Estimating growth and mortality in stage-structured populations

This paper presents a practical numerical method for separatingand estimating growth and mortality coefficients in stage- orsize-structured populations using only observations of the relativeor absolute abundance of each stage. The method involves writinga system of linear ordinary differential equations (ODEs) modellingthe rate of change of abundance. The solution of the differentialsystem can be numerically approximated using standard (e.g.sixth-order Runge-Kutta-Felhberg) methods. An optimization problemwhose solutions yield ‘optimal’ coefficients fora given model is formulated. The ODE numerical integration techniquecan then be employed to furnish required function and gradientinformation to the optimization algorithm. The data-fittingsoftware package ODRPACK is then successfully employed to estimateoptimal coefficients for the ODE population model. Simulationexperiments with four- and eight-stage model populations illustratethat the method results in the successful estimation of coefficientsof mortality and growth from abundance data.     

Palaenutritional studies on skeletal remains of ancient populations from the Mediterranean area: an attempt to interpretation

As indicators of dietary status, standardised levels of strontium and zinc in specimens of bones from several prehistoric and historic sites in Europe are compared. The bone level of strontium reflects the vegetable intake in the diet, the level of zinc that of foods of animal origin. The large quantities of plants in the diet of palaeolitic hunters gave way in the mesolithic to an almost exclusively vegetarian diet, but then an increase in meat consumption in the neolithic. Agricultural economies characterised classical Greece and Rome, but the big towns were able to maintain a mixed diet. In the early centuries AD there was a decline in agricultural consumption.     

Fractionation of Escherichia coli cell populations at different stages during growth transition to stationary phase

Cultures of Escherichia coli could be separated into more than 15 cell populations, each forming a discrete band after Percoll gradient centrifugation. The cell separation was found to result from the difference in buoyant density but not the size difference. The cell density increases upon transition from exponential growth to stationary phase. Exponential phase cultures formed at least five discrete bands with lower densities, whereas stationary phase cultures formed more than 10 bands with higher densities. Two molecular markers characterizing each cell population were identified: the functioning promoter species, as identified by measuring the expression of green fluorescent protein under the control of test promoters; and the expressed protein species, as monitored by quantitative immunoblotting. These findings together suggest that the growth phase-coupled transition of E. coli phenotype is discontinuous.     

Biological costs of economic transition: Stress levels during the transition from communism to capitalism in Poland

At the end of the 1980s, Poland began the transformation from an essentially one-party communist system to a politically pluralistic democratic system. These political and economic changes had major social consequences, among others unemployment and a sharp decrease in real personal income. The aim of the study was to investigate the possible relationship between stress in adult men, measured by the Allostatic Load, and the socio-economic deterioration during the first part of the economic transition. The Allostatic Load included eleven markers assessing adverse nutritional intake, cardiovascular activity, inflammatory processes, and lung, hepatic and renal functions. The results indicate a significantly higher risk of metabolic dysregulation in men examined after 1990, compared to men from previous years. After adjustment for socioeconomic variables and lifestyle variables, men examined in 1991 had a 31% greater risk of higher Allostatic Load compared with men examined in 1985 (OR = 1.31; p = 0.0541), in 1992, this risk was 50% greater (OR = 1.50; p < 0.01), and in 1993, the risk was 66% greater (OR = 1.66; p < 0.05). The conclusion is drawn that significantly more stressogenic factors for men were those directly connected with the financial situation of their families, than a sudden but short increase of prices for goods and services.     

A craniometric perspective on the transition to agriculture in Europe

Debates surrounding the nature of the Neolithic demographic transition in Europe have historically centered on two opposing models: a "demic" diffusion model whereby incoming farmers from the Near East and Anatolia effectively replaced or completely assimilated indigenous Mesolithic foraging communities, and an "indigenist" model resting on the assumption that ideas relating to agriculture and animal domestication diffused from the Near East but with little or no gene flow. The extreme versions of these dichotomous models were heavily contested primarily on the basis of archeological and modern genetic data. However, in recent years a growing acceptance has arisen of the likelihood that both processes were ongoing throughout the Neolithic transition and that a more complex, regional approach is required to fully understand the change from a foraging to a primarily agricultural mode of subsistence in Europe. Craniometric data were particularly useful for testing these more complex scenarios, as they can reliably be employed as a proxy for the genetic relationships among Mesolithic and Neolithic populations. In contrast, modern genetic data assume that modern European populations accurately reflect the genetic structure of Europe at the time of the Neolithic transition, while ancient DNA data are still not geographically or temporally detailed enough to test continent-wide processes. Here, with particular emphasis on the role of craniometric analyses, we review the current state of knowledge regarding the cultural and biological nature of the Neolithic transition in Europe.     

