Effects Of Age Structure Research Articles

Are Older Workers Harmful for Firm Productivity?

This paper investigates the effects of the workforce age structure on the productivity of large Belgian firms. More precisely, it examines different scenarios of changes in the proportion of young (16–29 years), middle-aged (30–49 years) and older (more than 49 years) workers and their expected effects on firm productivity. Using detailed matched employer–employee data, we find that young workers are significantly more productive than older workers. Yet, results also show that age structure effects on productivity: (i) have substantially decreased over time and (ii) are much stronger in ICT than in non-ICT firms.

Are Young and Old Workers Harmful for Firm Productivity?

This paper investigates the effects of the workforce age structure on the productivity of large Belgian firms. More precisely, it examines different scenarios of changes in the proportion of young (16-29 years), middle-aged (30-49 years) and old (more than 49 years) workers and their expected effects on firm productivity. Using detailed matched employer-employee data, we find that a higher share of young (old) workers within firms is favourable (harmful) for firm value added per capita. Results also show that age structure effects on productivity are stronger in ICT than in non-ICT firms.

Macroeconomic Implications of Demography for the Environment: A Life-Cycle Perspective

This article studies how demography affects the outcome of the environmental policy in a macro-economic perspective, incorporating age-earning profiles in an OLG model a la Blanchard (1985) to capture the age structure effect of the demographic shocks. It first demonstrates, conversely to previous works of the related literature that a decrease in the birth rate may lower the steady-state per capita stock of physical capital even if the aggregate labor supply is exogenous. It also demonstrates that the ageing of population influences the macro-economic impact of the environmental policy according to the cause of the ageing and the life-cycle earnings assumption. Thus, with decreasing age-earning profiles, a lower birth rate reduces the detrimental impact of the environmental policy on the steady-state per capita stock of physical capital for low values of this birth rate, while a reduction of the mortality rate reinforces the negative outcome of the environmental policy. When earnings profiles are independent of age, ageing always strengthens the negative impact of the environmental policy.

Surplus production dynamics in declining and recovering fish populations

Surplus production rates predicted by simple biomass dynamics models are generally expected to follow a simple dome-shaped pattern as population size changes and to show similar trajectories during population decline and recovery. Age-structured models, however, predict substantially lower surplus production rates during population recovery than during decline because of reduced mean fecundity, unless recruitment compensation is very strong. Ecosystem models like Ecosim predict more complex patterns, with reduced production during recoveries due to both age-structure effects and cultivation–depensation effects related to changes in competitor and predator abundances. Production-driven recoveries, where surplus production per biomass is higher during recovery than decline, are predicted in cases where there has been substantial change in overall ecosystem productivity or community structure. 110 case examples illustrate that simple, repeatable relationships between stock size and production are uncommon, and the most common pattern is production-driven change in stock size, where changes in production rate apparently independent of stock size then drive stock increase or decrease. We conclude that nonstationarity in productivity needs to be considered as part of population rebuilding and that empirical estimates of surplus production may provide insight in this process.

Williams's Theory of the Evolution of Senescence: Still Useful at Fifty

George Williams indicated that he would not expect senescence to evolve in organisms that lack a distinction between germ line and soma. Escherichia coli--long assumed to lack even a hint of this distinction--is now known to senesce, posing what would seem to be a challenge to Williams's well-known theory of the evolution of senescence. However, in this review, I will show that cell division in E. coli produces a degree of germ-soma modularity sufficient to generate age structure and antagonistic pleiotropic effects, thereby satisfying the requirements of Williams's theory. From this perspective, senescence in E. coli is supportive and points the way to a better understanding of the pleiotropies that connect adaptive complexity and senescence. Sexual reproduction is but one of the complex adaptations illuminated by this approach.

The effects of age structure on economic growth: An application of probabilistic forecasting to India

During recent years there has been an increasing awareness of the explanatory power of population age structure variables in economic growth regressions. We estimate a new cross-country regression model of the effects of age structure change on economic growth. We use the new model and recent probabilistic demographic forecasts for India to derive the uncertainty of predicted economic growth rates caused by the uncertainty in demographic developments.

