Aggregation pattern of individuals and the outcomes of competition within and between species: Differential equation models

Summary The influence of spatial distribution pattern on the outcomes of intra- and interspecific competition is studied theoretically. The models developed are the generalized logistic andVolterra equations, whereLloyd’s indices of intra- and interspecies mean crowding were incorporated with their assumed linear relationship to mean density in order to express the intensity of crowding which is really effective to the existing individuals. It is shown that while the increasing patchiness of distribution has a pronounced effect of promoting the intraspecific competition and lowering the equilibrium density for individual populations, it generally relaxes the interspecific competition, making it easy for different species sharing the same niche, which would otherwise be incompatible, to coexist stably. These models thus provide a simplest theoretical basis to explain why many insect populations in nature are kept relatively rare in number and why a number of allied species often coexist freely sharing the same resource, against the “competitive exclusion principle” deduced from the originalVolterra equations.     

Conceptual dimensions of crowding reconsidered

A recent and noteworthy facet of crowding research has been the exploration of the perception of high density/crowding experiences. A review of the methods and results of these investigations reveals considerable variation across studies on the dimensions of stimulus domain and selection, attention to intersubject differences, and approaches to interpreting results. The outputs of these studies do not appear as clearcut as has been suggested. It is hoped that the raising of these issues will result in more careful and fruitful research in this area. The links between conceptual crowding, situational variables, intrapersonal variables, and behavioral responses to high density/crowding are discussed.     

Density,Crowding, and Factors Intervening in Their Relationship: Evidence from a Hyper-dense Metropolis

This paper, using survey data from 414 urban residents in Hong Kong, examines the effects of space, achieved privacy and satisfaction with living quarters on the perception of crowding. The results of this study suggest that occupants of spatial constrained dwellings do not necessarily feel crowded. While achieved privacy intervenes in the relationship between space and crowding, its effect is indirect and very moderate. Instead, the dissatisfaction with physical environment rather than with a quantity of space itself is a major cause of the feeling of crowdedness. These findings imply that architectural designs that meet the expectation of occupants may well alleviate feelings of crowdedness in situations of spatial constraint.     

Spatial distribution and mortality process ofAnoplophora malasiaca (Coleoptera: Cerambycidae) eggs in citrus groves

Summary The study was carried out in two (A and B) citrus groves to clarify the spatial distribution patterns of eggs and larvae, and to analyse the mortality process of eggs. From the analysis by using the mean density and the mean crowding, it was clarified that the distributions of eggs were contagious and that larvae were more contagiously distributed than eggs. The τ andz indices showed that the operation of egg mortality was inversely density-dependent in both groves, and that the degree of inverse density-dependence was greater in A than in B grove. The spatial correlations between the emergence holes and the eggs or larvae in each tree, which were analysed by using ω index, showed that the distributions were more overlapping between the emergence holes and the larvae than the eggs. As the result of dividing trees into several groups according to the number of emergence holes, it was clarified that the survival rates of eggs were positively correlated with the number of emergence holes. In conclusion, inversely density-dependent mortality process was considered to be caused by lower mortality rates of eggs in the trees with more emergence holes. Especially in A grove, because the trees with more emergence holes were larger in diameter and more egg oviposition, the inversely density-dependent mortality process was considered to be detected more conspicuously than in B grove.     

Use of the regression of mean crowding on mean density for estimating sample size and the transformation of data for the analysis of variance

Summary An approximate method for estimating the sample size in simple random sampling and a systematic way of transformation of sample data are derived by using the parameters α and β of the regression of mean crowding on mean density in the spatial distribution per quadrat of animal populations (Iwao, 1968). If the values of α and β have been known for the species concerned, the sample size needed to attain a desired precision can be estimated by simply knowing the approximate level of mean density of the population to be sampled. Also, an appropriate variance stabilizing transformation of sample data can be obtained by the method given here without restrictions on the distribution pattern of the frequency counts. Contribution from the Entomological Laboratory, Kyoto University No. 418. Contributions from JIBP-PT No. 52. Aided in part by a grant from the Ministry of Education for the special project research, ‘Studies on the dynamic status of biosphere’.     

