Abstract
TThe machine described in this report was con-
structed at a time when analog computers were
becoming fashionable. I had hoped to use it in
a study of the complex changes in population
structure that accompany changes in the reproductive rates and mortality rates of different age
classes of populations of small mammals. It soon
became apparent that the machine was capable of
"solving" various kinds of problems put to it,
but that preparation and calibration of the machine
for each problem was too time-consuming to make
it useful for solving witlh dispatch a series of
problems. More important, it soonl became ap-
parent that for not a single species of wild mani-
nial were there adequate field data to feed into the
machine to enable it to analyze to the full limit
of its ability the population problems for which
it was designed. In the process of putting ques-
tions to the machine, however, the operator fre-
quently became aware of various aspects of the
problem that mnight otherwise have been over-
looked. To be sure, an astute mathematician could
have foreseen all of these possibilities and made
room for them in appropriate equations, but for
the ordinary mathematically impoverished field
biologist the machinie proved to be a valuable
intellectual crutch. It is also a stimulating teaching
device that gives one the intellectual and esthetic
satisfaction (and excitement) of being able to
watch a population responding to the various
aspects of reproduction and mortality that tend
to keep its numbers in equilibrium.
It should be pointed out that I have designed
the machine to function in the manner that I be-
lieve populations function in the wild. Conse-
(ue:ltly, it is nothinig more than a mechaniical ex
pression of my own notions about popu'ations and
as such is perfectly capable of reproducing over
and over all of the misconceptions of its designer.
THE MODEL
Essentially the model consists of a long in-
clined plane into which a large number of holes
has been drilled and down whiclh balls are per-
mitted to roll. It resembles a metamerically elon-
gated pinball machine (Figure 1). As long as it
remains on the surface, the ball represents a living
animiial; when it falls through a hole it represents
a dead animal. Balls that "survive" long enough
are lermitted to "reproduce," thereby contributing
to the maintenance of the population. Numerous
em)bellishments, however, are necessary before the
model becomes rewardingly analogous to a wild
population, and these will be described below.
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