An experimental analysis of the relationship between species combination and community persistence

Among many stabilizing factors for community dynamics, nonlinear biological interactions such as type III functional response have been widely considered to be major characteristics. However, most experimental biological communities employed so far had quite simple structures. Therefore, the possibility that the conclusions in earlier studies were dependent on simple community structure is undeniable. In this study, using a multiple-species experimental community, we evaluated which combinations of component species and what kinds of interspecific interactions allow communities to persist and how these contribute to community persistence. We conducted experimental communities using two species of beans, the adzuki bean (Vigna angularis) and the red kidney bean (Phaseolus vulgaris), two species of bean weevils, the Mexican bean weevil (Zabrotes subfasciatus, Coleoptera: Bruchidae) and adzuki bean weevil (Callosobruchus chinensis, Coleoptera: Bruchidae), and two species of parasitic wasp, Heterospilus prosopidis (Hymenoptera: Braconidae) and Anisopteromalus calandrae (Hymenoptera: Pteromalidae). The outcome of multiple-generation experimental communities was explained by the characteristics of component species obtained from short-term experiments. In our two resources–two herbivores–one carnivore system, the strong density-dependent attack ability of one parasitic wasp species (A. calandrae) led to the extinction of C. chinensis. On the other hand, the weak density-dependent attack ability of the other parasitic wasp species (H. prosopidis) led to system persistence. Our overall results show that, in a multiple-species community, the combination of species itself is more important for community persistence than are the characteristics of the particular species. Received: September 29, 1997 / Accepted: October 5, 1998     

Temporal/spatial structure and the dynamical property of laboratory host-parasitoid systems

The effects of spatial structure in terms of local capacity, or the maximum number of larvae surviving competition at resource patches, and temporal structure in terms of the period vulnerable to parasitoid attack in host populations on the persistence of host-parasitoid systems were quantitatively evaluated by laboratory experiments and well-parameterized model analyses. One of two bruchid beetles,Callosobruchus maculatus andC. phaseoli, were used as a host with Heterospilus prosopidis used as the parasitoid.C. maculatus, in which few larvae survive competition to become adults in each bean, andC. phaseoli, in which many larvae become adults in each bean, along with two kinds of beans, the mung and the azuki, were combined to construct four (2×2) resource-herbivorous host-parasitoid systems that differed in local capacity and vulnerable period. The mung-C. maculatus system with the parasitoid was the most persistent, i.e., took the longest time for extinction of either the host or parasitoid to occur. Since this resource-herbivorous host combination exhibited the lowest local capacity and the shortest vulnerable period, these two conditions possibly promoted the persistence of the system. A model incorporating the host population structure supported the observed persistence. Furthermore, the possible contribution of the timing of density-dependent competition of the host on the host-parasitoid persistence is predicted.     

缺席的在场：失独者生活境况的家庭时空分析与关系性变革

去世的独生子女对于其父母,是一种＂缺席的在场＂,虽然已脱离了其父母、家庭的时间进化过程和生活生产空间,但仍然会以一种特殊的在场方式,影响其父母的行为与行动。基于10户失独者的深度访谈资料,通过构建家庭时空分析的视角,在时间与空间的双维,分析失独者的时间安排与空间生产策略。并于家庭时空之中探讨独子死亡后的家庭链条关系性变革,在此基础上提出对策建议。     

Social Capital and Community Heterogeneity

Recent findings indicate that more pronounced community heterogeneity is associated with lower levels of social capital. These studies, however, concentrate on specific aspects in which people differ (such as income inequality or ethnic diversity). In the present paper, we introduce the number of parties in the local party system as a more encompassing measure of community heterogeneity. This builds on the argument that the number of relevant socio-economic cleavages in the population (i.e. heterogeneity) determines the level of party system fragmentation. Using data on 307 Flemish municipalities, we find that municipalities with a more heterogeneous population indeed have lower levels of social capital. Hence, our study endorses—and generalizes—previous results linking community heterogeneity to lower levels of social capital.

Biodiversity and community structure of temperate butterfly species within a gradient of human disturbance: An analysis based on the concept of generalist vs. Specialist strategies

We monitored nine butterfly communities with varying degrees of human disturbance by conducting a census twice a month during 1980 by the line transect method in and around Tsukuba City, central Japan. We analyzed the biodiversity and community structures using the generalist/specialist concept. The site (community) order based on decreasing human disturbance was positively correlated with butterfly species diversity (H′), species richness (the total number of species), and the number of specialist species in a community, but not with the number of generalist species. The number of generalist species was rather constant, irrespective of the degree of human disturbance. Thus, both the butterfly species diversity and species richness were more dependent on the specialists than the generalists. Our analyses also showed that the generalist species were distributed widely over the communities, and they maintained high population densities, resulting in high rank status in abundance in a community, with more spatial variation in density per species. Specialist species showed the opposite trends. These results demonstrate that the generalist/specialist concept is a powerful tool applicable to analyse the biodiversity and structure of natural communities.     

