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At least 19 recordsLinked to original sources
PubMed1985

Generalized stable population theory.

In generalizing stable population theory we give sufficient, then necessary conditions under which a population subject to time dependent vital rates reaches an asymptotic stable exponential equilibrium (as if mortality and fertility were constant). If chi 0 (t) is the positive solution of the characteristic equation associated with the linear birth process at time t, then rapid convergence of chi 0 (t) to chi 0 and convergence of mortality rates produce a stable exponential equilibrium with asymptotic growth rate chi 0-1. Convergence of chi 0 (t) to chi 0 and convergence of mortality rates are necessary. Therefore the two sets of conditions are very close. Various implications of these results are discussed and a conjecture is made in the continuous case.

Age Factors↗
PubMed2001

Obesity and body mass index in Spain: the 'single population' theory revisited.

OBJECTIVE: The 'single population' theory suggests that the distribution of body mass index (BMI) moves up and down as a whole. We test directly whether this theory is valid among the adult population within one country over time, by examining the association between median BMI and the prevalence of obesity in the adult population of Spain's 17 regions between 1987 and 1993. DESIGN AND SETTING: Ecological study using data from two national health surveys. SUBJECTS AND INTERVENTIONS: Self-reported weight and height for persons aged 20-64 y were drawn from representative Spanish-population samples from two similar National Health Surveys carried out in 1987 (n = 20 705) and 1993 (n = 15 490). MAIN OUTCOME MEASURES: Correlation and linear regression between the difference in median BMI and the difference in the prevalence of obesity (BMI > or = 30 kg/m(2)) between 1987 and 1993. RESULTS: Between 1987 and 1993 the change in median BMI was in general strongly correlated with the change in the prevalence of obesity (r = 0.85; P < 0.001). The correlation is greater in women, persons over 45 y, and those with lower educational levels. Between 1987 and 1993 each unit of increase in median BMI is associated with an absolute increase of 5.1% (95% CI 3.3-6.8%) in the prevalence of obesity. CONCLUSIONS: The single population hypothesis holds true among the adult population within a whole country over time. This could be useful for monitoring and understanding the prevalence of obesity within a population.

Adult↗
PubMed2004

Stochastic population theory faces reality in the laboratory.

Understanding the factors that affect most severely the extinction risk of populations is crucial for maintaining biodiversity. An important general pattern derived from stochastic population theory is that time to extinction should decrease with increasing environmental stochasticity. Drake and Lodge recently provided one of the first pieces of experimental support for this simple prediction by artificially manipulating the dynamics of populations of Daphnia. A future challenge will be to include both demographic stochasticity and environmental stochasticity in such studies.

Journal Article↗
PubMed1989

Diminishing returns and Malthus's first essay on population: theory and application.

"This paper argues that Malthus's famous geometrical and arithmetical ratios do not necessarily imply diminishing returns. That average product would not necessarily fall with increased population density is immaterial to the polemical purpose of the Essay on Population which is satisfied by demonstrating the necessity for a reduction of the population growth below its maximum potential. But I do not deny the presence of the diminishing returns principle in the first Essay. Indeed, here is found the origin of Malthus's later land-scarcity based growth model involving a declining path of real wages in consequence of a decelerating rate of growth of labour demand." The author also considers Malthus's analysis of the situation in Britain in 1798. (SUMMARY IN FRE)

Agriculture↗
PubMed1985

[Overpopulation--a cause of war? Notes on the population theory of Thomas Robert Malthus].

The relationship between Malthusian pressures and the frequency of wars in seventeenth- and eighteenth-century Europe is examined. The author concludes that Europe at that time could easily support its population above subsistence level. "It was the political regime of absolutism which established mechanisms of income distribution that impoverished a large fraction of the society. The numerous barriers to market entry of the guild system and primogeniture as the predominant bequest rule among nobles left many young men, commoners and nobles alike, no choice but to join the army. In order to reduce the number of expensive mercenaries it was then individually rational for the princes to more or less continuously participate in militant conflicts." (summary in ENG, FRE)

Conservation of Natural Resources↗