Estimating cladoceran birth rate: use of the egg age distribution to estimate mortality of ovigerous females and eggs

The birth rate of natural cladoceran populations can change rapidly (during 2–3 days), reflecting rapid changes in their environment. If the egg ratio is calculated on the basis of egg age distribution, the birth rate can be estimated at short sampling intervals (shorter than egg stage duration) by modified Paloheimo's (1974) formula. When female size structure and age of eggs in clutches at the beginning and the end of a sampling interval are known, death rates of ovigerous females and eggs in separate size classes can be determined and incorporated in birth rate estimates. All these methods have been employed using the data on the population of Diaphanosoma brahyurum from the lake Obsterno (North-Western Belarus) in July–August, 1992. The birth rate values computed by the proposed methods and Poloheimo's formula differed significantly in many cases. The accuracy of birth rate estimations from various calculation methods was tested using a computer simulation. The model contains the essential features of cladoceran life history: distinct egg, juvenile and adult stages, development of eggs and reproduction. The population was divided into 25 age classes, each of 1 day duration. Durations of the egg, juvenile and adult stages were set at 3, 6 and 20 days, respectively. The embryogenesis was divided into three egg stages, each of 1 day duration. Survivorship was set from 0.2 up to 1.0 for each age class. The survivorship and brood size were changed through each of five time intervals (days) that allowed to simulate an increase or reduction of population density. Fecundity, survivorship and egg stage duration remained constant during each of 5 days that assumed stability of an environment (this does not occur in nature). Nevertheless, the egg ratio, proportion of juveniles and birth rates were variable even under these circumstances. Computer simulations showed that Poloheimo's formula evaluates birth rate with the relative error of 62% and usually overestimates its values. We propose methods to decrease errors of birth rate estimations by 3.5–5.5 times.     

Neighbour-regulated mortality: the influence of positive and negative density dependence on tree populations in species-rich tropical forests

Density‐dependent mortality has long been posited as a possible mechanism for the regulation of tropical forest tree density. Despite numerous experimental and phenomenological investigations, the extent to which such mechanisms operate in tropical forests remains unresolved because the demographical signature of density dependence has rarely been found in extensive investigations of established trees. This study used an individual‐based demographical approach to investigate the role of conspecific and heterospecific neighbourhood crowding on tree mortality in a Panamanian and a Malayan tropical forest. More than 80% of the species investigated at each site were found to exhibit density‐dependent mortality. Furthermore, most of these species showed patterns of mortality consistent with the Janzen–Connell hypothesis and the rarely explored hypothesis of species herd protection. This study presents some of the first evidence of species herd protection operating in tree communities.     

The influence of calcium on aluminium-induced changes in the growth rate and mortality of brown trout, Salmo trutta L.

Yearling brown trout, Salmo trutta L., were maintained in a synthetic medium at pH 5.2 with various concentrations of calcium (4–400 μumol l⁻¹) and aluminium (0–3 μumol l⁻¹). In general, higher mortality and lower growth rates were found at higher aluminium concentrations, with these effects being reduced at high ambient calcium. Aluminium toxicity was greater in an experiment conducted in February–March than in an experiment conducted in October–December; this could be due to a seasonal variation in tolerance of the fish. Aluminium exposure resulted in an initial period of weight loss and high mortality followed by some recovery over the 6-week period of the experiments. In the first experiment, as in previously reported work, adaptation was incomplete in that aluminium-induced growth rate reduction was still evident to the end of the test. In the second experiment, however, no significant effect of aluminium treatment on growth was found during weeks 4 to 6 of the exposure period.     

