Populations don't live in isolation. They interact with other species. This graph lets you explore the interaction between a predator and its prey. This could represent populations of foxes and rabbits, for example, or wolves and deer, or sharks and tuna, and so on. You can adjust initial parameters, explained below, and click the “Apply changes” button to see the resulting graph. You can also use the “Random values” button, which will assign random values to each parameter and draw the resulting graph. This simple model assumes that the only limitation on the prey population size is predation and that the predator population depends solely on the number of prey available.
The horizontal axis on the graph is the time axis and the vertical axis is the population size. Note that the scale on the vertical axis changes to match the calculated values. Pay close attention to the vertical scale when comparing graphs. The time axis does not represent any particular period of time. It has no units. The point here is to explore patterns of change over time, not to reresent specific time periods. The horizontal axis always represents the same amount of time, though, so you can compare patterns on different graphs against each other. The prey population is shown in red and the predator population is shown in blue.
Prey starting population and Predator starting population are the number of individuals in each population at the beginning.
Prey ideal growth rate is the rate of prey population increase in the absence of limiting factors, e.g. if there were no predators. The actual growth rate of the prey population will vary with changes in the predator population. The numbers are arbitrary, larger means faster growth rate.
Predator death rate is the rate at which the predator population will die off when there is no prey to feed on. The numbers are arbitrary. Larger numbers mean the predators die off more quickly.
Prey nutritional value indicates the degree to which eaten prey results in new predators. The numbers are arbitrary. Larger numbers mean more new predators result from the same amount of food.
Predator effectiveness represents the degree to which encounters result in the prey being eaten. (A fox doesn't eat a rabbit every time it encounters one.) The numbers are arbitrary.
Make sure the values you enter are within the indicated ranges.