ZOO 4400/5400 Population Ecology

Intraspecific competiton -- discrete logistic equation
low r slightly oscillating approach to K case Eqn 15.1

Embedded QuickTime Movie (from Mathematica notebook r1Movie.nb)

Click on the image below to start the "movie". A control bar will appear below the graph; the various buttons will allow you to stop and start it.

Fig. 1. One-dimensional "map" of the discrete logistic (Eqn 15.1, above) with r = 1.5 and K = 1,000. Note that the population converges very quickly on K. We start with an N(t) value on the X-axis, move up to the "map" (red line) to get an N(t+x) value and then take the corresponding Y-value by going over to the 1:1 black line, then again move to the red line. Tracing the map is therefore a process of going back and forth from the red map line to the black N(t+x) = N(t) 1:1 line (like a stair step -- "up, over, up, over"). Following the map this way gives us the successive population sizes over time. Note that the trajectory moves toward the stable equilibrium point (at K = 1,000).  The last few frames involve changes so small they don't show up onscreen.

The low r value here is what permits the convergence on K. Fig. 2. Static view of the trajectory toward the stable equilibrium at K = 1,000 from a starting N0 of 120.
Note the stair step ascent from the starting value to K.  The very slight oscillations are shown by the lines spiralling inward around K.