Predator and Prey
Run a simulated meadow of hares and lynx. Change birth and hunting rates and watch the two populations rise and fall on a live graph.
1 hare = 50 hares 1 lynx = 2 lynx
How to use it
Pick a scenario and press Play. Hares (green line, left scale) eat plants and have babies; lynx (red line, right scale) eat hares. Change a slider while it runs to see what happens, or press Reset to start again from the starting numbers. One year passes about every second.
Try predicting first: if lynx get better at hunting, will there be more lynx or fewer in the long run? (Surprise: often fewer hares, and about the same or fewer lynx.)
Why the numbers go round in cycles
When there are lots of hares, lynx find food easily, raise more kittens and their numbers climb. Soon the many lynx eat hares faster than hares can be born, so the hares crash. With little to eat, lynx starve or have no young, and their numbers fall a year or two later. With few lynx left, the hares recover, and the cycle starts again. The lynx peak always comes after the hare peak. If predators are too successful, they wipe out their own food and then die out too.
This is a classic real story from Canada. The Hudson's Bay Company kept records of snowshoe hare and Canada lynx furs bought from trappers for about a hundred years (roughly 1845 to 1935). Ecologists found the counts rose and fell about every 10 years, with lynx following hares. Fur counts depended on trapping too, and later field studies in the Yukon (such as at Kluane Lake) showed that food supply, predators and stress all play a part in the real hare cycle. The model here uses the Lotka–Volterra equations with a limit on how many hares the meadow can feed (8000), so it is a simplified picture, not a forecast.
- Read the graph: how many years between hare peaks? Does the lynx peak come before or after?
- What happens to the hares when there are no lynx at all? Why do they level off?
- Which scenario is best for the lynx in the long run, and why?
Free to use, no account needed. It runs in your browser: nothing you type, and no sound from your microphone, is sent to Fieldbook.
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