population simulations in R

Greetings all -

I'm in the process of fitting some population models and had a question
regarding the simulation process in R.  Below I've pasted a simple code for
logistic growth with some stochasticity in the growth rate parameter ("r" -
see the runif part of the code).  If you run continue to repeat this code
you get a similar, but distinct and unique population model (i.e., graph of
population versus time) each time.  What I'm figure out is how to automate
the process to do this say...10 times...and plot all ten simulations on one
graph.  I'm trying to use a matrix approach, and fill each element.
However, I'm having difficulties figuring things out.

I appreciate any assistance offered,

Peter


Code:


test.logistic<-function(alpha=0.01, r0=1.2, f=0.2, N0=80, t=100) {
r<-c(r0, numeric(t))
for (i in 1:t) r[i+1]<- {
runif(1,0.8,1.1)
}
N<-c(N0, numeric(t))
for (k in 1:t) N[k+1]<- {
(N[k]+r[i]*N[k]*(1-(N[k]*alpha))-f*N[k])
}
return(N)
}
Nts<-bevholt()
t<-100
plot(0:t, Nts, type="l")





--
Peter Houk, PhD
Chief Biologist
Pacific Marine Resources Institute
www.pacmares.com
www.micronesianfishing.com

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