Identifying population units that comply with capture-recapture assumptions in an open community of alpine grasshoppers

Summary Population units which are homogeneous with respect to capture-recapture assumptions are identified by applying 11 contingency table tests to grasshopper data according to various site, species, growth stage and sex groupings. The results of 2337 contingency table analyses have permitted a definition of the biological, spatial and temporal characteristics of those groupings which were found to be homogeneous. The same analyses suggest that dispersal rates and dispersal patterns pose the greatest single difficulty in defining population homogeneity within an open community. The effects of failures in capture-recapture assumptions are discussed in relation toJolly’s 1965 stochastic model. A more detailed presentation of the study is available from the author on request.     

Community-Based Determinants of Community Engagement: A Meta-Analysis Research

In literature, several variables, both individual and collective level, have been utilized to explain community engagement: the active, voluntary involvement of individuals and groups in changing problematic conditions in communities. The purpose of this study is to identify the main community-based variables and, via meta-analysis research, calculate the effects of these variables on community engagement. These variables include sense of community, community identity, social well-being, place identity, trust in the community, trust in institutions, and community cohesion. The overall and partial effect sizes and heterogeneity between studies were calculated. Some study characteristics (i.e. type of sample, size of sample, percentage of women in the sample, and mean age) were used as moderators for subsample analysis and meta-regressions. The first six major variables (sense of community, community identity, social well-being, place identity, trust in the community, and trust in institutions) show a positive but moderate relationship with community engagement. As for the moderating variables were not found substantial variations. The data are very heterogeneous and highlight the complex and multivariate nature of community engagement. Theoretical and methodological implications were discussed.     

The changing spatial distribution and concentration of Australias chinese and Vietnamese communities: An analysis of 1986–2006 Australian population census data

This paper describes the changing spatial distribution and concentration of Chinese and Vietnamese communities in Australia over the two past decades. The research analyses data of individuals (i) born in the People’s Republic of China or Vietnam, (ii) of Chinese or Vietnamese ancestry, and (iii) who spoke Chinese or Vietnamese languages at home. Basic demographic and economic factors at the SLA level are considered to provide an initial discussion of meso-level factors which may have contributed to changes in Chinese-and Vietnamese-Australian distributions and concentrations since 1986. As expected, from field observations, the data reveal a contrasting picture of the spatial distribution and concentration of the Chinese- and Vietnamese-Australian communities, and indicate that although a few areas of high Vietnamese spatial concentration have persisted into 2006, and a few areas of high’ Chinese spatial concentration have developed since 1986, overall there is an increasing dispersion of both communities into the broader Australian community.     

Social Networks and Unobserved Heterogeneity in Risk for AIDS

As a sexually transmitted disease, AIDS spreads along social networks; consequently,it is reasonable to propose to utilize these networks in teaching people to avoid practices that put them at increased risk of contracting AIDS. Most obviously, homosexual men are both at relatively high risk of contracting AIDS, and in many urban areas have well crystallized community structures and high social connectivity. We present evidence suggesting that using such social networks can have the unanticipated consequence of reaching a set of men who are at relatively low risk. Evidently, there is great unobserved heterogeneity among the population in terms of risk, and while this heterogeneity is not captured by conventional measures of risk behavior, it is closely linked to network processes.     

Dynamics of distribution in animal communities: Theory and analysis

Summary Theoretical and analytical problems of the dynamics of distribution and abundance in animal communities were examined. In many communities, species with low abundance and of limited spatial occurrence (i.e., rare species) typically form a conspicuous peak when a frequency distribution of the number of species is constructed with respect to the proportion of sites occupied within an area of distribution. Models of distribution dynamics, including a new model proposed here, were compared with a range of animal community data using a new procedure to assess single- and bi-modal patterns in frequency distributions of spatial occurrence. Data reveal that single-modality with an excess of rare species occurs more frequently than bimodality. Even when bimodality is detected, the mode representing wide-spread species is in the majority of cases smaller than that for rare species. Thus, a new model in which the rate of local extinctions is assumed to be negatively related to patch occupancy (or population abundance) is in better agreement with observed data than earlier models. Some problems of analysis, in particular model assumptions and testing, are discussed.     