Analyses of spatial patterns and population processes of clonal plants

The nonrandom spatial structure of terrestrial plants is formed by ecological interactions and reproduction with a limited dispersal range, and in turn this may strongly affect population dynamics and population genetics. The traditional method of modelling in population ecology is either to neglect spatial pattern (e.g. in transition matrix models) or to do straightforward computer simulation. We review here three analytical mothods to deal with plant populations in a lattice-structured habitat, which propagate both by seeds that scatter over the whole habitat and by vegetative reproduction (producing runners, rhizomes, etc.) to neighboring vacant sites. [1]Dynamics of global and local densities: Dynamical equations of population density considering nearest-neighbor correlation (spatial clumping) are developed as the joint dynamics of global average density and local density (comparable to mean crowding) based onpair approximation. If there is a linear trade-off between seed production and vegetative reproduction, the equilibrium abundance of the population may be maximized by engaging both means of reproduction. This result is accurately predicted by the pair approximation method, but not by mean-field approximation (neglect of spatial structure). [2]Cluster size distributions: Using global and local densities obtained by pair approximation, we predicted cluster size distribution, i.e. the number of clusters of occupied sites of various sizes. [3]Clonal identity probability decreasing with distance: Multi-locus measurement of allozymes or other neutral molecular markers tells us whether or not a given pair of individuals belong to the same clone. From the pattern of clonal identity probability decreasing with the distance between ramets, we can estimate the relative importance of two modes of reproduction: vegetative propagation and sexual seed production.     

Residential satisfaction as an intervening variable in residential mobility

The stress-threshold model (Wolpert, 1965; Brown and Moore, 1970) assumes that people do not consider moving unless they experience residential stress. This paper develops a similar model of residential mobility in which residential satisfaction acts as an intervening variable between individual and residence variables and mobility. The model is tested with data from a panel study of Rhode Island residents. The results indicate that residential satisfaction at the first interview is related to the wish to move and to mobility in the year following the interview. Individual and residence characteristics such as age of head duration of residence, home ownership, and room crowding are shown to affect mobility through their effect on residential satisfaction.     

Stabilization effects of spatial aggregation of vectors in plant disease systems

Stabilization effects of spatial aggregation of vectors were examined in insect-borne plant disease systems by constructing a model that describes the yearly dynamics of rice stripe virus disease transmitted by the small brown planthopperLaodelphax striatellus (Fallén). Two transmission paths between vectors were considered: vertical transmission from parents through eggs, and horizontal transmission from infected plants by acquisition feeding. In this model, a paddy field was divided into quadrats and horizontal transmission was assumed to occur within each quadrat. A negative binomial distribution was used to describe the frequency distribution of vectors per quadrat. The parameters of the model were estimated using field data collected in Ibaraki Prefecture, Japan. The model showed that (1) the disease cannot invade into an epidemiological system if the mean crowding of vectors is less than a critical value, (2) the proportion of infected vectors is maintained at about 30% irrespective of the vector density if vectors are highly aggregated, and (3) the proportion of infected plants is maintained at a low level irrespective of the vector density if vectors are highly aggregated. It was also shown that these stabilization effects of aggregation in this epidemiological system come from a mechanism that is common to other systems such as single-species systems and competition systems.     

Crowding and reactions to uncontrollable events

The current study sought to test the consequences associated with misattributing uncontrollable events to crowding. Results showed that when density is a salient cue, greater crowding attributions were made when individuals were exposed to uncontrollable as opposed to controllable outcomes. In addition, performance deficits were found for individuals who were exposed to uncontrollable outcomes, indicated high crowding, and were administered a subsequent task in a nondense setting. The results are discussed in relation to the learned helplessness model as well as studies investigating the aftereffects of stress on human performance.The authors would like to thank Claude Steele for his comments on an earlier draft. Requests for reprints should be sent to David Kuykendall, Department of Psychology, NI-25, University of Washington, Seattle, WA, 98195.     

Analysis of spatial association between two species based on the interspecies mean crowding

