Comparative analysis of population characteristics of the brown planthopper,Nilaparvata lugens st?l, between wet and dry rice cropping seasons in West Java, Indonesia

Summary Population dynamics of the brown planthopper (BPH),Nilaparvata lugens St?l, were investigated in paddy fields in the coastal lowland of West Java, Indonesia, where rice is cultivated twice a year, in the wet and dry cropping seasons. Distinct differences in the basic features of population dynamics were detected between the two rice cropping seasons: (1) In the wet season, BPH populations multiplied rapidly in the period from initial to peak generation, reaching quite often the destructive level despite the low density of initial immigrants. However, in the dry season, the population growth rate and the peak population density were much lower than those in the wet season. The abundance of natural enemies such as arthropod predators played a major role in determining such a difference in seasonal population development. (2) The density at the peak generation or the occurrence of outbreaks in each field was predictable in the wet season with fairly high accuracy on the basis of the density at the initial or previous seasonal generations. In the dry season, however, the rate of population growth and the peak population density widely varied among the fields depending on the water status in each field. (3) Density-dependent processes to regulate the population density were detected in both cropping seasons. In the wet season, the regulatory processes were only detected in such high densities as cause the considerable deterioration of host plants, which suggested that the processes were largely attributable to intra-specific competition. In the dry season, however, the regulatory processes operated at a much lower density in the earlier stages of the crops. The results of an analysis of adult longevity or residence period suggested that the density-dependent dispersal of macropterous adults played an important role in stabilizing the population fluctuation among the fields in the early dry season.     

Ecology of the fiddler crabUca (Thalassuca) vocans vocans (Linnaeus) (Decapoda: Ocypodidae) I. Daily activity in warm and cold seasons

Summary Field observations on the behaviour ofUca (Thalassuca) vocans vocans were made in the estuary of the Okukubi river, Okinawa Island. The formation of the feeding aggregation of wandering individuals or drove was found in warm seasons above an average monthly air temperature 20°C from April to early November, while the aggregation was little observed in cold seasons below the temperature from the middle of November to March. The members of the aggregation tended to move down from the upper levels of burrow area, rather than lower levels. This may be related to the richness of organic matters in the substratum of the lower levels as compared with the upper levels. The feeding aggregation was mostly composed of males, but in June females were numerously seen and its peak occurred in June. It suggested that the peak in June is related to both feeding and copulation. Behaviour different from warm seasons was observed in cold seasons. When feeding on surface soil orEnteromorpha the crabs carried a mass of surface soil or the alga into their burrow. It was though that this behaviour was related to the storage of food. It seems likely that the crabs maintain the population by the formation of the aggregation of wandering feeders in warm seasons when there are no algae and by feeding abundant algae as well as surface soil or by storing up food in good weather for bad one in cold seasons.     

The spatial distribution pattern of the brown planthopperNilaparvata lugens St?l (Homoptera: Delphacidae) in west Java, Indonesia

Summary Spatial distribution pattern of the brown planthopper (BPH) was analyzed at 9 experimental fields in the northern part of West Java during two consecutive rice cropping seasons, i.e., wet and dry seasons. The population of each developmental stage and wing form of BPH at each location showed consistent departure from the random (Poisson) distribution, the variances of the densities in most cases exceeding their means. Namely, the distribution pattern of BPH per hill of rice plant was found to have a general tendency to be aggregated or contagious and to fit fairly well to the negative binomial model. The tendency for aggregation was further confirmed by both the β-values of -m regression being larger than unity and theC _A -values being larger than zero for each developmental stage. Although significant variations in the distribution pattern as measured by β- orC _A -value were observed between different developmental stages, between wing forms and among locations, the degree of aggregation for a given developmental stage at each experimental field remained fairly stable throughout the crop period, despite wide temporal changes in population density. Possible factors to explain these characteristics of the spatial distribution pattern of the BPH in West Java were discussed with reference to the process generating it.     

The impacts of climate variability on household welfare in rural Mexico

In light of the expected increase in weather variability from climate change, we examine the impact of weather shocks, defined as rainfall or growing degree days more than a standard deviation from their respective long-run means, on household consumption per capita. The analyses suggest that both rainfall and temperature shocks affect both food and non-food consumption. Furthermore, the results show that a household’s ability to protect its consumption from weather shocks depends on the climate region and when in the agricultural year the shock occurs. Especially, households in arid climates are not fully protected from weather shocks occurring during the beginning of the wet season (April, May, June). The results highlight the necessity to account for the underlying climatic variation as well as to carefully define the shocks.     

