Demographic Cycles Research Articles

Timing of childbirth, capital accumulation, and economic welfare

This paper examines the effect of the timing of childbirth on capital accumulation and welfare in a simple overlapping generations model, where each agent lives for four periods and works for two periods. We show that delayed childbearing not only reduces population, but also generates fluctuations in the age composition of workers in the labor force. This causes the aggregate saving rate to fluctuate, which leads to cycles in the capital-labor ratio. When all agents delay childbearing, we analytically show that both the capital-labor ratio and the welfare of all agents can fall in the long run, despite the population decline. When a fraction of agents delay childbearing, it has differential welfare effects on agents depending on their positions in the demographic cycles. The effects of lower lifetime fertility and technological progress are also examined.

PAYG Pensions and Economic Cycles

In this article we compare the dynamics and long-run outcomes of an overlapping generations closed economy under exogenous and endogenous fertility. Individuals have myopic foresight, and pay-as-you-go (PAYG) public pensions exist. Although large PAYG transfers may cause endogenous fluctuations in both contexts, cyclical instability and deterministic chaos more likely occur when fertility is an economic decision variable. We find that the existence of endogenous fertility and PAYG pensions can explain the occurrence of demographic oscillations that mimic the baby boom and baby bust, in contrast with the unrealistic case of constant population, and also economic cycles. We also show that an increase in the social security contribution rate under endogenous fertility, often advocated as a remedy against the crisis of public pension budgets, may prolong both the phases and size of demographic (economic) cycles around a lower (higher) long-run level of population growth (income per worker) than under exogenous fertility.

Different life-history trade-offs of twoDaphniaspecies (Cladocera, Crustacea) under natural conditions as the response to predation and competition

Daphnia longispina (O. F. Muller 1785) and Daphnia cucullata (G. O. Sars 1862), despite coexisting in similar densities in the lake, showed different demographic cycles. To search the causes of such variances between the two Daphnia , selected population parameters (density, body proportions, reproductive output) were correlated with the density of five dominant and potentially competitive species of Cladocera. The same parameters were estimated in relation to predation pressure of vertebrates (planktivorous fish) and invertebrates (Leptodora kindtii (Focke 1844)). The obtained results show that competition had no apparent impact on life-histories of Daphnia . Different strategies of the two Daphnia resulted from the uneven effect of invertebrate and vertebrate predators. D. longispina that was affected by planktivorous fish and Leptodora kindtii invested in reproduction and carried big egg-clutches. D. cucullata, which was insignificantly influenced by fish, displayed low reproductive output but changed their body proportions in the process of cyclomorphosis when occurring with L. kindtii . Other life-history trade-offs altered during the year, in accordance with the intensity of predation pressure.

Phase-dependent effect of conservation efforts in cyclically fluctuating populations of arctic fox ( Vulpes lagopus)

Predator populations with demographic cycles driven by multi-annual cycles of their key prey resource can be expected to be “cyclic phase sensitive” to management actions. We explored this by means of modelling in the case of the highly endangered Fennoscandian arctic fox population which is driven by 4-year population cycles in small rodent prey. By using a model in which the management action improved arctic fox vital rate through increased resource availability, we show that arctic fox population growth was most improved when management action was applied in the increase and decrease phase of the cycle. Except in the low phase of the cycle, the growth rate was more affected when the management action worked through improved reproduction than improved survival. There was a synergistic effect to be gained by performing management action during multiple phases during a demographic cycle. Thus we recommend that arctic fox conservation programs ought to be continuous in time, but with the highest intensities of management action in the phases of the cycle in which the target population is most prone to respond.

Challenges for a cross-disciplinary geoarchaeology: The intersection between environmental history and geomorphology

