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PubMed1989

Lebensraum: paradoxically, population growth may eventually end wars.

Population growth may progressively reduce 1 of the motives for making war. Namely, population growth threatens shortages of resources, and especially land. Impending shortages cause a search for ways to mitigate the shortages. The discoveries eventually produce greater availability of resources than if population growth and pressure on resources had never occurred. The argument runs as follows: 1) Rhetoric about resources scarcity induced by population density has often contributed to international conflict, even if economics has not been the main motive in making war. 2) In the pre-modern era, war to obtain land and other resources may sometimes have been an economically sound policy. 3) Politicians and others in industrially developed nations believe resources may still be a casus belli. 4) Land and other productive resources are no longer worth acquiring at the cost of war.

Agriculture↗
PubMed2005

Circadian G2 arrest as related to circadian gating of cell population growth in Euglena.

Cell population growth is gated to occur in particular circadian phases, which has been known for over four decades in various organisms including cyanobacteria and human. However, little is known as to which cell cycle phases from G1 to M are primarily regulated by the circadian rhythm or when in a circadian cycle this primary regulation takes place. We report here that in the flagellate alga Euglena gracilis grown photoautotrophically, the circadian rhythm primarily prevented developmentally matured G2 cells from progressing to mitosis, such that cell population growth occurred only during subjective night. In addition, we found that the circadian rhythm also arrests G1-to-S and S-to-G2 transitions at particular circadian phases.

Animals↗
PubMed1981

Population growth rates decline in five provinces.

Natural population growth rates in Shandong, Zhejiang, Shaanxi, Jiangxi, and Henan provinces last year were much lower than the 1980 national average of less than 11/1000, according to provincial authorities. The population growth rate in Shandong province, which has 73 million people, dropped to 7.03/1000 last year, 3.76/1000 less than in 1979. Some 100,000 fewer babies were born in Zhejiang province last year, compared with the figure for 1979. That birth rate was the lowest achieved in the past 30 years. In Shaanxi province, the population growth rate in 1980 was 7.19/1000. More than 458,000 couples in the province who have 1 child have decided to bear no more children, the authorities said. The population growth rate in Jiangxi and Henan provinces fell from 13.74/1000 in 1979 to 9.11/1000 in 1980 and from 12.88/1000 in 1979 to 9.53/1000 last year. The decline of the population growth rate is attributed to late marriage, late childbearing, family planning education, and encouragement of 1-child families.

Asia↗
PubMedDate not supplied

Population growth through history and the escape from the Malthusian trap: a homeostatic simulation model.

"A Malthusian simulation model is proposed to describe the growth of human population from the Neolithic through the Industrial Revolution. The economy is composed of a subsistence sector and a capital-producing sector. Our model captures the 'incessant contest' between population growth and the means of subsistence. When the per capita agricultural output falls below a biological minimum, the growth rate of the population is subject, in a random fashion, to perturbations that can take on disastrous proportions." It is suggested that "the slow accumulation of capital (and the buildup of the population of the capital-producing sector) eventually enables the population to overcome the constraints of the hostile economic environment. Our simulations (complete with confidence intervals) yield numerically realistic estimates of the population that eventually escapes from the Malthusian menace and grows unhindered during the Industrial Revolution." (summary in FRE, ITA)

Conservation of Natural Resources↗
PubMed2006

The contributions of age and sex to variation in common tern population growth rate.

1. The decomposition of population growth rate into contributions from different demographic rates has many applications, ranging from evolutionary biology to conservation and management. Demographic rates with low variance may be pivotal for population persistence, but variable rates can have a dramatic influence on population growth rate. 2. In this study, the mean and variance in population growth rate (lambda) is decomposed into contributions from different ages and demographic rates using prospective and retrospective matrix analyses for male and female components of an increasing common tern (Sterna hirundo) population. 3. Three main results emerged: (1) subadult return was highly influential in prospective and retrospective analyses; (2) different age-classes made different contributions to variation in lambda: older age classes consistently produced offspring whereas young adults performed well only in high quality years; and (3) demographic rate covariation explained a significant proportion of variation in both sexes. A large contribution to lambda did not imply a large contribution to its variation. 4. This decomposition strengthens the argument that the relationship between variation in demographic rates and variation in lambda is complex. Understanding this relationship and its consequences for population persistence and evolutionary change demands closer examination of the lives, and deaths, of the individuals within populations within species.

Aging↗
PubMed2002

Demographic, mechanistic and density-dependent determinants of population growth rate: a case study in an avian predator.

Identifying the determinants of population growth rate is a central topic in population ecology. Three approaches (demographic, mechanistic and density-dependent) used historically to describe the determinants of population growth rate are here compared and combined for an avian predator, the barn owl (Tyto alba). The owl population remained approximately stable (r approximately 0) throughout the period from 1979 to 1991. There was no evidence of density dependence as assessed by goodness of fit to logistic population growth. The finite (lambda) and instantaneous (r) population growth rates were significantly positively related to food (field vole) availability. The demographic rates, annual adult mortality, juvenile mortality and annual fecundity were reported to be correlated with vole abundance. The best fit (R(2) = 0.82) numerical response of the owl population described a positive effect of food (field voles) and a negative additive effect of owl abundance on r. The numerical response of the barn owl population to food availability was estimated from both census and demographic data, with very similar results. Our analysis shows how the demographic and mechanistic determinants of population growth rate are linked; food availability determines demographic rates, and demographic rates determine population growth rate. The effects of food availability on population growth rate are modified by predator abundance.

