Antler Points

The figure nearby is a phase plane, a diagram very useful for understanding a deer herd. It is based on a forgotten or not-emphasized premise, one that is emphasized by R* Deer-size of the deer population in an area is more influenced by the previous population than by any factor of the environment. This rule, like all rules, is limited. There's a lot of truth in it, though not all. The point of the spiraling diagram (called a phase plane) is that the deer harvest in any year is strongly related to past harvests. If you over-harvest this year, your hunt club will probably take fewer deer next year. The graph says the same thing.

Starting with 1990 data (when there was no previous data), we plot the first point, 30 deer. We take 45 the next year and it turns out that this may be too many so the next year (1992) we only take 25. We continue in this way, eventually achieving a constant harvest of abut 30. This is a representative diagram. When animal populations reach near the center (about 30) they may jump around a little, even a great amount if a fire, storm or other change occurs-then it will "circle", arriving at a new point of stability.

Thinking of a population circling, about achieving its point of stability may be a useful idea. A very unstable region (farming, changing land use, floods, etc.) will rarely have a smooth phase plane as shown here. Another picture of great value is to plot the harvest two years before. They often are even more valuable than using a single year.

In a future article , we'll look at this diagram sideways. This picture of the phase plane is a view as if looking down on a coil, a wire spring, of deer data.

This Web site is maintained by R. H. Giles, Jr.
Last revision January 17, 2000.