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Biomedical subjects

L Demetrius

Publications and source records attributed to L Demetrius.

7 recordsLinked to original sources
PubMed1979

Relations between demographic parameters.

The mean life-expectancy e describes the average prospective life-time of an individual aged zero. This parameter can be explicitly described in terms of the survivorship distribution of the population. The Malthusian parameter r represents the asymptotic growth rate of a population. This parameter can be implicitly expressed in terms of the net-maternity distribution. The parameters e and r incompletely incorporate the age-specific fertility and mortality pattern of a population; distinct populations may have the same growth rate but different net-maternity functions; distinct populations may be characterized by the same mean life expectation but may have different survivorship distributions. This article analyzes a class of parameters called the entropy of a population (Demetrius, 1974a) which distinguishes between net-maternity functions with the same growth rate and also mortality distributions with the same mean life expectation. This class of parameters measures the convexity of the fertility and mortality distributions. This paper analyzes the relations between the entropy parameter and the standard demographic parameters.

Demography↗
PubMed1977

Measures of fitness and demographic stability.

The concepts of entropy and reproductive potential of a genotype were introduced in a previous paper [Demetrius, L. (1974) Proc. Natl. Acad. Sci. USA 71, 4645-4647] and an analoge of the fundamental theorem of natural selection was derived. This paper relates to entropy of a population with the rate of convergence of the population to the stable age distribution. I show that (i) at maximal entropy, no oscillatory components exist and the birth sequence is unaffected by perturbations in the stable age distribution; and (ii) at zero entropy, oscillatory components occur and increase as rapidly as the real exponential component in the birth sequence. These results have implications towards (i) the relation between population fitness and adaptedness, (ii) modes of selection and the evolution of reproductive strategies, and (iii) the evolution of senescence.

Aging↗
PubMed1975

Natural selection and age-structured populations.

This paper studies the properties of a new class of demographic parameters for age-structured populations and analyzes the effect of natural selection on these parameters. Two new demographic variables are introduced: the entropy of a population and the reproductive potential. The entropy of a population measures the variability of the contribution of the different age classes to the stationary population. The reproductive potential measures the mean of the contribution of the different age classes to the Malthusian parameter. The Malthusian parameter is precisely the difference between the entropy and the reproductive potential. The effect of these demographic variables on changes in gene frequency is discussed. The concept of entropy of a genotype is introduced and it is shown that in a random mating population in Hardy-Weinberg equilibrium and under slow selection, the rate of change of entropy is equal to the genetic variance in entropy minus the covariance in entropy and reproductive potential. This result is an information theoretic analog of Fisher's fundamental theorem of natural selection.

Age Factors↗