Summary and Conclusion The measurement of spatial association between two species is considered on the basis of interspecies mean crowding. Two indices of overlapping, γ andC _p, are derived as geometric and weighted arithmetic means of the same component ratios related to inter-and intraspecies mean crowdings. Both indices behave in a similar way, ranging from 1 when the distributions of two species are completely overlapped to 0 when they are completely exclusive with each other. The former is essentially identical with indices proposed byKuno (1968) andPianka (1973), and the latter is a modified form ofMorisita's (1959)C _σ index. Indices to measure the degree of spatial correlation between species, Ω andR _μ, are then derived for both kinds of overlapping indices, which vary from 1 in complete overlapping, through 0 in independent occurrence, to −1 in complete exclusion. Various kinds of interspecies association are analyzed using these indices and an extended form of the regression graph which provides a convenient way of indicating the spatial interrelation between two species as well as distribution patterns of respective species. The method presented in this paper may also be applicable to compare temporal distribution patterns between species, similarity between communities, etc. For such a wider application which includes continuous as well as discrete distributions, the interpretation of intra-and interspecies mean crowdings is not necessarily appropriate, and hence the concept of mean concentration with the symbols and for intraspecies relation and and for interspecies relation is suggested. This study was supported by Science Research Fund (No. 148041) from the Ministry of Education.     

Pit-relocation of antlion larvae in relation to their density

Of the biotic factors potentially affecting the foraging behavior of pit-building antlion larvae,Myrmeleon bore Tjeder, we focussed on the density effects and examined experimentally influences of larval density on pit construction behavior, spatial distribution and pit relocation rate. Moreover the mechanism of mutual interference among larvae was examined.

Analysis of contagiousness in the action of mortality factors on the western tent caterpillar population by using the \mathop m* - m\mathop m\limits^* - m relationshiprelationship

Summary The contagiousness in the operation of mortality processes on the colonies of the western tent caterpillar,Malacosoma californicum pluviale, was analyzed from two different aspects: successive changes in the frequency distribution of the number of surviving individuals per colony in the course of development, and the distribution pattern of the individuals killed by some biotic mortality factors. Also, for a tachinid parasite,Tachinomyia similis, the analysis was made on the egg-laying pattern on colonies as well as on individual larvae. The methods of these analyses were all based on the relation of mean crowding (m) on mean . A braconid parasite,Rogas sp., tended to kill few individuals together once it attacked a colony, but its effect on host colonies was rather equivalent to the random removal of individuals from all the colonies. Diseases in the late-stage larvae before cocooning was contagious in their action. Nuclear polyhedrosis virus seemed to have no basic contagiousness in its action, but it caused highly contagious distribution of deaths among the colonies when its average incidence was high. A spore-formingBacillus had a tendency to kill several individuals once it appeared in a colony, but the distribution of its incidence (no. of times it appeared per colony) was considered to be nearly at random. The female ofTachinomyia tended to lay more than one egg successively on the same colony. It also attacked individual larvae with a definite tendency for aggregation, which seemed to be resulted from the parasite’s preference to large hosts. When the number of eggs laid on prefered hosts exceeded a certain threshold, however, the fly seemed to change its attention to less attractive, smaller individuals.     

High Levels of Same-Sex Experiences in the Netherlands: Prevalences of Same-Sex Experiences in Historical and International Perspective

Some authors suggest that the public stance toward homosexuality can influence the prevalence of same-sex experiences (e.g., Butler, 2005 Butler, A. C. 2005. Gender differences in the prevalence of same-sex partnering: 1988–2002. Social Forces,, 84(1): 421–449. [Crossref], [Web of Science ®] , [Google Scholar]). Since the Dutch stance toward homosexuality has become more positive during the last decades, it was hypothesized that the current Dutch prevalences of same-sex experiences are higher than in other times and countries. This hypothesis was investigated using the data of a recent Dutch population study, and comparing these results to those from previous and international studies. The current Dutch figures were indeed higher than recent figures from other countries. Among women, the recent figures were also higher than those found in previous Dutch studies. The prevalence of same-sex experiences among Dutch males stayed the same. These results and the methodological aspects of the study are discussed.     

Dispersion analyses and resource utilization of aphid parasitoids in a non-depletable environment

Summary Dispersions and resource utilization of primary and secondary parasitoids developing in non-depletable primary host populations were determined for an aphid-parasitoid community occurring on strawberries. Analyses of dispersions based onGreen's coefficient andLloyd's Patchiness Index indicated parasitized aphids were highly aggregated initially, became less aggregated as density increased, and remained aggregated following collapse of the aphid populations. The “index of aggregation” values calculated usingTaylor's Power Law concurred with results from the other indices, and the similarity of the regression coefficients from both seasons suggests that the index of aggregation may be characteristic for communities as well as species. Analysis withIwao's regression of mean crowding on the mean generated similar results when population data were stratified temporally, and also indicated that the individual was the basic unit of the population. In a non-depletable environment, oviposition of individuals exhibiting an aggregated dispersion pattern within clumps of hosts provides primary parasitoids with a suitable trade-off between energy utilization or genetic potential, and losses associated with hyperparasitism.     