Animals↗
PubMed1993

UNICEF policy and perspectives: child survival, population growth, environment and development.

UNLABELLED: Rapid population growth is clearly a major problem in the world today. But to argue, as some do, that attempts to reduce child mortality by such means as vaccination should be abandoned, as a means of reducing population growth, is a fallacy for the following reasons. (i) Reducing child mortality has only a small effect on the population growth rate. (ii) Increasing child survival leads to a reduction in the numbers of children conceived. (iii) POPULATION: land ratios are not the main source of environmental pressure. (iv) It is the affluence of developed countries which contributes mainly to the pressure on available resources. The policy of UNICEF is thus to improve maternal and child health, to support and extend family planning programmes, and to seek to reduce the prevalence of very early marriage and teenage pregnancy.

Child↗
PubMed2002

Population growth rates: issues and an application.

Current issues in population dynamics are discussed in the context of The Royal Society Discussion Meeting 'Population growth rate: determining factors and role in population regulation'. In particular, different views on the centrality of population growth rates to the study of population dynamics and the role of experiments and theory are explored. Major themes emerging include the role of modern statistical techniques in bringing together experimental and theoretical studies, the importance of long-term experimentation and the need for ecology to have model systems, and the value of population growth rate as a means of understanding and predicting population change. The last point is illustrated by the application of a recently introduced technique, integral projection modelling, to study the population growth rate of a monocarpic perennial plant, its elasticities to different life-history components and the evolution of an evolutionarily stable strategy size at flowering.

Biological Evolution↗
PubMed1997

A comparison of acute mortality and population growth rate as endpoints of toxicological effect.

The objective of this study was to determine how closely acute (72-hr) lethal concentration estimates developed from probit analysis compared to the demographic toxicological endpoints, net reproductive rate (Ro), the intrinsic rate of increase (rm), and realized fecundity (Ux), in terms of predicting effects of pesticides on populations. Lethal and sublethal effects of the insecticide imidacloprid on the arthropod Acyrthosiphon pisum Harris (pea aphid) were determined for populations exposed to foliar-sprayed broad bean Vicia faba L. (variety Banner). An examination of Ro indicated that sublethal effects were occurring that reduced reproduction. However, by looking at the mean number of offspring produced per surviving female and Ux, it was determined that the reduction in Ro was entirely due to acute mortality and a reduction in life span. Also, exposure to increasing concentrations of imidacloprid did not cause a shift in either the day of initial reproduction or the day of peak reproduction. Therefore, this pesticide caused no sublethal effects on reproduction and, as such, a lethal concentration estimate should have been a good predictor of effect at the population level. However, the 72-hr lethal concentration estimate was not a good predictor of effect of this pesticide on population growth. Populations exposed to the 72-hr LC60 were able to maintain rates of population increase (rm = 0.224) similar to those of the control (rm = 0.295). The data indicate that the reason for the discrepancy between acute lethal concentration estimates and population growth was that surviving individuals were able to sustain heightened rates of reproduction following acute exposure to imidacloprid. The ability of surviving individuals to maintain these high reproductive rates allowed them to compensate for losses and act as reservoirs for future reproduction. It is not possible, using acute mortality estimates alone, to predict this "reservoir effect," and therefore not possible to predict how a population's growth rate will respond or change based on this endpoint. Thus this would suggest that the assessment of a xenobiotic based solely on acute mortality estimates will lead to flawed conclusions about a population's exposure response.

Animals↗
PubMed1981

[Shaanxi population growth].

In 1980, the natural population growth rate in Shaanxi declined to 7.19/1000. This was the best result since the launching of planned parenthood work in the province. The annual population increase declined from 570,000 in the early 1970s to 200,000 in 1980. In Tongchuan and Xian Municipalities and Hanzhong Prefecture, the population growth rate declined to 6/1000 while the rate in Weinan and Shangluo Prefectures declined to 7/1000. The party and CYL members have actively responded to the calls of the party Central Committee and State Council to spontaneously promote late marriage and late childbearing. Some 458,000 couples in the province have taken out single-child certificates. In the countryside throughout Shaanxi, 7100 young couples have settled in households where there are only daughters.

Asia↗
PubMed1998

Population growth and air quality in California.