On the stability of the stock-harvesting system controlled by a feedback management procedure

Summary Stability of the stock-harvesting system regulated by a feedback control procedure of catch quota is examined. In the procedure considered, catch quota is changed proportionally to the difference between current and the target stock level (with a proportionality constanth) and to the annual stock growth rate (with a proportionality constantg). Condition for the local stability of the target equilibrium is obtained as a function of the stock-recruitment relation, survival probability of adults, target stock level, time lag before implementation of regulation, age of sexual maturity of the stock, and proportionality constantsg andh. It is shown that, (1) the procedure has the stabilizing effect; it can stabilize the target stock level that is unstable under constant harvest, (2) lower target stock level favors largerg and smallerh, when the target is set around MSYL (the stock level that gives MSY), (3) the degree of stability, measured by the time required to recover the target stock level, is an increasing function of the target stock level, (4) stability and sustainable yield are in trade-off, (5) time delay caused by the time needed before sexual maturity does not affect the stability significantly, but the effect of the time lag before implementation of regulation is significant. Comparison between harvest-control and effort-control procedures is also made, and the advantage of the latter in terms of stability is shown.     

A ten-year study of population dynamics of citrus pests in the pesticide-reduced orchard

Summary To determine the effectiveness of a pest management system that uses pesticides at a low level, we censused populations of seven insect pests and three plant diseases from 1980 to 1989 in a citrus orchard which was managed with a pesticide-reduced and pesticide-free protocols, in Wakayama Prefecture, Japan. In the orchard, we controlled the pests solely by spraying petroleum oil once a year from 1980 to 1985, by not spraying insecticide in 1986, and spraying only germicide in 1987. The arrowhead scale population remained much lower level at which citrus trees begin to wither when petroleum oil was sprayed, whereas it rapidly increased and began to wither trees during the years without spraying petroleum oil. The Indian wax scale population rapidly increased only during a 2-year period and then declined. Although the infection level of the sooty mold was unusually high on the trees where the density of the scale was high, this pathogen did little damage to citrus trees. The population of the red wax scale gradually increased throughout the census period but did not reach the level at which citrus trees begin to be damaged. Other pests also caused negligible damages to citrus trees. The results indicated that the pesticide-reduced pest management system which was proposed by Inoue and Ohgushi (1976, 1977) is valid for the prevention of the outbreak of the arrowhead scale, and that is has the sufficient control efficiency for the other pests in citrus orchards. Contribution to the ecological studies of scale insect 3.     

Preference in flower visits and partitioning in pollen diets of stingless bees in an Asian tropical rain forest

Floral resource partitioning among stingless bees (Trigona, Meliponini, Apidae) in a lowland rain forest in Sarawak, Malaysia, was investigated using tree towers and walkways in a 4-year study that included a general flowering period. We obtained 100 collections of insect visitors to flowers of varying floral location and shape representing 81 plant species. The tendency of 11 species of stingless bees to visit specific flowers with a particular floral location and shape was analyzed by logistic regression analysis. This analysis showed that the proportion of flower visitor collections containing Trigona fuscobalteata and T. melanocephala differed according to floral location. The former was frequently collected at canopy and gap flowers, whereas the latter was most often collected at understory flowers. The analysis also suggested that T. erythrogastra was more rarely collected at shallow flowers than at deep flowers. Analysis of the pollen diets of T. collina, T. fuscobalteata, T. melanocephala, and T. melina revealed that similarity of pollen sources differed among the six permutated pairs of the four species. The lowest mean rank of similarity found was between T. fuscobalteata and T. melanocephala. This result supports the hypothesis that preference in visiting flowers in different locations leads to pollen resource partitioning. Received: May 14, 1997 / Accepted: April 23, 1999     

Rainfall variations and child mortality in the Sahel: results from a comparative event history analysis in Burkina Faso and Mali

Over the last 40 years, the Sahel has seen a long-term downward trend in rainfall. The importance of ecological variables as factors affecting child survival in rural subsistence societies has already been emphasized, but little empirical evidence has been gathered to support this. This paper presents a comparative event history analysis aimed at understanding how rainfall variations may influence child mortality in two neighbouring countries, Burkina Faso and Mali. These countries are similar in terms of population dynamics, economy, livelihood, child mortality and rainfall conditions (i.e. strong south–north decreasing rainfall gradient). Individual data for both countries came from two detailed nationally representative retrospective surveys conducted in 2000. Rainfall data for the 1960–1998 time period were obtained from the Climatic Research Unit. This study shows that child survival in each country is related to specific patterns of rainfall variation across livelihood regions, highlighting the complex nature of environmental causality of child mortality.     

