Case Study: Investigating a Predator-Prey Relationship
In this case study you will investigate one of the most famous sets of data ever collected on a predator-prey relationship. The data comes from records kept by the Hudson’s Bay Company over many years.
Lynx, a cat of the boreal forest, prey on snowshore hare. In some areas, hare provide over 70% of the lynx diet. As a result, the population growth curve of the lynx should show a relationship to that of the hare.
The data on this relationship are listed in the following table. Study them carefully as you answer the questions.
Population Numbers of Hare and Lynx by Year
Year / Hare Numbers x 1000(blue) / Lynx Numbers x 1000
(red)
1900 / 30.0 / 4.0
1901 / 47.2 / 6.1
1902 / 70.2 / 9.8
1903 / 77.4 / 35.2
1904 / 36.3 / 59.4
1905 / 20.6 / 41.7
1906 / 18.1 / 19.0
1907 / 21.4 / 13.0
1908 / 22.0 / 8.3
1909 / 25.4 / 9.1
1910 / 27.1 / 7.4
1911 / 40.3 / 8.0
1912 / 57.0 / 12.3
1913 / 76.6 / 19.5
1914 / 52.3 / 45.7
1915 / 19.5 / 51.1
1916 / 11.2 / 29.7
1917 / 7.6 / 15.8
1918 / 14.6 / 9.7
1919 / 16.2 / 10.1
1920 / 24.7 / 8.6
Questions
1. On the graph paper provided, use one colour of pencil to graph the number of hares trapped each year between 1900 and 1920. Using another colour, graph the number of lynx trapped.
2. a) These population growth curves are said to fluctuate. Look up fluctuate in the dictionary. What does it mean?
b) How many years are there in one fluctuating cycle of the hare population?
3. a) Why does the hare population fluctuate?
b) Why does the lynx population fluctuate?
c) How do the two populations affect each other?
4. As the number of hares decreases, what do you think happens to the population of grass and seeds that the hares eat? Why do you think this is?
5. In general, are there more lynx or more hares? Why do you think this is?
6. Look at 1903 and 1904. Think about what is happening to the hares at this time. Is the presence of more lynx helping the hares or hurting them? Why?
7. We say that a good predator-prey relationship keeps the two populations “in balance”. What is meant by this?
8. a) Lynx skins are quite valuable today. What would happen if trapping regulations were abolished and all the lynx in an area were killed?
b) Are trappers likely to kill all the lynx in an area, even if regulations were abolished?