Geoarchaeology is a growing subfield of cross-disciplinary research at the intersection between geomorphology, environmental history, and archaeology. This prospective essay does not aim to analyze the nature or evolution of geoarachaeology, or to review available techniques and methods. Instead it addresses challenges. Exciting challenges confront geoarchaeology in the form of persistent problems that demand satisfactory solutions, despite improving skills and innovative technologies. Drawing from the full record of human history, a number of practical issues can be highlighted to explicate these challenges: (1) Open-air archaeological sites are the main object of study for the Early to Mid-Pleistocene, even though they represent open systems that raise fundamental questions about archaeo-taphonomic integrity. How were sites buried and then modified by selective preservation, horizontal or vertical disturbance, and the role of carnivores? Is it possible to determine the degree to which such sites accurately record prehistoric human behavior, prior to the Late Pleistocene when hearths and living structures lend better definition to occupation surfaces? Can non-primary open-air sites also shed light on human activities and environmental history? (2) Cave sites have long been favored by archaeologists because of the impression that they represent relatively complete and undisturbed archaeostratigraphic sequences. But serious problems also exist here in regard to the nature of accumulation and the sources of mineral and biogenic sediments in what were open systems, liable to disturbance, despite comparatively low-energy processes. (3) Less familiar are urban and other architectural sites, where processes of formation and degradation mimic natural sedimentation and erosion. Such a geoarchaeology can be highly informative for urban processes, demographic cycles, or the intersection between sites and their surrounding landscapes. (4) Spatial components of geoarchaeological research need more systematic consideration, for locational strategies and with an appreciation that site presence or absence allows a more dynamic modeling of settlement and procurement strategies. (5) Regional settlement expansion and contraction may also inform on mosaic evolution or Pleistocene dispersals, including the Out of Africa hypothesis. (5) Finally, multiple themes connected with environmental degradation during Holocene times may open new windows to examine specific problems by objective criteria, so contributing to a wider academic discourse about long-term trends, the interfingering of climatic and land-use factors in cause-and-effect dilemmas, or the construction of future scenarios in an era of accelerating planetary change. The focus of archaeology is shifting to later ranges of prehistory so that geoarchaeologists now have a mandate to engage more directly with urban, spatial, and degradation issues. This should be met with a broader and more inclusive agenda, one that optimizes on expertise with historical geomorphology and environmental history, but in collaboration with archaeologists and other social scientists. That would sustain a more prominent role for geoarchaeology in the university curriculum.

Stress and Demographic Decline: A Potential Effect Mediated by Impairment of Reproduction and Immune Function in Cyclic Vole Populations

The stress response is initially adaptive, operating to maintain homeostasis. However, chronic long-term exposure to stressors may have detrimental effects. We proposed that chronic stress may be a major factor in demographic vole cycles, inducing decline in high-density populations. We monitored four populations of the fossorial water vole Arvicola scherman, which undergo pluriannual demographic cycles in the Jura Mountains (France). Sampling was conducted during the high densities and the decline. We measured fecal corticosterone metabolites (FCMs) to assess stress levels and injected phytohemagglutinin to estimate the cell-mediated immune response. We demonstrated that stress levels increase between the high densities and the decline in most of the vole populations. At the individual level, FCM concentrations varied with reproductive status and body condition. During the outbreak, we observed significantly higher levels of FCM concentrations in nulliparous females than in females that had previously reproduced. Moreover, a significant negative correlation was observed between concentrations of FCMs and both immunocompetence and body condition during population decline. These results might reflect an impairment of the female reproductive capability in high densities and accelerated senescence affecting immune function during decline, both arising from chronic stress.

Regulation of vole populations by the nematode Trichuris arvicolae: insights from modelling

The goal of this study is to determine whether a parasitic nematode may regulate, or destabilise by inducing demographic cycles, its host populations. We explore three host–parasite systems through population dynamic models. The hosts considered are the fossorial water vole, Arvicola terrestris, the common vole Microtus arvalis and the bank vole Myodes (Clethrionomys) glareolus and the parasitic nematode is Trichuris arvicolae. Three differential equation-based mathematical models are developed including host immunity and the existence of trade-off between immunity and host survival. Using parameters estimated from field data and laboratory observations, all these models show that T. arvicolae can induce host population regulation but not demographic cycles. The regulation effect of the nematode is un-ambiguous for the water vole (reduction of 50.2% of the host population size), but less obvious for the common vole (5.9%) and even less for the bank vole (1.4%). Important biological parameters to be taken into account in such models are discussed. Experimental confirmation of the regulatory potential of the nematode and of the costs of mounting an immune response against this nematode are now required.

Comment on: Dynamical Feedbacks between Population Growth and Sociopolitical Instability in Agrarian States by Peter Turchin

Turchin’s article achieves significant progress in the modeling of demographic cycles as a basic feature of complex agrarian systems' dynamics. He suggests an extremely simple model accounting for an unusually high percentage of the political-demographic variation, including some features for which earlier models failed to account. Rather than modeling the recovery phase of the demographic cycle as starting immediately after the demographic collapse, which is not observed in reality, the recovery phases of Turchin’s model are, more accurately, separated from those of collapse by significant periods of internal warfare that blocks recovery growth. Such intercycles, systematically observed in the agrarian political-demographic dynamics, represent a problem that Turchin has managed to solve in a very elegant and compelling way.

