Persistence of abnormal females that produce only female progeny with occasional recovery to normal females in Lepidoptera

In Lepidoptera, females that produce only female progeny have been found in wild populations of at least 12 species. In some species, recoveries, where abnormal females return to normal females, have been observed. A mathematical model of the population dynamics with recovery was developed to identify the conditions for realizing the persistence of abnormal females. Analysis indicated normal and abnormal females coexist and reach an equilibrium state at certain recovery rate values. The equilibrium values of normal and abnormal females were determined. When a population was in equilibrium it was shown that the ratio of normal to abnormal females and the sex ratio after reproduction are always functions of the recovery rate and the proportion of female offspring from an abnormal female to that from a normal female. Using the simulation it was found that, even when a population fluctuates under variable environmental conditions, the two ratios mentioned above reach equilibrium. Equilibrium relationships were applied to published data, and it was concluded that recovery from abnormal to normal females explains the persistence of abnormal females in some species of Lepidoptera. The model developed in this paper can also be used for analysing the persistence of abnormal females of other insect species.     

Variation in offspring size within a population of the web-building spiderAgelena limbata

Within a population of the web-building spiderAgelena limbata, the weight of the first instar nymphs ranged from 1.187 to 6.559 mg. Both intraclutch and interclutch variation were recorded. The mean weights were different among clutches and the coefficients of variation within a clutch ranged from 3.3 to 29.2%. Variation in the nymphal weight was certainly derived from variation in the egg weight because there was a high correlation between the two weights. Factors affecting interclutch variation in nymphal weight were examined by multiple regression analysis. Nymphal weight was positively correlated with the body size and food conditions of female parents, and negatively correlated with the clutch size. Among these three factors, the food conditions of female parents had the largest apparent effect on the interclutch variation. The results suggest that females with larger body size and more food produce larger offspring, and that there is a trade-off between offspring size and clutch size. Heavier nymphs had larger body size (carapace width) and may have larger energy reserves. Heavier nymphs survived experimental starvation for a significantly longer period.     

Why Is Fertility Lower in Wealthier Countries? The Role of Relaxed Fertility‐Selection

Lower fertility in wealthier countries can be explained in evolutionary terms by three key factors: (i) higher fertility in poorer countries—an evolutionary consequence of many generations of intense “fertility‐selection” favoring innate behaviors promoting high fertility, especially in males; (ii) the empowerment of women in wealthier countries that serves to reduce fertility directly—an evolutionary consequence of selection favoring an inherent preference for lower fertility in females, combined with release from the evolutionary effects of a long history of male control over female fertility; and (iii) offspring access in wealthy countries to public health care, welfare, and other social services, which combined with inherited wealth for offspring, virtually eliminates competition between families for the resource needs of offspring. The combined consequences of (ii) and (iii) mean that the fertility‐selection so prevalent in poor countries is relaxed in wealthy countries, thus allowing random genetic drift to produce an increased relative frequency of innate behaviors promoting low fertility and discontentment with high fertility.     

Population dynamics of a phytophagous lady-beetle,Epilachna vigintioctopunctata (Fabricius), living in spatio-temporally heterogeneous habitats. III. Effects of habitat structure on population dynamics

Temporal changes in the population size of a phytophagous lady-beetle were analyzed to identify mechanisms affecting lady-beetle population dynamics at different spatial scales. The study area (15 ha) included 18 habitat patches. The major host plants were potato for first generation larvae and eggplant for second generation larvae. The habitat patches were classified into three groups according to the major host plants in each patch: P-E patches (both host plants available), P patches (potato only), and E patches (eggplant only). The winter disappearance of adults in the whole study area, and larval mortality in E patches were apparently the most important factors disturbing the overall population density. Density-dependent movement of females appeared to have the greatest stabilizing effect on the yearly fluctuation of population density. Rate of increase of female adults from the first to the second generation,R, was generally higher on eggplants in E patches than in P-E patches because the adult density of the first generation was much higher in P-E patches. The yearly fluctuation of adult density in each generation tended to be less in patches with all habitat components necessary for the full life cycle (P-E patches). However, such patches were not favorable for first generation females, as indicated by the lower rate of increase from the first to the second generation. The density and stability of lady-beetle populations is discussed in relation to habitat structure.     