Exploring unobserved heterogeneity in perinatal and neonatal mortality risks: The case of an Italian sharecropping community, 1900–39

Previous researchers have found that traditional determinants explain only a limited part of the variation in perinatal and infant mortality at the family level. In the study reported in this paper, we explored the factors that make the perinatal/neonatal death risk more heterogeneous across families. We estimated logistic regressions with cluster random effects at the maternal level, using data from the Italian village of Granarolo from 1900 to 1939. We estimated the effects of selected predictors on perinatal/neonatal mortality and unexplained inter-family variation. We found that non-rural skilled and lower-skilled workers experienced higher perinatal and neonatal mortality risks. Unexplained heterogeneity at the maternal level was lower for women living in sharecropper families than for those in landless labourer and non-rural worker families. Unexplained perinatal and neonatal mortality components were also due to socio-economic differences and were not necessarily related only to maternal biological features or shared genetic frailty.     

Why is there so much genetic variation for wing dimorphism?

Wing dimorphism appears in general to be determined either by a single locus, 2 allele system in which brachyptery is dominant, or by the additive action of numerous loci. In the latter case studies indicate that the heritability is typically quite large. It is generally postulated that wing dimorphism is under strong selection: why then is genetic variation not eroded? In this paper I consider three possible explanations. First, genetic variation may not be exposed to selection because environmental heterogeneity effectively makes heritability zero. Because wing dimorphisms are known to evolve it seems unlikely that this is the primary factor. Second, directional selection on a threshold trait may push the population almost to monomorphism but erodes genetic variance at a very slow rate. This mechanism cannot preserve variation but makes it possible for other factors to more easily maintain variability. Finally, I demonstrate that in a heterogeneous environment spatio-temporal variation in fitness will itself maintain a genetic polymorphism for wing dimorphism. This paper is dedicated to Professor Sinzo Masaki, whose work on the evolution of wing dimorphism and diapause has been so important to our understanding of the evolution of dimorphic variation.     

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.     

Mortality in late nineteenth-century Montreal: geographic pathways of contagion

In the City of Montreal, 1881, the presence of three cultural communities with different profiles of economic status makes it possible to observe the way social settings affected survival over a lifetime. Regression models show culturally determined maternal factors dominant for infants, and persistent throughout childhood. For post-neonates, children aged 1-4, and adults aged 15-59 household poverty has a comparable effect. Among adults, a gender penalty differs among the three communities. Models are improved when differentiated by cause of death. Locating households using a GIS reveals high levels of residential segregation by ethnicity and income, spatial correlation of environmental hazards, and constraints on exit from zones of risk, which together produce neighbourhood effects as large as household effects. Attention to groups excluded (foundlings and inmates of institutions) confirms that models limited to full household-level information significantly underestimate the impacts of poverty and exclusion.     

A model of the species rank-abundance relation for a community in an open habitat

Summary A mathematical model is proposed to describe the relationship between the abundance and the rank of species in order from the most abundant to the least in a community in an open habitat. This model is derived as a corollary of a species-area equation (Kobayashi, 1975) which could be expected in the case where the individuals of each species are uniformly distributed over a habitat area. Numerical simulation reveals that a rank-abundance curve for a universe results in different species-area or species-individual curves according to the spatial distribution of individuals, and that the relative abundance of each species in a sample varies with sample size unless the spatial distribution of individuals is uniform. A species-individual curve obtained bySanders’s (1968) rarefaction method agrees with that observed actually only for the spatially uniform distribution. Change in the pattern of rank-abundance curve with species diversity and with sample size is discussed in relation to the present model.     

Giving to family versus giving to the community within and across generations

In this paper, we examine the impact of parental giving on the transfer behavior of adult children to family members and community institutions using unique data from the Indonesian Family Life Surveys. Our findings point to persistence of private transfer networks across generations. In particular, the community transfer decisions of adults living outside origin households are positively influenced by the origin household’s community giving. We also investigate the relationship between household transfers to family and community networks. We find that unobserved heterogeneity in giving to family members and community organizations is positively correlated, suggesting important complementarities between transfer networks.     