Soil management effects on entomopathogenic fungi during the transition to organic agriculture in a feed grain rotation

The growing demand for organic products creates opportunities for farmers. Information on the consequences of management practices can help farmers transition to organic and take advantage of these prospects. We examined the interaction between soil disturbance and initial cover crop on naturally occurring entomopathogenic fungi (EPF) during the 3-year transition to organic production in a feed grain rotation in central Pennsylvania. Our experiment included four systems comprised of a factorial combination of two levels of primary tillage (full vs. reduced) and two types of initial cover crop (timothy/clover vs. rye/vetch). The cropping sequence consisted of an initial cover crop, followed by soybean, and finally, maize. The entire experiment was replicated in time, with the initiation lagged by 1 year. We detected four species of EPF (Metarhizium anisopliae, Beauveria bassiana, Isaria fumosorosea, and Isaria farinosa) by bioassay of soil samples collected four times during each field season. The latter three species were detected infrequently; therefore, we focused statistical analysis on M. anisopliae. Detection of M. anisopliae varied across sampling date, year in crop sequence, and experimental start, with no consistent trend across the 3-year transition period. M. anisopliae was isolated more frequently in the systems initiated with timothy/clover cover crops and utilizing full tillage; however, we only observed a tillage effect in one temporal replicate. M. anisopliae detection was negatively associated with soil moisture, organic matter, and zinc, sulfur, and copper concentrations in the soil. This study helps to inform farmers about management effects on soil function, specifically conservation biological control.     

Soil management effects on entomopathogenic fungi during the transition to organic agriculture in a feed grain rotation

The growing demand for organic products creates opportunities for farmers. Information on the consequences of management practices can help farmers transition to organic and take advantage of these prospects. We examined the interaction between soil disturbance and initial cover crop on naturally occurring entomopathogenic fungi (EPF) during the 3-year transition to organic production in a feed grain rotation in central Pennsylvania. Our experiment included four systems comprised of a factorial combination of two levels of primary tillage (full vs. reduced) and two types of initial cover crop (timothy/clover vs. rye/vetch). The cropping sequence consisted of an initial cover crop, followed by soybean, and finally, maize. The entire experiment was replicated in time, with the initiation lagged by 1 year. We detected four species of EPF (Metarhizium anisopliae, Beauveria bassiana, Isaria fumosorosea, and Isaria farinosa) by bioassay of soil samples collected four times during each field season. The latter three species were detected infrequently; therefore, we focused statistical analysis on M. anisopliae. Detection of M. anisopliae varied across sampling date, year in crop sequence, and experimental start, with no consistent trend across the 3-year transition period. M. anisopliae was isolated more frequently in the systems initiated with timothy/clover cover crops and utilizing full tillage; however, we only observed a tillage effect in one temporal replicate. M. anisopliae detection was negatively associated with soil moisture, organic matter, and zinc, sulfur, and copper concentrations in the soil. This study helps to inform farmers about management effects on soil function, specifically conservation biological control.     

The natural regulation of buffalo populations in East Africa: III. Population trends and mortality*

Analysis is carried out on the population data obtained from censuses and estimates of fertility and recruitment for the years 1965–1972, From the analysis, adult mortality is the only detectable reduction which acts as a negative feedback on the population, and is the only one needed to regulate the population in a way similar to the observed population trends. From a frequency distribution of ages at death, an approximate composite life table is constructed. This shows that males and females have similar age-specific mortalities until old age, but then males survive relatively better. Information on the causes of mortality indicate that the regulating adult mortality is caused in part by undernutrition, which in turn is due to food limitation rather than to social and physiological factors. Predation causes only a small part of the annual adult mortality, and its effect is swamped by other factors. Diseases play an important part as a primary factor in juvenile mortality but not in adult mortality because of the development of immunity. However, both disease and predation are important as secondary agents killing adults already weakened by moderate undernutrition. It is suggested that they play an essential role by hastening the population's response to changes in the food supply, and hence dampening oscillations that might develop in population and resource.     