Fertility decline and female chances of marriage in Malaya

A feature of the demographic pattern of post-World War II Malaya has been its high rate of natural growth, which reached 31/2 per cent per annum in the mid-1950s. However, the average age at marriage of the female population has been rising for most of this period, and since 1956 there has been a considerable and sustained fall in the birth rate.

In this paper simple models are developed to show that in a closed population a continuing high rate of population growth is incompatible with a pattern of universal female marriage, monogamy and a culturally imposed age difference of considerable size between spouses. The demonstration provided by the models is then offered as at least a partial explanation of the fertility and female marriage trends in contemporary Malaya. Discrepancies between the population of Malaya and the models have to be taken into account. A pattern of polygamous and unstable marriage does exist amongst the Malaysians and, to a much lesser extent, in the Chinese community. Furthermore, recent years have witnessed the passing of the large surplus of single males built up in the Chinese sector of the population during the years oflarge scale immigration. Such a transition is well under way in the Indian community too.

It is suggested that a substantial average age gap between spouses may be an aspect of many contemporary societies which reacts against the persistence of extremely high rates of natural increase. Even where demographic pressures in the ‘marriage market’ act towards a lessening of this gap, there is a cultural lag, during which period many females are forced to marry late or not at all.

Most of the study was made on a pan-Malayan basis (i.e. combining the Federation of Malaya and the State of Singapore) to achieve comparability with earlier censuses and as a recognition that with unrestricted migration between these areas they still form a single demographic unit. The terms Malaya and Malayans will be used when referring to this area or its inhabitants. The so-called major races of the country are Malaysians, Chinese and Indians. The first will be used in accordance with the census definition to cover the indigenous inhabitants of Malaya or the Malay Archipelago (Indonesia, British Borneo and the Philippines). As most of these people are either indigenous or have been in Malays for some generations they are usually called Malays (except for the aborigines). However, the all-embracing census term will be used here. Indians, in conformity with most local usage, will be used for the groups classified as Indians and Pakistanis at the 1957 censuses of the Federation of Malaya and Singapore. The group was very small.     

性别差异视角下的流动人口迁移距离及其影响因素 ——基于对上海流动人口的分析

通过对流动人口迁移距离性别差异的考察发现:(1)女性流动人口的平均迁移距离长于男性23.1千米,个体因素、迁移特征、经济社会因素对男性、女性流动人口的迁移距离存在着不同方向和不同程度的影响。少数民族和农村户籍的女性流动人口的迁移距离明显长于男性。(2)随受教育程度的提高,女性迁移距离不断增加,初中、高中、大学和研究生学历的女性流动人口的迁移距离分别增加0.062、0.058、0.098和0.170个单位。(3)女性流动人口的迁移受到距离的阻抗作用强度弱于男性,距离每增加1%,流入的女性流动人口规模降低1.090%,而男性为1.275%。(4)引入经济发展差距(GDP)和收入差距变量后,各变量的影响程度和方向发生变化,女性表现出学历、收入水平越高迁移得越远的特征。     

Insect migration: Variability and success in a capricious environment

Stochastic effects of climate and weather have a pervasive influence on the induction, performance and evolution of migration. In wing-dimorphic species, their influence on habitat quality, and on rates of development of the migrant itself, maintains variation in responses to environmental cues determining wing-form and migratory behaviour. Migrants flying above their flight boundary layer rely on winds to disperse them across landscapes in which their habitats are distributed. Patterns of distribution of habitat patches, and the influence of changing windspeeds and direction on the displacements of migrants, result in selection for variation in migratory potential at each migration. In subsequent migrations, this variation and stochastic effects of the winds on groundtracks of individual migrants ensure that their destinations ‘sample’ the landscapes they travel over. The extent and resolution of this sampling, by which migrants reach favourable habitats, depend on the components of migratory potential, their mode of inheritance, and genetic correlations between them, as well as on the characteristics of the winds on which they travel.     

