Activity 4: For You To Do
Teaching Suggestions and Sample Answers

Part A: Reindeer Population
1. For this step, suggest that students read the numbers from the graph to the nearest 100. a) In 1920 the size of the population was about 300. The difference between 1911 and 1920 was +250. The average annual increase was about 28.
b) In 1930 the size of the population was about 500. The difference between 1920 and 1930 was +200. The average annual increase was about 20.
c) In 1938 the size of the population was 2000. The difference between 1930 and 1938 was +1500. The average annual increase was about 187.
d) The increase was the greatest from 1930 to 1938.
e) The greatest number was 2000 in 1938.
f) The difference between 1938 and 1950 was +1992. The average annual decrease was 166.

Teaching Tip
The graph on student page 530 is available as Blackline Master Ecology 4.1: Changes in Reindeer Population

2. a) Probably not. St. Paul Island is more than 323 km from the mainland. Reindeer are strong swimmers, but the distance is too great for emigration or immigration to have a major effect.
b) Population growth is exponential. Exponential growth is characterized by doubling. A few doublings lead to enormous numbers. With a large population base to start with in 1930, the growth between 1930 and 1938 would be great.
c) Overgrazing, death of plants, destruction of habitats, accumulation of wastes.
d) Overgrazing resulted in the death of plants and insufficient food. Weakened by a lack of food, the reindeer were prey to disease, and the reproductive rate could have declined drastically.
e) The population doubled in 1912 (1 year), 1915 (3 years), 1920 (5 years),
1930 (10 years), 1934 (4 years), 1937 (3 years). Doubling time between 1911 and 1938 became longer until 1930 and then shorter.
f) The population might die out because it is too small to recover, or it may slow the increase. Rationales will vary.
g) The population crested after 1938.
h) Natural controls take effect and can have drastic results, such as the total population dying out. Predators and hunters might have controlled the population, preventing exponential growth and the destruction of the environment, thus maintaining the carrying capacity of the environment.

Teaching
Tip Graph paper is available as Blackline Master Ecology 4.2: Graph of Human Population Growth.

Assessment Opportunity 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.

Part B: Human Population

Plot Date on y-axis and Human population (millions) on x-axis. Title of graph is Human Population Growth.

2. a) 1660 years
b) Decreasing
c) The human population is growing exponentially (very rapidly).
3. a) About 7000 million

5. a) Both show exponential growth curves.
b) Students may suggest some of the following factors: food, crop land, grazing land, forests, water, air.
c) Earth is a finite environment, like an island in space. Yes, Earth has a carrying capacity because it has finite resources.
d) The human population may decrease because of starvation or disease.
e) Student answers will vary. Some suggested methods include: birth control, abortion, infanticide, restriction on the number of children parents may have.
f) Answers may include: immigration, increasing water and air pollution, decreasing groundwater, increased soil erosion, decreased soil nutrients, loss of wildlife and wildlife habitat.
g) Factors that the students may consider include: water, living space, food supply, quality of life, justice.