Large-amplitude cycles of Daphnia and its algal prey in enriched environments

Ecological theory predicts that stable populations should yield to large-amplitude cycles in richer environments1,2,3. This does not occur in nature. The zooplankton Daphnia and its algal prey in lakes throughout the world illustrate the problem4,5,6. Experiments show that this system fits the theory's assumptions7,8,9, yet it is not destabilized by enrichment6. We have tested and rejected four of five proposed explanations10. Here, we investigate the fifth mechanism: inedible algae in nutrient-rich lakes suppress cycles by reducing nutrients available to edible algae. We found three novel results in nutrient-rich microcosms from which inedible algae were excluded. First, as predicted by theory, some Daphnia-edible algal systems now display large-amplitude predator-prey cycles. Second, in the same environment, other populations are stable, showing only small-amplitude demographic cycles. Stability is induced when Daphnia diverts energy from the immediate production of young. Third, the system exhibits coexisting attractors—a stable equilibrium and large-amplitude cycle. We describe a mechanism that flips the system between these two states.

Demographic transition, stagnation, and demoeconomic cycles in a model for the less developed economy

The paper considers a dynamic macroeconomic model for a developing economy. Population varies endogenously according to the theory of demographic transition. It is shown under which circumstances this economy converges either to a steady-state growth path or to a low-level equilibrium. The latter may be a Malthusian stationary steady-state or a limit cycle. Strong fluctuations in the demoeconomic variables, which can be observed for some developing countries, can be explained as endogenous oscillations. Positive exogenous shocks may cause an escape from the equilibrium trap and initiate a process of demographic transition if they are properly timed and of sufficient duration.

Demographic Cycle Effects on Migration Timing and the Delayed Mobility Phenomenon

This paper examines the effect of a cohort's size and position in the demographic cycle on the timing of migration during the young, labor force years. Previous literature has shown that demographic cycles are highly influential in determining the level of migration: migration propensities of young adults tend to be lower for large cohorts due to competitive labor markets and depressed job opportunities. This study argues that demographic cycles can also influence the timing of migration, and proposes a methodology that separates the examination of migration levels from that of migration timing. Analyses using Current Population Survey data show that members of small cohorts tend to move earlier on in their life cycle than members of large cohorts. Reconstructed age‐schedules of migration for large and small cohorts support the existence of “delayed mobility” among baby boomers.

The Demographic Cycle and Optimal Schooling Choices

A model is developed that enables the authors to estimate the effects of demographic cycles on both earnings and schooling. The model is tested using data from the 1991 Korean Occupational Wage Survey. The results indicate that cohorts following large birth cohorts in the cycle choose relatively less formal schooling compared to pre-peak cohorts, and that post-peak cohorts also have lower incomes. This result concerning South Korea is consistent with findings from previous studies concerning the United States.

Social Change and Land Use in Prehistoric Dalmatia

The Neothermal Dalmatia Project is an Anglo-Yugoslav collaborative project whose aims are to define and explain changes in physical environment, settlement pattern and social structure in north Dalmatia over the last 12 millennia. The Project's fieldwork included archaeological field survey, analytical survey, trial excavation of Neolithic, Copper Age, Bronze Age, Iron Age and Roman sites, soil and land use mapping, ethnographic survey of modern villages and hamlets and palaeoenvironmental reconstructions (pollen, sediments, sea-level change, etc.). Within the long-term constraints of a limestone-dominated study region, the short-term events and medium-term agrarian and demographic cycles of the Dalmatian social groups have been studied in an inter-disciplinary manner. In this article, an attempt is made to examine the environmental and archaeological data within the frameworks of four explanatory models: the Land Use Capability (LUC) Model, the Cyclic Intensification–Deintensification (CID) Model, the Communal Ownership of Property (COP) Model and the Arenas of Social Power (ASP) Model. In the LUC model, reconstructions of past land use capabilities are used to derive postdictions of the most likely settlement patterns for successive periods (Neolithic–Roman); a high degree of postdictive success is met. In the CID model, Bintliff's model of cyclic variations in agricultural intensification and private land-holding is refined and tested against survey and excavation data. In the COP model, Fleming's model of communal land ownership is tested against similar data, with contrasting results. Finally, the ASP model is used to explain the expanded range of arenas of social power which develops from a place-based worldview in the early farming period. The conjoint use of these four explanatory models, which operate at different scales of duration, provides a broader basis for understanding changes in the prehistory of north Dalmatia in the Neothermal period than had previously been constructed.

