Deterministic models of living and fossil populations of animals

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Abstract
The factors influencing the size-frequency distribution of living and dead populations of organisms are discussed. They include kind of recruitment (even recruitment, a broad wave of recruitment, a sharp wave of recruitment, and two waves of recruitment during the year); growth-rate (linear, high-to-low as in many invertebrates, and high-to-zero as in vertebrates) ; different coefficients of variation in the growth-rate; mortality rate (constant, increasing, and decreasing); and seasonal cessation of growth, with or without increased mortality. Forty-two steady-state experiments using different combinations and permutations of these variables have been run in a computer and the results expressed as size-frequency graphs of the living and resulting dead populations. The graphs are intended to be used as an aid to the interpretation of size-frequency in living and fossil populations of animals. It is shown that the growth-rate and the mortality rate are the major factors influencing the primary shape of the size-frequency distribution in living and dead populations. Secondary peaks may be developed as a consequence of seasonal recruitment accompanied by seasonal cessation of growth, with or without increased mortality. The difficulties of interpreting mass mortality in fossil populations are discussed.

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