Structural Covariates of Homicide Rates

Most previous empirical comparative studies of homicide examine homicide rates across nations or subnational units within a single country. This study is the first in which a European cross-national city comparison is made. The article aims to provide insight into the extent that the homicide rates are related to the social and economic forces characterizing a sample of European cities. Derived from theories rooted in classic works, including social disorganization, strain, and urbanism, are six hypothesized effects of structural forces on homicide rates. Analyses show that cities' deprivation and population structure indexes are strong predictors of homicide rates. The predicted effects of unemployment rates, population heterogeneity, and age structure on homicide rates, however, were not consistently corroborated by these results. Comparing Eastern and Western European countries, the authors also find support for the influence of the country's level of development on city-level homicide rates.

Labor Market Rigidities and the Employment Behavior of Older Workers

The labor market is often asserted to be characterized by rigidities that make it difficult for older workers to carry out their desired trajectory from work to retirement. An important source of rigidity is restrictions on hours of work imposed by firms that use team production or face high fixed costs of employment. Such rigidities are difficult to measure directly. We develop a model of the labor market in which technological rigidity affects the age structure of a firm's work force in equilibrium. Firms using relatively flexible technology care only about total hours of labor input, but not hours of work per worker. Older workers with a desire for short or flexible hours of work are attracted to such firms. Firms using a more rigid technology involving team production impose a minimum hours constraint, and as a result tend to have a younger age structure. A testable hypothesis of the model is that the hazard of separation of older workers is lower in firms with an older age structure. We use matched worker-firm data to test this hypothesis, and find support for it. Specification tests and alternative proxies for labor market rigidity support our interpretation of the effect of firm age structure on the separation propensity. These results provide indirect but suggestive evidence of the importance of labor market rigidities.

Two‐species asymmetric competition: effects of age structure on intra‐ and interspecific interactions

1. The patterns of density-dependent resource competition and the mechanisms leading to competitive exclusion in an experimental two-species insect age-structured interaction were investigated. 2. The modes of competition (scramble or contest) and strength of competition (under- to overcompensatory) operating within and between the stages of the two species was found to be influenced by total competitor density, the age structure of the competitor community and whether competition is between stages of single or two species. 3. The effect of imposed resource limitation on survival was found to be asymmetric between stages and species. Environments supporting both dominant and subordinate competitors were found to increase survival of subordinate competitors at lower total competitor densities. Competitive environments during development within individual stage cohorts (i.e. small or large larvae), differed from the competitive environment in lumped age classes (i.e. development from egg-->pupae). 4. Competition within mixed-age, stage or species cohorts, when compared with uniform-aged or species cohorts, altered the position of a competitive environment on the scramble-contest spectrum. In some cases the competitive environment switched from undercompensatory contest to overcompensatory scramble competition. 5. Such switching modes of competition suggest that the relative importance of the mechanisms regulating single-species population dynamics (i.e. resource competition) may change when organisms are embedded within a wider community.

Consumption and population age structure

In this paper, the effects on aggregate consumption of changes in the age distribution of the population are analysed empirically. Economic theories predict that age influences individuals’ saving and consumption behaviour. Despite this, age structure effects are rarely controlled for in empirical consumption functions. Our findings suggest that they should. By analysing Norwegian quarterly time series data, we find that changes in the age distribution of the population have significant and life-cycle-consistent effects on aggregate consumption. Furthermore, controlling for age structure effects stabilises the other parameters of the consumption function and reveals significant real interest rate effects.