Asset Impacts on Life Satisfaction in an Asset-Rich Country: Focusing on Older Adults in Singapore

Using a representative sample, this study examined the extent to which assets matter for life satisfaction among older adults in Singapore. Singapore is a particularly useful context to explore the relationship between life satisfaction and assets because almost all Singaporeans own their own house, regardless of income level. First, this study used a latent profile analysis to assess patterns of life satisfaction. Then, asset impacts on this pattern of life satisfaction were examined, while controlling for contextual and health factors. The study found that financial assets matter for life satisfaction of older adults in Singapore. In particular, older adults in both the moderate life satisfaction class (LSC) and the High LSC were likely to have higher financial assets. Comparatively, other economic indicators such as real assets, total debts, and monthly household income were not significantly related to life satisfaction of older adults in the Moderate and High LSC compared to the Low LSC. However, real assets and monthly household income were significant predictors distinguishing the Moderate LSC and the High LSC. Throughout the models, total debts were not considered as a significant predictor of life satisfaction differences. This paper concludes by providing several policy and practice implications.     

Climate shocks and migration: an agent-based modeling approach

This is a study of migration responses to climate shocks. We construct an agent-based model that incorporates dynamic linkages between demographic behaviors, such as migration, marriage, and births, and agriculture and land use, which depend on rainfall patterns. The rules and parameterization of our model are empirically derived from qualitative and quantitative analyses of a well-studied demographic field site, Nang Rong district, northeast Thailand. With this model, we simulate patterns of migration under four weather regimes in a rice economy: (1) a reference, “normal” scenario; (2) 7 years of unusually wet weather; (3) 7 years of unusually dry weather; and (4) 7 years of extremely variable weather. Results show relatively small impacts on migration. Experiments with the model show that existing high migration rates and strong selection factors, which are unaffected by climate change, are likely responsible for the weak migration response.     

Anopheles culicifacies giles: Adult ecological parameters measured in rural punjab province, pakistan using capture-mark-release-recapture and dissection methods, with comparative observations onAn. stephensi liston andAn. subpictus grassi

Summary Dispersal, immigration and emigration rates, horizontal and vertical survivorship and absolute population size were estimated for micropopulations ofAn. culicifacies, An. stephensi andAn. subpictus at a series of cattle sheds in rural Punjab Province, Pakistan, during November 1979 and May 1980 using capture-mark-release-recapture and dissection methods. Dispersal was temperature-related, with populations more vagile during May. Mean dispersal distance per individual was low for all species. More than 70% of all recaptures were taken at the point of release and the longest detected flight was 1250 meters. Horizontal survivorship was greater during November and was always less than vertical survivorship calculated from dissection agegrading data. Survivorship during the nulliparous period was greater than survivorship throughout total life, indicating the survivorship curve may be slightly sigmoid. Daily population sizes of endemic and immigrating females and males were calculated usingBailey's (1952) modification of the Lincoln Index, with the daily captures adjusted for immigration which was highest in May. Daily additions to the indoor resting population exclusive of immigrants were estimated using the method ofManly andParr (1968). The relationship of the present findings to malaria transmission and genetic control were discussed.     

Two fish species competition model with nonlinear interactions and equilibrium catches

Summary Two species competition model is built up by assuming the hypothetical second order interactions in order to consider effects of exploitation on two competing fish species with non-linear interactions. Most important characteristic of this model, compared withLotka-Volterra type linear competition model, is that this model can possess multiple stable equilibrium points. Therefore there is a possibility that two species keeping the equilibrium state at one stable equilibrium point will be attracted to the other stable equilibrium point after a heavy perturbation. In this model reversible change of the fishing pressure does not always results in that of the equilibrium catch. In this sence MSY concept for single species can not be extended to this model. If there are multiple stable equilibrium points, the change of the dominant fish species, catastrophic and irreversible change of each equilibrium catch may be observed when the perturbation by the exploitation is added. This phenomenon immediately reminds us of the change of the dominant fish species between Japanese common mackerel and Pacific saury in the northwest Pacific Ocean. In case of the management of two competing fish species with nonlinear interactions, the consideration on the balance between the fishing pressure for each species may be as important as the decision on the catch limit for each species. MSY level for each species based on the single-species theory could be quite erroneous.     

