Predators and prey

In a healthy, balanced ecosystem the numbers of predators and prey remain fairly constant. They can go up and down during each year but generally over the years, these increases and decreases remain fairly constant.

If numbers of either predators or prey increase or decrease it could be due to a change in the abiotic factors, like water or sunlight, or biotic factors, like a new predator or pathogen. This would result in a less healthy, unbalanced ecosystem.

Predator-prey cycles

The numbers of predators and prey for certain ecosystems such as the Canadian Lynx (wild cat) and hare have been recorded over many years and found to change in a regular cycle. A similar example is shown in the graph below and shows characteristic repeating patterns called predator-prey cycles.

Predator prey graph.  As the number of predators increases the number of prey descreases. As the number of predators decrease the number of prey increase.

The graph shows that there is almost always more prey than predators. It also shows the following patterns:

  1. The number of predators increases when there is more prey.
  2. The number of prey reduces when there are more predators.
  3. The number of predators reduces when there is less prey.