Schooling Choices and Demographic Cycles

This paper examines the effect of demographic cycles on schooling choices and the timing of school completion. Utilizing data from the [U.S.] National Longitudinal Surveys of Labor Market Experience and from the Panel Study of Income Dynamics we find that men and women born during the upswing of a demographic cycle obtain more schooling and take longer to finish a year of schooling than comparable individuals born during the downswing of a demographic cycle. The patterns that we document are more complex than would be predicted by any of the theoretical models of educational responses to demographic cycles that have been presented in the literature. (EXCERPT)

Demographic Seasonality and Development: The Effects of Agricultural Colonialism in Taiwan, 1906–1942

Nearly all developed countries have experienced dramatic declines in the seasonality of demographic behavior over the last century. This article examines seasonal behavior in the population of Taiwan between 1906 and 1942, during Japanese colonial rule. First, we analyze seasonal demographic cycles and their ties to the cultural calendar and agriculture. Second, we compare seasonality in two regions (Xinzhu and Tainan) that experienced different agricultural development under the colonial regime. Findings demonstrate that demographic seasonality was less pronounced when urban development and colonial agricultural intensification produced more heterogeneous seasonal patterns of labor. We find that changes in agricultural organization, rather than purely a shift to nonagricultural production, may significantly reduce established seasonal timing of demographic behavior.

Urban Systems by the Third Millennium: A Second Look

Abstract A second look is taken at “The Geography of the U.S. in the Year 2,000.” A new interplay is seen of the countervailing pressures to disperse and to agglomerate. Polynucleated urban regions are seen, organized within and around a global poly center. There are certain imperatives: those of demographic cycles and of the economic long wave. These will interact with information-age technologies to change family structures, life styles, and locational preferences. The unexpected also should be expected: “catastrophes” in which existing arrangements are transformed and new structures put into place to replace them. A key to understanding is to continually probe the second derivatives: change in the nature of change.

Demographic Cycles, Cohort Size, and Earnings

This article examines whether position in the demographic cycle is an important factor in determining earnings and earnings growth. Earnings equations for white males are estimated by using March Current Population Survey data. Position in the demographic cycle is captured by including both measures of own cohort size and the size of surrounding cohorts in the estimated earnings equations. Position in the demographic cycle matters. Increases in own cohort size lead to flatter earnings profiles, whereas increases in the size of surrounding cohorts are associated with steeper earnings profiles. The net effect is that those who enter the labor market before or after the peak of the demographic cycle start out with lower earnings but experience faster earnings growth. This pattern is uniform across all schooling groups: high school dropouts, high school graduates, those with some college, and college graduates.

Stable Demographic Limit Cycles in Laboratory Populations of Tribolium castaneum

Stable Demographic Limit Cycles in Laboratory Populations of Tribolium castaneum

Leveling the Peaks and Troughs in the Demographic Cycle: An Application to School Enrollment Rates

The relationship between demographic cycles and school enrollment rates in the United States is explored. The authors show how individuals act so as to fill in the peaks and troughs of the demographic cycle by timing their entry into the labor market through education. It is suggested that those born at the beginning of the baby boom are likely to have the highest school enrollment rates while those born at the end are likely to have the lowest rates. This asymmetric demographic effect is tested in a time series equation. [The] model helps to explain the surprisingly steep decline in school enrollment rates during the 1970s. (EXCERPT)

The Stimulating Effect of a Phytohormone, Gibberellic Acid, on Reproduction of Mus musculus

The plant hormone gibberellic acid (GA3), given in the drinking water to field-caught Mus musculus in the laboratory, almost doubled the proportion of females producing litters. No increase was detected in litter size or number of litters produced by breeding females. In a further experiment, the proportion of females coming into oestrus was more than doubled by treatment with GA3. Present in many plants, especially during germination, growth and seed maturation, gibberellins may be proximate chemical cues to reproduction in some herbivores, and may act as a feedback mechanism between plant and herbivore in some models of demographic cycles.