Demographers are often interested in the environmental impacts of population growth. I examine the impact of growth specifically on air quality in California. In recent decades, California has suffered from notoriously polluted air and has experienced rapid population growth. Despite the population growth, air quality actually has improved since the early 1980s due to aggressive regulatory efforts. Using data for 56 counties, I analyze the contribution of population growth to trends in atmospheric emissions of five regulated pollutants from 1980 to 1990, controlling for trends in per capita income and regulatory efforts. The analysis is disaggregated by source of emissions and demonstrates that population growth is strongly associated with some sources of emissions but not with others. Thus, the overall impact of population growth depends upon the composition of production and consumption activities in each county. I also explore whether the trend in number of households predicts better than the trend in number of persons, and whether the impact of population growth depends upon the age structure or source of growth (immigration or domestic increase). Generally, these alternative specifications of population do not improve the models of atmospheric emissions.

Air Pollution↗
PubMed2006

Population growth, human development, and deforestation in biodiversity hotspots.

Human population and development activities affect the rate of deforestation in biodiversity hotspots. We quantified the effect of human population growth and development on rates of deforestation and analyzed the relationship between these causal factors in the 1980s and 1990s. We compared the averages of population growth, human development index (HDI, which measures income, health, and education), and deforestation rate and computed correlations among these variables for countries that contain biodiversity hotspots. When population growth was high and HDI was low there was a high rate of deforestation, but when HDI was high, rate of deforestation was low, despite high population growth. The correlation among variables was significant for the 1990s but not for the 1980s. The relationship between population growth and HDI had a regional pattern that reflected the historical process of development. Based on the changes in HDI and deforestation rate over time, we identified two drivers of deforestation: policy choice and human-development constraints. Policy choices that disregard conservation may cause the loss of forests even in countries that are relatively developed. Lack of development in other countries, on the other hand, may increase the pressure on forests to meet the basic needs of the human population. Deforestation resulting from policy choices may be easier to fix than deforestation arising from human development constraints. To prevent deforestation in the countries that have such constraints, transfer of material and intellectual resources from developed countries may be needed. Popular interest in sustainable development in developed countries can facilitate the transfer of these resources.

Animals↗
PubMed1997

Population growth, poverty and health.

One of the most popular explanations for the many problems that face Africa is population growth. Africa's population has doubled since 1960. Africa has the highest fertility rate in the world and the rate of population growth is higher than in any other region. At the same time, Africa faces a social and economic situation that is viewed by many as alarming. Among the problems that devastate Africa is that of persistent poor health. Africa has lower life expectancy, higher mortality rates and is affected by more disease and illness conditions than any other region. Focusing on sub-Saharan Africa, this paper examines the relationship between population growth, poverty and poor health. While most analyses have focused on population growth as an original cause of poverty and underdevelopment, this paper argues that while both population growth and poor health play a significant role in exacerbating the problem of poverty, they are themselves primary consequences of poverty rather than its cause.

Adolescent↗
PubMed2006

Molecular-level variation affects population growth in a butterfly metapopulation.

The dynamics of natural populations are thought to be dominated by demographic and environmental processes with little influence of intraspecific genetic variation and natural selection, apart from inbreeding depression possibly reducing population growth in small populations. Here we analyse hundreds of well-characterised local populations in a large metapopulation of the Glanville fritillary butterfly (Melitaea cinxia), which persists in a balance between stochastic local extinctions and recolonisations in a network of 4,000 discrete habitat patches. We show that the allelic composition of the glycolytic enzyme phosphoglucose isomerase (Pgi) has a significant effect on the growth of local populations, consistent with previously reported effects of allelic variation on flight metabolic performance and fecundity in the Glanville fritillary and Colias butterflies. The strength and the sign of the molecular effect on population growth are sensitive to the ecological context (the area and spatial connectivity of the habitat patches), which affects genotype-specific gene flow and the influence of migration on the dynamics of local populations. The biological significance of the results for Pgi is underscored by lack of any association between population growth and allelic variation at six other loci typed in the same material. In demonstrating, to our knowledge for the first time, that molecular variation in a candidate gene affects population growth, this study challenges the perception that differential performance of individual genotypes, leading to differential fitness, is irrelevant to population dynamics. These results also demonstrate that the spatial configuration of habitat and spatial dynamics of populations contribute to maintenance of Pgi polymorphism in this species.

Alleles↗
PubMed1974

Competition: a theory based on realistic, general equations of population growth.

Realistic equations of population growth, separately representing scarcity of renewed material resources and scarcity of fixed resources related to space, show the differential imnpact of these two factors on comnpetitive coexistence. The equations suggest a general theory of competition coverinlg any number or kinid of resolurces, consumers. and intraspecific and interspecific interactions.

Models, Biological↗
PubMed1985

On the optimum theoretical rate of population growth.

"The paper seeks intuitively-satisfying models of optimum population growth. The authors build upon Phelps's model of endogenous technical progress plus the Steinmann-Simon extension, which imply that the per-person consumption growth rate depends positively and linearly upon the population growth rate, without bound.... They suggest that the consumption rate ultimately turns downwards as population growth increases because of decreasing adoption of available technology as labor cheapens relative to capital, and as high population growth overtaxes people's will and ability to respond. Including a convex-downward function in the model yields sensible results." (summary in GER)

Demography↗