library(deSolve)
## Warning: package 'deSolve' was built under R version 3.3.2
metopob <- function (t, y, parms) {
    f = y[1]
    with(as.list(parms), {
        dp = pi*(1-f)-pe*f
        return(list(dp))
    })
}

prms <- c(pi=0.15, pe=0.05)
Initial.f=c(0.01)

out.M <- data.frame(ode(y = Initial.f, parms = prms, times = 1:100, func = metopob))

plot(out.M[,2]~ out.M[,1], type = "l", ylim=c(0,1), ylab = "f", xlab = "tiempo")