A comparative study of models for predation and parasitism

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justification of its use, see ROYAMA 1970). It was found that, for an intuitively rea-
sonable magnitude for the factor a, the calculated value for h was ridiculously high.
When the factor a was so adjusted as to obtain a more reasonable value for h, then
such values of a were inexplicably low. My conclusion was therefore that the estima-
tion of h by observation was far lower than it actually was. This is perhaps because
what was recorded as searching time must have contained a high proportion that was
spent upon various activities other than pure searching, e.g. watching for enemies.
These activities must have occupied such short intervals that they were hardly separable
by direct observation.
Beside such difficulties in measuring each activity separately and accurately, there
are more profound ones which may not be solved technically. The first is the time
factor. In order to take a sufficiently reliable measurement, say, of the fluctuation in
numbers of an animal species from year to year, the life span of a single ecologist
may not be sufficiently long: perhaps he can study only some twenty generations of
a univoltine species.
From a mere accumulation of sampling data, he can draw
conclusions by guessing, not by induction. The second difficulty lies in differences
between natural and experimental situations. The development of comparative ethology
in the past decade shows that the behaviour of animals has so evolved that its biologi-
cal goal is attained by responding appropriately to a chain of stimuli provided in
the animals' natural environment (see e.g. TINBERGEN 1951; for more recent develop-
ment see HINDE 1966). We cannot be certain on the one hand, however, if some of
the necessary stimuli are lacking in an experimental set-up in which the animals
concerned may not behave in an intelligible manner. But, on the other hand, we may
not be able to know, without experimental studies, what stimuli are involved in the
animals' normal environment where evolution has taken place. Then we will not be
certain whether we can establish a fact from which to follow the formula of induction
laid out by the classical physics, or rather if a fact at hand is a meaningful one that
can be used to start the gradual process of induction.
These arguments may be metaphysical problems, but are sufficient to show that
the primitive stage we are in at the moment, as compared with physical sciences, is
perhaps due to the above-mentioned difficulties, which prevented us consciously or
subconsciously from developing the method of inference by induction, starting from
an elemental stage where a deterministic prediction would not have been hard to make.
For the time being, ecology will perhaps remain largely descriptive, even if we
cannot expect to develop a deterministic law governing the hunting behaviour of
animals directly from such enumerations. A theoretical study by models, i.e. infer-
ence by analogy, will not replace the tedious process of enumeration, but it will at
least partially help in the interpretation of observed facts. The method will be useful,
however, only provided that the models are appropriately constructed and used. The
idea is perhaps the same as that suggested by OPPENHEIMER (1956) to a group of
psychologists as 'pluralism' in the method.