A study of Irish county marriage rates, 1961-1966

Abstract This article considers a group of models of Irish county marriage rates. Some of these models account for the major part of the inter-county variation in male and female marriage rates in terms of the influence of a limited number of socio-economic variables. The sex ratio of the unmarried population in the counties plays a key role in all of the models: the female marriage rate tends to be raised, and the male rate lowered, by a high ratio of males to females in the unmarried population. Male rates appear to increase under more favourable economic conditions, as measured by county income per person, while female rates appear to be lowered by increased female participation in the labour force. In addition to these separate influences on male and female rates, a recursive model in which there is a one-way influence from male to female rates, and a simultaneous-equation model, in which male and female rates are fully interdependent, were tested. The performance of the tested recursive model was particularly satisfactory.     

Maternal age as a source of variation in the ability of an aphid to produce dispersing forms

Summary Apterous parthenogentic females of the pea aphid,Acyrthosiphon pisum (Harris), begin to produce alate offspring soon after they have been subjected to crowding. Females which were born early in their own parent's reproductive period respond most strongly to crowding, producing much larger numbers of alatae than their late-born sisters. In contrast, the early-born daughters of most alate females do not produce winged offspring after being crowded. Some of their later-born sisters may produce a few winged individuals, resembling in this respect the late-born daughters of the apterous females. Control of the production of alatae thus begins in the grandparental generation. Risk-spreading by means of differential dispersal becomes a less uncertain venture when local populations can modify their responses to environmental changes by utilizing past as well as present signals from their surroundings.     

Loss of genetic variability in a fragmented continuously distributed population

An individual-based simulation model was used to examine the effect of population subdivision, dispersal distance of offspring, and migration rates between subpopulations on genetic variability(H ₁ H _S andH _T ) in a continuously distributed population. Some difficulties with mathematical models of a continuously distributed population have been pointed out. The individual-based model can avoid these difficulties and can be used to examine genetic variability in a population within which individuals are distributed continuously and in which the dispersal of individuals is disturbed by geographical or artificial barriers. The present simulation showed that the pattern of decrease inH ₁ had three stages. During the first stage,H ₁ decreased at the rates predicted by Wright’s neighborhood size. During the second stage,H ₁ decreased more rapidly when the migration rate decreased, while during the third stage, it decreased less rapidly when the migration rate decreased. Increasing the number of subdivisions increased the rate of decrease after the 200th generation. The pattern of decrease inH _T was classified into 2 stages. During the first stage, the rates of decrease corresponded with those of a randomly mating population. During the second stage, a decrease in the migration rates of the subpopulations slowed the rate of decrease inH _T . A uniform spatial distribution and a reduced total dispersal distance of offspring causedH ₁ H _S , andH _T to decrease more rapidly. Habitat fragmentation in a continuously distributed population usually was detrimental to the genetic variability in the early generations. Other implications of the results for conservation are discussed.     

Kinship and Population Subdivision

The coefficient of kinship between two diploid organisms describes their overall genetic similarity to each other relative to some base population. For example, kinship between parent and offspring of 1/4 describes gene sharing in excess of random sharing in a random mating population. In a subdivided population the statistic F _st describes gene sharing within subdivisions in the same way. Since F _st among human populations on a world scale is reliably 10 to 15%, kinship between two individuals of the same human population is equivalent to kinship between grandparent and grandchild or between half siblings. The widespread assertion that this is small and insignificant should be reexamined.     

Understanding the demographic implications of climate change: estimates of localized population predictions under future scenarios of sea-level rise

Significant advances have been made to understand the interrelationship between humans and the environment in recent years, yet research has not produced useful localized estimates that link population forecasts to environmental change. Coarse, static population estimates that have little information on projected growth or spatial variability mask substantial impacts of environmental change on especially vulnerable populations. We estimate that 20 million people in the United States will be affected by sea-level rise by 2030 in selected regions that represent a range of sociodemographic characteristics and corresponding risks of vulnerability. Our results show that the impact of sea-level rise extends beyond the directly impacted counties due to migration networks that link inland and coastal areas and their populations. Substantial rates of population growth and migration are serious considerations for developing mitigation, adaptation, and planning strategies, and for future research on the social, demographic, and political dimensions of climate change.     

