1. Rabbits and Lynx in Northern Canada
The daily life of the lynx is closely tied to the snowshoe rabbit. The lynx has a huge
appetite for these rabbits, and its body is particularly well suited to hunting them. In
summer, the lynx often feeds on mice or ground squirrels, but its mind seems to generally
fill with visions of Peter Lepus, and its imagination travels beyond a rabbit dinner only
with difficulty. This would be all very well, except that through the ages things have
come to pass that the lynx cannot do very well without the rabbits.
Since rabbits do not have Planned Parenthood, their numbers depend wholly on natural
laws. For a period of years the rabbit population grows rapidly. For the lynx, this makes a
very rosy world. Its food supply increases by leaps and bounds; the lynx flourish and
baby lynx abound. A day comes when there are hundred of rabbits per square mile and a
large lynx population. The woods are filled with life and activity. The size and
concentration of the rabbit population, however, jeopardizes every rabbit, for now any
disease can spread rapidly. And that is what generally happens in Northern Canada unless
food scarcity strikes first. Great numbers of rabbits die of disease. In a year or two, the
lynx find the woods empty. Starvation is now a problem. The lynx roam the woods,
capturing what they can. Old hunting grounds are deserted; where there were dozens of
rabbits there may now be none. New habitats are explored and hunting new prey takes
place. Lynx become thin and fail to reproduce, and in a year or two are scarce or absent
over wide areas.
Little by little, first slowly, then more rapidly, the rabbits come back and grow in
numbers again. Lynx recover, too, and become more plentiful. The pattern of the rabbit
and lynx cycle continues.
1. Draw the Causal Loop
2. Draw a stock flow diagram showing the rabbit and lynx cycle. (Clue: the total
number of lynx depends on how many lynx are born and many lynx die. The number
of lynx that die depends on how much food they have. The total number of rabbits
depends on the number of rabbits that are born and the number of rabbits that die. The
number of rabbits that die depends on the number of lynx as well as the amount of
food available and disease. Food and disease depend on the density of the rabbit
population.).
3. Construct the DYNAMO Model