Why people feel crowded: An examination of objective and subjective crowding

Prior studies have found only a modest relationship between objective and subjective crowding, defying logic and commonsensical notions of why people feel crowded. Using data from a representative sample of Bangkok, Thailand, where the level of household crowding is four times that in western societies, we explore several possibilities of why this is the case. Examining seven different indicators of objective crowding, our analyses suggest that the modest relationship is not an artifact of measurement. Contrary to the assumption of prior investigations, the findings indicate that the objective-subjective crowding relationship is nonlinear and that there is a ceiling effect muting the impact of increased objective crowding. The analyses further suggest that the strength of the relationship is mitigated somewhat, with part of the feeling of being crowded accounted for by household circumstances, such as the degree of control an individual has over the use of household space.     

Modelling the effects of population aggregation on the efficiency of insect pest control

Summary A methodology is developed to assess the effects of spatial distribution on the efficiency of insect pest control. This methodology is especially applicable to pest control methods whose efficiency of action depends either positively or negatively on pest density It is applied here to the sterile insect technique and pheromone trapping for male annihilation, which both depend negatively on density. This methodology relies on quantifying clumps of various size and then relating this to efficiency of control and predicting the total pest production given the information on clump sizes and efficiency of control for each clump size. It is found that control is about four times as difficult for a population that is highly clumped (k of the negative binomial distribution=0.25) as for a regularly dispersed population.     

Population dynamics of the whitebacked planthopper,Sogatella furcifera (Hemiptera: Delphacidae) with special reference to the relationship between its population growth and the growth stage of rice plants

A population census was conducted to describe the effects of the growth stage of rice on the population dynamics ofS. furcifera, in particular, on immigration, seasonal abundance, population growth rate, and wing-form expression. The number of immigrants was highest on rice plants 17 to 30 days after transplanting (DAT), which suggested that immigrants prefer to settle or remain more on rice plants at the tillering stage (approximately 20–30 DAT). Population growth rate from immigration to the 1st generation decreased with an increase in rice plant age. In contrast, population growth rate from the 1st to 2nd generation was not influenced by rice plant age and was negatively density-dependent. The percentage of macropters (flyers) was positively related to the growth stage of rice when rice was in the vegetative or early part of the reproductive stage, and reached 100% at about 10 days before heading (booting stage). Threafter, most adult females molted into macropters regardless of population density. The roles of host plant age and crowding effect on the population dynamics ofS. furcifera are discussed.     

生命历程视角下农民工留城与返乡意愿研究——基于重庆和珠三角地区的调查

本研究从生命历程的视角出发,利用2010年"农民工社会适应问题研究"课题组在重庆和珠三角地区所收集的调查数据,分析了影响农民工留城与返乡意愿的影响因素。研究发现,除了个体的能动性如教育程度和收入水平会影响其留城意愿外,与生命历程相关的出生组效应、家庭所处的生命周期以及一定的空间效应都会影响农民工的留城和返乡意愿,另外,性别因素也会导致其留城意愿的差异,文化方面的适应也会极大地影响农民工的留城意愿。     

Employment transitions in the Netherlands, 1980–2004: Are low educated men subject to structural or cyclical crowding out?

This article addresses whether low educated men are displaced from their jobs by higher educated workers in the Netherlands in the period 1980–2004. In particular, we test whether structural or cyclical crowding out is predominant in the Dutch labor market. In order to do so, we try to explain the observed trends in education-specific transition rates to entry into first employment from education, exit from employment into unemployment or inactivity, and re-entry into employment from unemployment or inactivity for men by both business cycle effects (that is, changes in aggregate unemployment rates) and structural effects (that is, changes in labor supply–demand ratios for high educated). Discrete-time event history models are estimated using the OSA Labor Supply Panel 1985–2004. Retrospective information enables to study trends from 1980 onwards, so that structural effects can be distinguished from cyclical effects. The results show that structural crowding out exists at both the worker in- and outflow. First of all, it was observed that a growth in the oversupply of high educated increases the employment exit risk of low educated workers more so than that of higher educated ones. In addition, it was shown that an increase in the oversupply of high educated especially reduces the re-employment chances of low educated unemployed men. There is no evidence found for cyclical crowding out among low educated workers in the Dutch labor market.