Habitat fragmentation promotes fluctuating asymmetry but not morphological divergence in two geckos

The process of species formation is often ignored in discussions on the conservation of biodiversity. Yet the clearance of vegetation may promote divergence among populations of a species through isolation, providing conditions for rapid genetic drift and novel selection pressures. Here, stepwise discriminant function analysis and fluctuating asymmetry are used to examine variation in morphology within and among non fragmented and recently fragmented populations of two species of gecko,Oedura reticulata andGehyra variegata. High reclassification error rates using discriminant function analysis, indicate that fragmentation has had no detectable effect on morphological differentiation among populations of either species. In contrast, remnant populations of both species exhibit higher mean levels of fluctuating asymmetry than do populations in undisturbed habitat. ForOedura reticulata, levels of fluctuating asymmetry are negatively correlated with the log of adult population size. These results suggest that the changes following habitat clearance have been severe enough to cause increased developmental instability in populations of both species but not detectable morphological divergence. Given the high rate of extirpation of gecko populations in the study region and the extreme vulnerability of the remaining populations, it is unlikely that species formation will be significant in maintaining reptile diversity in that region.     

Genetic correlation of wing polymorphism between females and males in the oriental chinch bug,Cavelerius saccharivorus Okajima (Heteroptera: Lygaeidae)

Summary Genetic correlations of the wing form and the relative wing length between females and males were estimated in the oriental chinch bug,Cavelerius saccharivorus, by calculating the correlation between the sexes of the proportion macropterous or the mean relative wing length in full-sib families obtained from different wing forms of parents emerged in a high density population. There was a significantly positive genetic correlation between the sexes in both the proportion macropterous and the mean relative wing length. However, the appearance rate of macropters tended to be much lower in males than in females under the rearing conditions which promote the appearance of macropters. This was evident especially in the offspring of brachypterous parents. These indicated that inC. saccharivorus the wing polymorphism of males is not a simple result of the genetic correlation of wing morphology between the two sexes. It was considered that both of the female and male fitness advantages to wing reduction, as well as the genetic correlation between the sexes, would influence the evolution of wing polymorphism in this species.     

Metropolitan migration efficiency

The migration efficiency ratio of an area is defined as the net migration of the area (in-migrants minus out-migrants) divided by the total number of moves whose origin or destination is that area (in-migrants plus out-migrants) multiplied by 100. This paper investigates variations in migration efficiency from 1955 to 1960 among Standard Metropolitan Statistical Areas with populations of 250,000 or more. Regional variation in migration efficiency was evident, ranging from an average of ?9.7 in the Northeast to 19.6 for SMSA’s in the Western region. Nonwhites tended to have higher migration efficiency than whites. Rapidly growing metropolitan areas had higher migration efficiency ratios than areas growing at a lower rate or losing population. The educational level of a metropolitan area, as measured by the percent of the population 25 years old or over with at least a high school education, was positively related to migration efficiency. The composition of the migrant population, both in- and outmigrants for a given area, was related to the value of the migration efficiency ratio. If the migrant population contained a large proportion of persons aged 20–34, migration efficiency was low, regardless of the direction of the major migration stream. Region was found to have a major effect. Variables that had a strong and positive relationship with migration efficiency in one region were usually found to have no relation, or a negative relation, with it in other areas. Obviously, further research is needed for the identification of factors producing these strong regional effects.     