Attitude Toward Menopause and Aging: A Study on Postmenopausal Women of West Bengal

We examined the attitude of postmenopausal women toward menopause and aging with respect to sociodemographic variables and postmenopausal years. Four hundred and eighty postmenopausal women representing Bengali-speaking Hindu ethnic group of West Bengal, India were interviewed about their attitude toward menopause and aging. Information on sociodemographic and reproductive characteristics and menopausal symptoms were also collected. The participants were categorized into four groups based on postmenopausal years (Group 1: ≤2; Group 2: >2 to ≤5; Group 3: >5 to ≤8; and Group 4: >8). The attitude did not differ significantly among different groups, but it differed significantly when compared for residential status and per capita monthly household expenditure (pooled groups), for residential and educational status (Groups 3 and 4), and per capita monthly household expenditure (Group 3). Hierarchical linear regression (stepwise) shows per capita monthly expenditure, age at menopause, years after menopause, and menopausal symptoms (irritability and inability to hold urine) significantly predict attitude.     

Studies on the adult polymorphism in the southern green stink bug,Nezara viridula (hemiptera: Pentatomidae)

Summary Polymorphism in adult colour pattern ofNezara viridula is determined on the genetic basis. The basic colour patterns of adult are classified into four types, i. e. G, O, R and F. No appreciable differences between these types were observed in respect to various physiological traits of nymphs and adults, except that type G seems to be superior in reproductive ability but to be inferior in ability of surviving winters at least to types R and F. Inter-generation changes in percentage frequency of G type were examined from 1959 to 1967 covering more than 30 generations. Percentage frequencies of G types prior to the severe winter of 1962–3 fluctuated greatly around a mean of 87.9%, while they did to a lesser extent than before with a mean of 85.0% after the winter. Unexpected high percentages of G type were recorded frequently in summer generations, viz. 1st and 2nd. On the other hand, the relative frequencies of G and O types decreased after hibernation in contrast to the increases in those of F and R. This sort of changes in genetic composition related to the winter of 1962–3 was observed in several populations segregated from each other. This seasonal alternation of selective activity in the environments is considered to be responsible for retention of the polymorphism. Alternative possible causes, i. e. difference in habitat preference, non-random mating and selective predation by predators among polymorphs, may safely be rejected as irrelevant to the mechanism in maintaining polymorphism. The polymorphism of this insect seems to be in a transient state rather than balanced one contributing little to population regulation, but the persistence ofN. viridula in the periphery range may be assisted by retention of the polymorphism.     

A field experiment on dispersal of newly emerged adults ofMonochamus alternatus (Coleoptera: Cerambycidae)

Summary Newly-emerged adults ofMonochamus alternatus aged 1 to 5 days were code-numbered with lacquer paint and released by placing them on the trunks of one or two trees in aPinus thunbergii stand at weekly intervals during the beetle emergence period from 1980 to 1983. Beetles were captured at weekly intervals from one week after the first day of release. Determinations were made on the distance and direction of beetle dispersal during a week after release and analysed by a method of Inoue (1978). When the stand canopy was closed, the rate of beetle’s stay on trees was 0.56 per week. The beetles dispersed at random by walk and flight. When the pine stand was sparse, the rate of beetle’s stay on trees was 0.02–0.30 per week. They dispersed at random by flight. The average distances traversed were estimated to be 7.1–37.8 m for the first week after emergence. Using other method, the average distance traversed was estimated to be 10–20 m for each week through the first 3 weeks after release. The results of stepwise multiple regression analysis and a simple field experiment suggested that the dispersal of newly-emerged beetles was affected by stand density, number of beetles emerging from individual dead trees, maximum air temperature, and precipitation.     

