The model

This is a spatial predator-prey model from population ecology. The prey are blue, and the predators are yellow. The prey and predators each reproduce; prey reproduce and die at certain intrinsic rates. Predators consume energy at a fixed rate over time; if their internal energy level becomes too low, they die. Predators' energy levels increase when they consume prey. If a predator's energy level becomes high enough, it has the opportunity to reproduce (although it may continue to spend effort foraging for more prey, rather than reproducing).

The Controls

See the parent web page for general controls.

Controls specific to this particular applet are:

• Prey density: a number indicating what percentage of sites will contain prey when the simulation is initialized. Either press "enter" after typing a number, or press the "Place prey" button to reinitialize the prey.
• Predator density: same as "Prey density" described just above, but for predators.
• Prey dispersal radius: when a prey reproduces, its offspring is dropped within the local neighborhood. This parameter describes the "radius" of that square neighborhood. E.g. if the radius is 2, offspring will be dropped within +/- 2 units of the parent in both the x and y directions. So with a radius of r, offspring will be dropped within a (2r+1)x(2r+1) block of sites. Another option is "Global", meaning prey offspring will be dropped on a site chosen at random from within the entire landscape. Finally, "von Neumann" means offspring are dropped in only the four adjacent sites (i.e. not on the diagonally adjacent sites).
• Predator dispersal radius: same as "Prey dispersal radius", but for predators.
• Prey forage radius: when predators search for prey to eat, they randomly choose a site within the local neighborhood; if there are prey there, they consume the prey (but the predator then remains in its original location). This parameter describes the size of the foraging neighborhood, in a manner similar to the "prey dispersal radius".
• rate1: This describes the ratio of the rates of prey versus predators. E.g. if its value is 2.3, it means prey events happen 2.3 times as often as predator events.
• rate2: how much more likely predators are to forage instead of reproducing, when they have sufficient energy to reproduce. E.g. if its value is 2.7, predators with enough energy to reproduce will in fact be 2.7 times as likely to forage rather than reproduce.
• rate3: This parameter describes the ratio of prey birth/death rates. If its value is 1, then prey birth and death rates are equal. If it's 2.5, prey births happen 2.5 times as often as prey deaths, and so on.

Things To Try

• The most interesting thing to try with this model is to vary the radius of prey dispersal, predator dispersal, and predator foraging, to see how it affects the population dynamics.