activity 3 in this Teacher's Edtion to assess the students' graphs. Provide students with other examples of growth rate to illustrate both positive
and negative growth rates. For example: the deer population in an area was
75 in 2000. In 2005, the population was 85.
What was the average rate of growth? (85 - 75 = 10 10/5 = 2)
Ask the students to speculate how biologists might go about counting the trees
on a hillside. (They probably estimated by counting the number of trees in several sample areas and then extrapolating the information.) Emphasize the concept of unit area in defining a growth in population.
It may be a small area such as the water droplet on moss, or a larger area
such as a pond, or an area as large as the Earth itself.
You may want to introduce density calculations at this time. The rate at which
the density of a population changes is equal to the change in density divided
by the change in time.
Ask students why, when considering carrying capacity, we must think
of the whole Earth for humans but not for pigeons or pine trees.
(Pines and pigeons are widely spread over the Earth, but they are not as
ubiquitous as people. Moreover, human activities do not affect only the parts
of the biosphere humans inhabit but all parts, for example the stratosphere
and the oceans.)
You may provide the students with the following questions to assess their understanding of the reading.
1. How do you calculate the rate of change in a population?
(You divide the amount of change by the amount of time
for the change to take place.)
2. What are the four limiting factors that affect a population?
(birthrate, death rate, immigration, and emigration)
3. What does carrying capacity mean? (The maximum number of individuals that a given environment can support)
4. What is the difference between an open and a closed population? (In an open population all four factors that affect population size are
functioning. In a closed population, only birthrate and death rate affect population size.)
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