A practical guide to ecological modelling – shape

## ===================================================================================
## A figure to derive the 1-D transport equation from Soetaert and Herman, 2009 (book)
## implemented by Karline Soetaert
## ===================================================================================
 library(shape)
 par(mar = c(1, 1, 1, 1))
 plot(0, type = "n", xlim = c(-1, 1), ylim = c(-0.6, 0.5), axes = FALSE,
      xlab = "", ylab = "")
 col <- grey(seq(0.2, 1, length.out = 100))
 col <- c(col, rev(col))
 cex <- 1.75
#
 filledcylinder (rx = 0.15, ry = 0.4, len = 1, col = col, lcol = "black",
  lwd = 1, lcolint = grey(0.25), lwdint = 1, ltyint = 3,
  topcol = grey(0.5), delt = 1.15)
#
 segments(-1, 0, -0.5, 0)
 segments(0.5, 0, 1, 0)
#
 Arrows(-0.8, 0, -0.5, 0, arr.type = "triangle",
   arr.length = 0.5, lwd = 5, arr.adj = 1)
 Arrows(0.5, 0, 0.8, 0, arr.type = "triangle",
   arr.length = 0.5, lwd = 3, arr.adj = 1)
#
 text(0.0, 0.5, expression(Delta~V), cex = cex*0.9)
 text(-0.5, 0.225, expression(A[x]), cex = cex)
 text(0.5, 0.225, expression(A[x+Delta~x]), cex = cex)
 text(-0.75, 0.065, expression(J[x]), cex = cex)
 text(0.85, 0.065, expression(J[x+Delta~x]), cex = cex)
#
 segments(-0.5, 0, -0.5, -0.5, lty = 3, col = grey(0.25))
 segments(0.5, 0, 0.5, -0.5, lty = 3, col = grey(0.25))
#
 text(-0.5, -0.55, expression(x), cex = cex)
 text(0.5, -0.55, expression(x+Delta~x), cex = cex)