Estimating the influence of population density and dispersal behavior on the ability to detect and monitor Agrilus planipennis (Coleoptera: Buprestidae) populations

Emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), a phloem-feeding pest of ash (Fraxinus spp.) trees native to Asia, was first discovered in North America in 2002. Since then, A. planipennis has been found in 15 states and two Canadian provinces and has killed tens of millions of ash trees. Understanding the probability of detecting and accurately delineating low density populations of A. planipennis is a key component of effective management strategies. Here we approach this issue by 1) quantifying the efficiency of sampling nongirdled ash trees to detect new infestations of A. planipennis under varying population densities and 2) evaluating the likelihood of accurately determining the localized spread of discrete A. planipennis infestations. To estimate the probability a sampled tree would be detected as infested across a gradient of A. planipennis densities, we used A. planipennis larval density estimates collected during intensive surveys conducted in three recently infested sites with known origins. Results indicated the probability of detecting low density populations by sampling nongirdled trees was very low, even when detection tools were assumed to have three-fold higher detection probabilities than nongirdled trees. Using these results and an A. planipennis spread model, we explored the expected accuracy with which the spatial extent of an A. planipennis population could be determined. Model simulations indicated a poor ability to delineate the extent of the distribution of localized A. planipennis populations, particularly when a small proportion of the population was assumed to have a higher propensity for dispersal.     

The correlation of the indices of animal longevity and mortality in stationary populations with a constant rate of mortality

Equations have been derived on the basis of general ratios of the numbers of different age groups of animals that allow to estimate the mortality coefficient in populations with stationary age structure and intensity of mortality that does not depend on age at their continuous and discontinuous replenishing by frequency of occurrence of individuals of the maximal age. The proposed method of estimation of mortality has been tested on models with different numbers of animals and age classes. The equation gives a non-biased estimate of mortality coefficient for populations with discontinuous replenishing with young individuals at very small sample sizes (less than 10 individuals).     

Submandibular salivary glands: influence on growth rate and life span in mice

Submandibular glands accumulate a variety of growth factors, especially in male mice. Surgical excision of these glands (sialoadenectomy) results in alterations in several organs and systems including the liver, skin and reproductive system. We studied the life-long consequences of sialoadenectomy in male mice. Animals were operated at the age of 10 weeks. Thereafter, body weight and food and water intake were controlled until death. Few weeks after surgery, body weight was lower in sialoadenectomized than in control mice. The difference remained stable until the age of 80 weeks. In spite of the lower body weight, food intake was higher in sialoadenectomized mice than in controls. The first death of sialoadenectomized mice occurred 10 weeks earlier than that of the first control, and the initial death rate in sialoadenectomized mice was almost twice the rate in controls. After 100 weeks of life, the death rate increased in control mice, but suddenly decreased in sialoadenectomized mice. The consequence was that the mean life span of the last 25% surviving animals was 10 weeks longer in sialoadenectomized than in control mice. Autopsy examination suggests that the effect of sialoadenectomy on death rate may be the consequence of a contrasting effect on tumour growth. Our results indicate that submandibular glands, or rather the factors derived from these glands, have contrasting roles in tumour growth. At early ages they may be survival factors and protect tissues, whereas at later ages they may stimulate the growth of transformed cells.     

Diurnal trends in net photosynthetic rate and carbohydrate levels of soybean leaves

A study was made of diurnal trends in net photosynthetic rate and carbohydrate levels of unifoliolate leaves of soybean (Glycine max L. Merrill) under constant environmental conditions (50,000-lux light intensity, 24.5 C air temperature, 60% relative humidity, and 300 microliters of CO₂ per liter of air).     

Some recent trends in infant mortality in the province of Marrakech, Morocco: a demographic transition in process

2 studies designed to appraise fecundity and mortality were carried out in Morocco in 1983 and 1984, on samples of 3,000 and 5,000 women respectively, in the city and in the province of Marrakech. Infant mortality was studied using the biometric method of J. Bourgeois-Pichat. The 1st results presented in this article highlight the absence of excess exogenous mortality among women under 30 years of age living in a provincial urban environment and among women from the city of Marrakech whose husbands were employed in service activities. 1st, this points to a link between the level of exogenous mortality and the standard of living of the population. In the city, exogenous mortality varies according to the occupation of the head of the family, an important factor in estimating its economic level. In the province one can assume that the standard of living of women from urban areas is higher than in the country. Moreover, small urban centers benefit from a larger infrastructure with easier access to medical care. 2nd, mortality has declined among young women. This result is certainly closely linked to the improvement of living conditions in Morocco over the last 2 decades. It is therefore reasonable to consider that a demographic transition is taking place, one which impacts on the level and structure of infant mortality.