- This week Eric Klopfer
is guest chef here in the Kitchen. He offers a follow-up report on a three-species
ecological model for biocontrol originally investigated with the CAM8 mixmaster
Whereas the CAM8 version used density-dependent state values for the
predator and two types of prey, Eric's new implementation involves only
presence or absence of each type within a cell. Nevertheless the observed
behavior is qualitatively the same, confirming in this instance that the
two modeling approaches are essantially equivalent. [Technical note: the
two animated gif sequences on this page fill nearly 1Mb, so
those with slow connections should look over the text until the data is
downloaded to a local cache, after which they will loop in real time.]
Apparent Competition as a Result of Spatial Interactions
These are simulations of a presence-absence cellular automaton model for
a single predator and two prey. One prey (blue) is a pest while the other (green) is not.
The pest is characterized by its higher birth rate. The predator (red) is present
in order to control the pest, and thus attacks it more aggressivlely than the non-pest,
which does not always need to be present.
Three Species Dynamics
When the non-pest species is present it can provide access to the isolated
pockets of pests that are not accessible in the two species model. While the
two prey do not compete directly, and coexist in the absence of the predator,
when the predator is present it now drives the pest extinct. The non-pest can
then persist with the predator, and this two species system is stable to reintroduction
of the pest (i.e. the pest is again eliminated if it is reintroduced).