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On the Reproduction of Organisms with overlapping Generations

Published online by Cambridge University Press:  10 July 2009

W. R. Thompson
W. R. Thompson
Affiliation:
Imperial Institute of Entomology.
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Extract

In the great majority of organisms, the reproducing individual does not engender all of its progeny simultaneously. Between the beginning and the end of the reproductive period there is usually a certain interval of time, during which the production of offspring continues in a manner depending, on the one hand, upon the specific characteristics of the organism, and on the other, upon the conditions under which it lives. From this simple fact follow some interesting consequences.

If the successive generations are separated by a long interval of time and conditions during this interval are of such a nature that the organism is inactive and in the condition of obligatory dormancy, known as diapause, then, in spite of the increase of the population, the generations will remain separate and distinct, and a comparison of the total populations in the successive reproductive periods will enable us to determine the rate of increase.

On the other hand, if the interval between generations is short and favourable to activity and the organism does not pass through a period of obligatory dormancy at this time, then, as the species increases, the successive generations will come to overlap, and the amount of overlapping will increase progressively as time goes on.

This is primarily due to the fact that when there is reproduction over a period of time-intervals, in a typical individual of the species, and conditions remain constant then the number of time-intervals during which births occur will increase from generation to generation.

Type
Original Articles
Information
Bulletin of Entomological Research , Volume 22 , Issue 1 , April 1931 , pp. 147 - 172
Copyright
Copyright © Cambridge University Press 1931

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References

* While this paper is passing through the press I have learnt with the greatest regret of the death of Mr. Soper.

* Instead of saying “ per day,” we could say “ per interval of time,” including a period either less than or greater than a day ; the course of the argument would be the same.

* The process given here is, as a matter of fact, simply a special application of Mr. Soper's method of Formulation by Objective Symbols, which he has discussed in detail in a special work (Frequency Arrays, Camb. Univ. Press, 1922).

* We say that Gr is negligible when r = ∞, not because G < 1, but because we do not concern ourselves with the exact enumeration of events at infinite time.

† It would perhaps have accorded better with our common conceptions had populations been put at instants and births in intervening intervals of time.