Fig_12

#---- Huffaker 2 naranjas
# fig_12

# variables
N1 <- numeric()  # naranja 1
P1 <- numeric()
N2 <- numeric()  # naranja 2
P2 <- numeric()

# coeficientes
lambda <- 1.4    # tasa crecimiento
c <- 3           # huevos parásito
a <- 0.01         # eficacia parásito
m <- 0.05         # fracción emigrante

# condiciones simulación
ngen <- 2000      # generaciones
N1[1] <- 30      # N inicial
N2[1] <- 0
P1[1] <- 50      # P inicial
P2[1] <- 0

# simulación
for (t in 1:ngen) {
  # en la naranja 1
  f1 <- exp(-a * P1[t])
  N1[t + 1] <- lambda * N1[t] * f1 * (1 - m) + m*N2[t]
  P1[t + 1] <- lambda * c * N1[t] * (1 - f1) * (1 - m) - m*(P1[t] - P2[t])
  # en la naranja 2
  f2 <- exp(-a * P2[t])
  N2[t + 1] <- lambda * N2[t] * f2 * (1 - m) + m*N1[t]
  P2[t + 1] <- lambda * c * N2[t] * (1 - f2) * (1 - m) - m*(P2[t] - P1[t])
}

# gráfico (dos en la misma figura)
pdf("fig_12.pdf", width = 7, height = 6)
par(pty = "s",
    bty = "n",
    mar = c(5, 2, 1, 1),
    xaxs = "i",
    yaxs = "i",
    las = 1)
plot(N1, P1,
    type = "b",
    lty = 1,
    cex = 0.8,
    pch = 16,
    col = "royalblue",
    xlim = c(0, 120),
    ylim = c(0, 300),
    xlab = "N",
    ylab = "P")
lines(N2, P2,
    type = "b",
    lty = 2,
    cex = 0.8,
    pch = 21,
    col = "coral")
legend("topright",
    c("naranja 1", "naranja 2"),
    lty = c(1, 2),
    cex = 1,
    pch = c(16, 21),
    col = c("royalblue", "coral"),
    bty = "n")
dev.off()