Age structure,growth, attrition and accession: A new synthesis

This paper shows that each equation describing relationships among demographic parameters in a stable population is a special case of a similar and equally simple equation that applies to any closed population and demonstrates some implications of these new equations for demographic theory and practice. Much of formal demography deals with functions that pertain to individuals passing through life, or to a stationary population in which births of individuals are evenly distributed over time. These functions include life expectancy, probabilities of survival, net and gross reproduction rates, expected years spent in various states and the probability that certain events will occur in the course of life. The stable population model permits the translation of population structure or processes in a more general type of population, with constant growth rates, back into equivalent populations for a stationary population. The method for translation developed in this paper, requiring only a set of age-specific growth rates is even more general, applying to any population. Age specific growth rates may also be useful for performing reverse translations, between a population's life table and its birth rate or its age distribution. Tables of numbers of females by single years of age in Sweden are used to illustrate applications. Tables summarize the basic relations among certain functions in a stationary population, a stable population and any population. Applications of new equations, particularly to demographic estimation of mortality, fertility and migration, from incomplete data, are described. Some other applications include; the 2 sex problem, increment decrement tables, convergence of population to its stable form, and cyclical changes in vital rates. Stable population models will continue to demonstrate long term implications of changes in mortality and fertility. However, in demographic estimation and measurement, new procedures will support most of those based on stable assumptions.     

Rapid evolution of larval development time during mass-rearing in the melon fly, Bactrocera cucurbitae

A quantitative genetic analysis of rapid evolution of a life history trait has been conducted on the first 24 generations of mass-rearing in the melon fly Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae). The phenotypic variance of larval development time in each generation was divided into genetic and residual components. Mean and phenotypic coefficients of variation of larval development time decreased gradually as generations proceeded as a result of artificial selection for shorter larval period in the mass-rearing procedure. There was a trend that additive genetic coefficients of variation in larval development time decreased with generations. These changes are entirely attributed to genetic responses to laboratory selection under the mass-rearing environment because the population was maintained at a very large size so as to exclude random genetic drift and inbreeding depression, which would be other factors responsible for the observed genetic changes. The residual coefficients of variation in larval development time did not change with generations. Realized heritability of larval development time was low. The heritabilities for larval development time estimated from parent–offspring regression at generations 60 and 70, when the evolutionary plateau was asymptotically reached, were not significantly larger than 0. Received: April 22, 1999 / Accepted: September 20, 1999     

Intergenerational relations in urban China: Proximity, contact, and help to parents

Although most older Chinese parents live with an adult son or daughter, most adult offspring do not live with parents. We examine the relations of these noncoresident offspring with parents in terms of proximity, frequency of contact, and exchange of help. Based on a 1993 random sample survey conducted in two major Chinese cities, we find that although rates of coresidence are high, noncoresident sons and daughters live close to parents, have frequent contact with their parents, and provide regular help to parents. Relationships with noncoresident sons and daughters are unaffected by whether parents coreside with another child. There is some evidence of closer relationships with sons than with daughters, but parents without a son receive as much help from all children as do parents with sons. The effects of these and other predictors are estimated in multivariate analyses, and results are interpreted in terms of the persistence or change of traditional family norms.     

Elementary models for population growth and distribution analysis

A version of the Lotka-Volterra interaction model is adapted to describe population growth and migration processes in a two-region system. The regions are identified as a metropolis and its non-metropolitan hinterland. Several conditions on growth and migration regimes are imposed. The time behavior of the systems are analyzed, noting especially situations where total depopulation or population explosion eventually occur in one or both populations. Neither growth control nor migration control alone results in a condition of long-run stability in both regions. If at least a momentary condition of zero growth is achieved in both regions, it is possible to maintain finite populations if each population follows a logistic natural growth process and migration flow is proportional to the volume of interaction. It is necessary also that the natural increase limitation is strong relative to migration rates. This result holds even if one population has a net migration advantage over the other.     

Population projections: states, 1995 - 2025

All states will have more people in the future, especially in the south and west, while population aging occurs as the baby boomers age. This report identifies population changes projected to affect the US's 50 states and District of Columbia during 1995-2015. Basic assumptions for state population projections are presented with regard to population, births, deaths, net international migration, and net internal migration. The methodology used to produce the report is also described. Total population and net change is presented in tabular format for each state over the period. These data are used as the basic input to many federal, state, and local projection models which produce detailed statistics on education, economic factors, labor force, health care, voting, and other subjects. State differentials in fertility and mortality are also projected to widen, reflecting the concentration of race and ethnic groups with high fertility in some states and differential migration patterns.