Globally attracting attenuant versus resonant cycles in periodic compensatory Leslie models

We use a periodically forced density-dependent compensatory Leslie model to study the combined effects of environmental fluctuations and age-structure on pioneer populations. In constant environments, the models have globally attracting positive fixed points. However, with the advent of periodic forcing, the models have globally attracting cycles. We derive conditions under which the cycle is attenuant, resonant, and neither attenuant nor resonant. These results show that the response of age-structured populations to environmental fluctuations is a complex function of the compensatory mechanisms at different life-history stages, the fertile age classes and the period of the environment.

Population age structure and real exchange rates in the OECD

Macroeconomic theory predicts that variations in population cohort sizes will lead to demographically induced real exchange rate movements. While such effects have previously been established for individual countries, this paper exploits cross-sectional time series data to test the prediction for a larger number of economies. A reduced form model with population age shares as regressors is estimated using a panel of 25 OECD countries between 1971 and 2002. The results confirm that demographic structure has significant explanatory power for the real exchange rate and the estimated relationship supports age structure effects in accordance with the life cycle hypothesis.

Plastic changes in seed dispersal along ecological succession: theoretical predictions from an evolutionary model

SummaryWe use a deterministic model to explore theoretically the ecological and evolutionary relevance of plastic changes in seed dispersal along ecological succession. Our model describes the effect of changing disturbance regime, age structure, density and interspecific competition as the habitat matures, enabling us to seek the evolutionarily stable reaction norm for seed dispersal rate as a function of time elapsed since population foundation.Our model predicts that, in the context of ecological succession, selection should generally favour plastic strategies allowing plants to increase their dispersal rate with population age, contrary to previous predictions of models that have assumed genetically fixed dispersal strategies.More complex patterns can evolve showing periods with high production of dispersing seeds separated by periods of intense local recruitment. These patterns are due to the interaction of individual senescence with change in ecological conditions within sites.Evolution of plastic dispersal strategies affects the patterns of density variation with time since foundation and accelerates successional replacement. An interesting parallel can be drawn between the evolution of age‐specific dispersal rates in successional systems and the evolution of senescence in age‐structured populations.Seed dispersal plasticity could be a potential mechanism for habitat selection in plants and have implications for range expansion in invasive species because recently founded populations at the advancing front may show different patterns to those in the established range.

Giving Credit where Credit is Due. A Practical Method to Distinguish between Human and Natural Factors in Carbon Accounting

Net carbon emissions from the biosphere differ from fossil-fuel based emissions in that: (i) a large proportion of biospheric carbon exchange is not under direct human control; (ii) land-use decisions often have only a small short-term effect on net emissions, but a large long-term effect; and (iii) biospheric carbon exchange is potentially reversible. Because of these differences, carbon accounting approaches also need to be different for fossil-fuel and biosphere-based emissions. Recognising that, the international negotiators at COP 7 adopted a range of guiding principles for accounting for biospheric carbon exchange, including: “that accounting excludes removals resulting from (a) elevated carbon dioxide concentrations above pre-industrial level; (b) indirect nitrogen deposition; and (c) the dynamic effects of age structure resulting from activities and practices before the reference year.” In this paper, we highlight some of the challenges in biospheric carbon accounting for Canada, the U.S.A, New Zealand and Australia, four nations for which biospheric net carbon exchange is large relative to fossil-fuel based emissions. We discuss an accounting scheme that is based on assessing changes in average carbon stocks due to changes in land use. That scheme is tailored to the special needs of biospheric carbon management and is consistent with the accounting principles adopted at COP 7. The paper shows how the accounting scheme would resolve many of the biospheric carbon accounting anomalies identified for the four nations we studied.

Age effects in Swedish local labor markets

The paper studies age structure effects on local labor market performance. Results show that young workers benefit from large youth cohorts and that a one standard deviation increase in the share of workers aged 50–60 years raises overall unemployment by 1.1 percentage points.

