A classic case study of how two populations interact comes from the snowshoe hare and its predator, the Canada lynx, in the forests of northern Canada. The Hudson's Bay Company kept records of the number of pelts sold by trappers for about a century, and these show that both populations rise and fall in a regular cycle of roughly 10 years.
1. With plenty of food, the hare population grows.
2. More hares mean more food for lynx, so more lynx survive and breed and the lynx population rises.
3. More lynx eat more hares, and the hares also run short of food (twigs and shoots), so the hare population falls.
4. With fewer hares, lynx starve or fail to breed, so the lynx population falls.
5. With fewer predators and recovering vegetation, the hare population rises again.The peak in lynx numbers comes a short time after the peak in hare numbers. This time lag occurs because it takes time for extra food to be turned into more surviving young predators.Field experiments later showed that predation is not the only cause. When hares were given extra food and also protected from predators by fencing, their numbers rose far more than when either factor was changed alone. So the cycle is driven by predation and food supply acting together.The data also have limitations: pelt numbers are only an estimate of population size, because they depend on how hard trappers worked each year.
1. With plenty of food, the hare population grows.
2. More hares mean more food for lynx, so more lynx survive and breed and the lynx population rises.
3. More lynx eat more hares, and the hares also run short of food (twigs and shoots), so the hare population falls.
4. With fewer hares, lynx starve or fail to breed, so the lynx population falls.
5. With fewer predators and recovering vegetation, the hare population rises again.The peak in lynx numbers comes a short time after the peak in hare numbers. This time lag occurs because it takes time for extra food to be turned into more surviving young predators.Field experiments later showed that predation is not the only cause. When hares were given extra food and also protected from predators by fencing, their numbers rose far more than when either factor was changed alone. So the cycle is driven by predation and food supply acting together.The data also have limitations: pelt numbers are only an estimate of population size, because they depend on how hard trappers worked each year.