Increasing Migration,Diverging Communities: Changing Character of Migrant Streams in Rural Thailand

This paper studies how increasing migration changes the character of migrant streams in sending communities. Cumulative causation theory posits that past migration patterns determine future flows, as prior migrants provide resources, influence, or normative pressures that make individuals more likely to migrate. The theory implies exponentially increasing migration flows that are decreasingly selective. Recent research identifies heterogeneity in the cumulative patterns and selectivity of migration in communities. We propose that this heterogeneity may be explained by individuals’ differential access to previously accumulated migration experience. Multi-level, longitudinal data from 22 rural Thai communities allow us to measure the distribution of past experience as a proxy for its accessibility to community members. We find that migration becomes a less-selective process as migration experience accumulates, and migrants become increasingly diverse in socio-demographic characteristics. Yet, selectivity within migrant streams persists if migration experience is not uniformly distributed among, and hence not equally accessible to, all community members. The results confirm that the accumulation and distribution of prior migrants’ experiences distinctly shape future migration flows, and may lead to diverging cumulative patterns in communities over time.     

Predator-prey system structure in patchy and ephemeral phytotelmata: Aquatic communities in small aroid axils

Mechanisms allowing the persistence of an aquatic predator-prey system in tiny pools (the mean ca. 0.5 ml) held by taro axils were analyzed from the viewpoint of temporal and spatial patterns of habitat use. Predatory larvae of a mosquitoTopomyia tipuliformis concentrated in young axils, while 9 other taxa utilized both young and old axils or concentrated more in older axils. The total prey density was lower in axils with the predator but the density of each prey taxon (except for a few cases) and the number of prey taxa did not differ between axils with and without predators. This indicates thatT. tipuliformis is a general predator and does not influence prey community organization through selective removal of particular prey taxa. Inter-axil distribution ofT. tipuliformis was aggregated in the first instar but uniform in the third and fourth instars due to intraspecific cannibalism, which assures the survival of a single individual under short food supply. Distributions of prey taxa were mostly aggregated, fitting the negative binomial distribution. Thirty seven out of 45 associations of 10 taxa were independent with 3 negative (between the predator and some late-colonizing prey) and 5 positive (between some prey taxa) associations. Probabilistic refuges (produced by independent aggregated distributions) reduced interspecific encounters which may result in competition and predation, and thus probably facilitated prey coexistence. There was no evidence for the importance of predation in structuring the prey community. This system may be prey-dominated in that predator persistence depends on prey community existence but prey community structure depends less on predation.     

Habitat stability and the larval mosquito community in treeholes and other containers on a temperate Island

The temporal fluctuation of water levels and the presence of mosquito larvae were investigated for four types of small container habitats (treeholes, bamboo stumps, cemetery stone vases, and cemetery stone vessels) on Kabeshima Island in Kyushu, southwestern Japan. The probability that containers held water was positively correlated with the quantity of the preceding rainfall and with the depth and volume of the containers. It was estimated that dehydration occurred more regularly in autumn and winter than in summer. The probability that mosquito larvae were present in each type of container was positively correlated with habitat stability in terms of the probability of the existence of standing water and the coefficient of variation of the water level. Twelve species of mosquito larvae, including two rare predators, were found. Species composition differed between the different types of container. Although 4 to 10 species used each type of container, the median number of species per container was two for treeholes and bamboo stumps, and one for the others. The dominant species wasTripteroides bambusa in treeholes and bamboo stumps,Aedes albopictus in stone vases, andA. japonicus in stone vessels. The larval mosquito community, which lacked major predators, possessed the following features that may facilitate the coexistence of many species: (1) niche segregation amongst species in terms of their selection of container types; (2) an aggregated distribution of the individual species among containers of the same type; (3) high intraspecific mean crowding (and hence probably intense intraspecific competition) in the dominant species in each type of container; (4) independent species associations within the same type of container; and (5) low interspecific mean crowding (and hence probablynot intense interspecific competition) between species in the same type of container.     

Species diversity preserved in different numbers of nature reserves of the same total area

Conclusion and Summary The expected number of species occurring in different numbers of reserves of the same total area is examined on different assumptions of the spatial distribution and the probability of extinction. The advantage of one large reserve or several smaller ones of equal total area depends on the spatial distributions of species and the stage after the establishement of reserves. In general, several smaller reserves maintain more species immediately after the establishments unless the spatial distribution are uniform or random, whereas one large reserve excels several smaller ones after some rare species have gone extinct unless the spatial distributions are strongly contagious. Since the extinction of rare species must be facilitated as the size of each reserve reduces, the area of a reserve should be larger than the critical area that ensures the persistence of the species. Hence it is concluded that one or a few large reserves are a better strategy in order to maintain the species diversity.