Dear R-users,

   I am currently modifying a previously developed predator prey model and
was curious if there was a way to add in a disturbance to the model (let's
say at time t=100).  The disturbance can be the introduction of 40 prey
(N=40) and 10 predators (Pred = 10).  I would like to see my model go from a
state of equilibrium (up to t = 99), show this disturbance (at t = 100) and
then slowly work its way back to equilibrium.  Does anybody know if this
could be done?


LVmod0D <- function(Time, State, Pars) {

with(as.list(c(State, Pars)), {

IngestPred <- rI * N * Pred

GrowthN <- rG * N * (1 - N/K)

MortPred <- rM * Pred



dN <- GrowthN - IngestPred

dPred <- IngestPred * AE - MortPred



return(list(c(dN, dPred)))

})

}



pars <- c(rI = 0.1, rG = 0.9, rM = 0.8, AE = 0.9, K = 20)

yini <- c(N = 20, Pred = 20)

times <- seq(0, 200, by = 1)

y(time=100)<-c(N=10, Pred=5)

print(system.time)

zout <- as.data.frame(lsoda(yini, y(time=100), times, LVmod0D, pars))

plot(zout[,1],zout[,2], type="l",col="black", ylim=range(0,25),
xlab="time",ylab="population")

points(zout[,1],zout[,3],type="l",col="red")

title(main="prey (black) predator (red)")



Thanks much for your help!

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