The model

This is a spatial population ecology model, where the population experiences spatially correlated extinction or disturbance events. The population is green. Births and deaths happen in continuous time at fixed rates. When deaths occur, entire blocks of sites go extinct simultaneously.

A "time step" for this model is defined as every L*L/4 events, where L is the size of the lattice (120 by default here). Because it's a continuous-time asynchronous model, during a "time step" here, on average 1/4 of the sites are updated, but some sites may be updated multiple times within a single time step.

This implements the model described in my paper "Spatially Correlated Disturbances in a Locally Dispersing Population Model", Journal of Theoretical Biology 232 (1), 143--149 (2005).

The Controls

See the parent web page for general controls. But if you're too impatient to read the instructions, just note that you need to right-click on the menu-buttons to pop up their menus.

Controls specific to this particular applet are:

• Initial population density: a number indicating what percentage of sites will contain be occupied by the organism when the simulation is initialized. Either press "enter" after typing a number, or press the "Place population" button to reinitialize the population.
• Dispersal radius: when an individual 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).
• birth rate: This describes the rate at which individuals produce offspring. The per-site death rate is assumed to be 1, so this parameter is really the ratio of the birth/death rates.
• blocksize1 and blocksize2: these specify the size of blocks which disturb (i.e. kill) the populaiton. E.g. if the block sizes are 2 and 3, then 2x3 blocks and 3x2 blocks of disturbances will rain down on the landscape (with equal frequency), killing individuals in any sites within the block.