Sex preferences and fertility in South Korea during the year of the horse

Since antiquity, people in several East Asian countries, such as China, Japan, and South Korea, have believed that a person is destined to possess specific characteristics according to the sign of the zodiac under which he or she was born. South Koreans, in particular, have traditionally considered that the year of the Horse bears inauspicious implications for the birth of daughters. Using monthly longitudinal data at the region level in South Korea between 1970 and 2003, we found that in the year of the Horse, the sex ratio at birth significantly increased while fertility decreased.     

Impacts per unit weight in catch by two types of fisheries on a chub mackerel population

By using data on the age-specific annual fecundity and catches-at-age by each fishery in a chub mackerel (Scomber japonicus) population in the Pacific Ocean off Japan during 1970 to 1992, we evaluated the long-term fluctuation in impacts of two types of fisheries on the chub mackerel population. The purse-seine fishery consistently had a larger impact on the population than did the dip-net fishery, mainly because the catch by the former was much larger than that by the latter. To evaluate impact per unit weight in catch, we calculated the average reproductive value per unit weight over individuals caught by each fishery as an indicator of efficient use of bioresource. Because the proportion of immature fish caught by the purse-seine fishery was usually larger than that by the dip-net fishery, the impact per unit weight in catch by the purse-seine fishery was not always less than that by the dip-net fishery.     

Estimating seasonality effects on child mortality in Matlab,Bangladesh

This paper estimates the net effect of seasonality on child mortality in Matlab. Results suggest that childhood mortality was well above the average monthly level in the hot, dry month of April and in November, the first harvest month of the aman crop. It was found to be remarkably low in the post harvest months of February and March. and also in August. During the hungry months of September and October, children were at a considerably increased risk of mortality. particularly from diarrheal diseases, if mothers had no schooling. but this was not the case if mothers had schooling. The protective effect of the Matlab interventions on childhood death from diarrheal diseases was also greater during the hungry months than during other months of the year.     

Effects of changes in rainfall and temperature on age- and sex-specific patterns of rural-urban migration in sub-Saharan Africa

We evaluate how changes in weather patterns affected rural-urban migration across 41 sub-Saharan African countries, by age and sex, over the 1980–2015 period. We combine recent age- and sex-specific estimates of net rural-urban migration with historical data on rainfall and temperature from the Climate Research Unit (CRU). We also compare standard unweighted estimates of rainfall and temperature to estimates weighted by the proportion of the country’s total rural population in the CRU grid. Results show that rural out-migration of young adults is the most sensitive to shifts in weather patterns, with lower rainfall, lower variability in rainfall, and higher temperatures increasing subsequent rural out-migration—though the last of these is not observed in weighted models. The strength of these effects has grown stronger over time for 20–24 year olds, though weaker above age 30. In contrast, increasing temperature variability is associated with a higher rural in-migration of children (0–9) and older adults (55–64). Gender differences in these effects are minimal and concentrated in areas which experienced heavy reductions in rainfall.

     

A population size estimate of the finless porpoise,Neophocaena phocaenoides, from aerial sighting surveys in Ariake Sound and Tachibana Bay, Japan

We estimated the population size of the finless porpoise (Neophocaena phocaenoides) in Ariake Sound and Tachibana Bay of western Kyushu, southwestern Japan, from aerial sighting surveys using line transect methods. All 12 surveys were conducted from May 1993 to May 1994 (8 in Ariake Sound and 4 in Tachibana Bay). In addition to these, 14 surveys were also carried out to obtain information on porpoise occurrence in Tachibana Bay (5 surveys) and in neighboring Sumo Nada (5) and Yatsushiro Sound (4). In Ariake Sound, 225 porpoise groups (369 animals) were detected during all flights totalling 1,694.4 km. In Tachibana Bay, a total of 997.8 km was surveyed and 55 groups (290 animals) were sighted. However, no sightings were recorded in Sumo Nada (distance searched = 148.7 km) and Yatsushiro Sound (208.4 km). In Ariake Sound, few sightings were recorded from waters shallower than 5 m in depth. In Tachibana Bay all animals were detected from waters of less than 50 m depth. The population size was estimated as 1,983 animals in Ariake Sound (95% CI = 1,382-2,847), 1,110 in Tachibana Bay (95% CI = 642-1,920), and 3,093 in the 2 waters (1.3 individuals/km², 95% CI = 2,278-4,201).