f <- function(N,b=0.4,k1=800,d=0.03,k2=50,k=0) { return ((b*(1-N/k1)-d*(1+N/k2))*N - k) } curve(f(N),xname="N",from=0,to=350,lwd=2,col="red",ylab="f(x)") lines(c(0,400),c(0,0)) curve(f(N,k=10),xname="N",from=0,to=350,lwd=2,col="blue",add=TRUE) # now add more curves for larger values of k (killing)