Youth dependency and total factor productivity

Recent literature shows empirical support for an effect of demographic age structure on economic growth. This literature does not give attention to the possibility that age structure might also have an effect on total factor productivity. Much of the recent literature on economic growth has stressed that an understanding of cross-country differences in output per worker is needed. That literature argues that the most important determinant of international differences in output per worker is differences in total factor productivity. This paper finds empirical evidence in cross-country data for the thesis that the youth dependency ratio (the population below working age divided by the population of working age) reduces ‘residual’ growth, which measures total factor productivity growth. For this reason, the paper demonstrates that age structure has an effect on the most important determinant of international differences in output per worker.

Simulating the Effect of Landscape Size and Age Structure on Cavity Tree Density Using a Resampling Technique

Abstract Cavity-tree density (CTD) is an important indicator of habitat quality for cavity-dependent wildlife. However, the abundance of cavities and cavity trees can vary dramatically, even among trees or stands with similar attributes. This uncertainty can make it difficult to expand stand-levelestimates of cavity abundance to large landscapes, although it is often desirable to do so. This limits the utility of CTD as a measure of habitat quality. We use a resampling method (statistical bootstrap) to construct a set of regression models to predict CTD based on landscape age structureand landscape size. The estimated regression coefficients are highly variable (in terms of the adjusted R2 and root mean square error) for landscapes <100 ha, but the models perform well for larger landscapes. We test the regression models using an independent data set from theMissouri Ozark Forest Ecosystem Project (MOFEP) and find that the mean relative error (RE) when predicting CTD for landscapes between 300 and 4,000 ha is less than 10%. Both the size (in hectares) of the landscape and the stand age-class components affect RE; but RE decreases with increasinglandscape size in a consistent and quantifiable manner. For Ozark landscapes ≥100 ha, knowledge of the proportion of the area in the seedling/sapling, pole, sawtimber, and old-growth age classes can be used to readily estimate the number of cavity trees and how that number will change ifthe landscape age structure is altered. FOR. SCI. 50(5):603–609.

Are Predators Good for Your Health? Evaluating Evidence for Top-down Regulation of Zoonotic Disease Reservoirs

Zoonotic diseases, caused by pathogens transmitted to people from vertebrate reservoirs, take an enormous toll on human health worldwide. Many of these disease agents are harbored in rodent populations, and humans are victims of “accidental” transmission. Here we explore the idea that predatory vertebrates indirectly protect human health by reducing population size of rodent reservoirs of human disease. Research frontiers include the importance of rodent population density to the incidence of human disease, as opposed to behavior or age structure effects; the roles of different types of predators in determining both population dynamics and rodent density per se; and the effects of human-caused environmental change on predators and their rodent prey. A better understanding of these basic ecological issues will inform both environmental and health policy.

Are predators good for your health? Evaluating evidence for top-down regulation of zoonotic disease reservoirs

Zoonotic diseases, caused by pathogens transmitted to people from vertebrate reservoirs, take an enormous toll on human health worldwide. Many of these disease agents are harbored in rodent populations, and humans are victims of “accidental” transmission. Here we explore the idea that predatory vertebrates indirectly protect human health by reducing population size of rodent reservoirs of human disease. Research frontiers include the importance of rodent population density to the incidence of human disease, as opposed to behavior or age structure effects; the roles of different types of predators in determining both population dynamics and rodent density per se; and the effects of human-caused environmental change on predators and their rodent prey. A better understanding of these basic ecological issues will inform both environmental and health policy.

The Effects of Genetic and Geographic Structure on Neutral Variation

▪ Abstract Variation within a species may be structured both geographically and by genetic background. We review the effects of such structuring on neutral variants, using a framework based on the coalescent process. Short-term effects of sex differences and age structure can be averaged out using fast timescale approximations, allowing a simple general treatment of effective population size and migration. We consider the effects of geographic structure on variation within and between local populations, first in general terms, and then for specific migration models. We discuss the close parallels between geographic structure and stable types of genetic structure caused by selection, including balancing selection and background selection. The effects of departures from stability, such as selective sweeps and population bottlenecks, are also described. Methods for distinguishing population history from the effects of ongoing gene flow are discussed. We relate the theoretical results to observed patterns of variation in natural populations.