The ingestion in wolf spiders II. The expression of degree of hunger and amount of ingestion in relation to spider's hunger

Summary To express the degree of hunger during both of feeding and unfeeding periods of spiders, equations for the amount of ingestion and food disappearance from the gut were presented using three components: capacity of gut, rate of ingestion and rate of food disappearance. The degree of hunger was expressed by the rate of unfilled capacity of gut to the capacity of gut based on these equations. The rates of ingestion and food disappearance were estimated from the results of experiment with a wolf spider,Pardosa laura. The equations obtained well applied to the experimental result. By changing values of these rates, it was revealed that the ratio of rates of ingestion to food disappearance determine the amount of ingestion.     

Comparison of male adult population densities of the oriental and artocarpus fruit flies,Dacus spp. (Diptera: Tephritidae), in two nearby villages in Penang, Malaysia

Summary The populations of native male adult oriental fruit flyDacus dorsalis (Hendel) and artocarpus fruit flyD. umbrosus (F.) in two selected site (BU and SD) were estimated weekly by the capture-recapture technique using live traps baited with methyl eugenol. In BU where many varieties of fruit trees were grown, the estimated population densities ofD. dorsalis were between 980 and 3100 male flies per ha between May and July, 1984. During the same period, in SD where there were fewer number and varieties of fruit trees, the estimated population densities were between 300 and 1000 flies per ha. The estimated population densities ofD. umbrosus over the same period were between 570 and 1290 flies per ha in BU; and between 5 and 95 flies per ha in SD. Of a total 6828 markedD. dorsalis flies released only one fly (released 6 weeks earlier in BU) was caught in a different site.     

Variability in food consumption rate of natural populations in the spider,Nephila clavata

Summary Mean daily food consumption and total lifetime food consumption of the spider,Nephila clavata, were estimated in natural populations. Daily food consumption in the late adult stage was 27–150 mg wet weight, which was nearly equivalent or slightly larger than that in other large web-building spiders. Considerable variation in food consumption was found among habitats or years. The largest variation among habitats in the same year was 7 and 5 fold for daily and lifetime consumption, respectively, while that among years in the same habitat was 3.5 and 2.5 for daily and lifetime consumption, respectively. Feeding conditions evaluated from the food consumption per body weight of spiders declined during the period from mid-July to mid-September in almost all the populations, which suggested that they faced to severe food limitation in this period.     

Decrease in respiratory rate in a wolf spider,Pardosa astrigera (L. Koch), under starvation

Summary Effects of starvation on the suryival period and the respiratory rate in adults of a wolf spider,Pardosa astrigera (L. Koch), were investigated. The spiders used were divided into four groups: well-fed, starved and two limited food groups; in the latter two, each spider was supplied with one leafhopper every second or third day. Adult males and females ofP. astrigera could survive for a long time; 28.8±2.7 days and 54.4±18.9 days, respectively, without any food. The longevities shown here were 73.8% for males and 78.6% for females of those of well-fed spiders, indicating thatP. astrigera adults have a strong tolerance to starvation. The respiratory rate of well-fed adults showed no tendency to increase or decrease with their aging; the mean respiratory rates were 4.86×10⁻⁴ mg CO₂/mg f.w. (fresh body weight)/hr for males and 3.80×10⁻⁴ mg CO₂/mg f.w./hr for females. The respiratory rates of starved spiders increased during the first two days of starvation but decreased markedly from the third to the twelfth day, and thereafter retained an almost constant level for each sex. The mean respiratory rates after the twelfth day of starvation were 2.49×10⁻⁴ mg CO₂/mg f.w./hr for males and 2.76×10⁻⁴ mg CO₂/mg f.w./hr for females; these values were respectively 48.4% and 63.0% of those prior to starvation. The fresh body weight of starved spiders decreased linearly with time but the rate was small. The respiratory rates of the limited food groups tended to decline with time and thereby their weight losses were minimized. The decrease in the respiratory rate under starvation was considered not to be due to spider exhaustion or senescence but due to an intrinsic change in behaviour and/or metabolism, because when the spiders were supplied with ample food for five days after starvation, the respiratory rate and the body weight rapidly recovered to near the levels prior to starvation. It is suggested that starved spiders use a higher ratio of fat as catabolic substrate than normally fed or satiated ones. Feeding strategies of poikilo-therm predators are discussed. This work was partially supported by the Nippon Life Insurance Foundation Research Fund and Grant-in-Aid (No. 56480039) from the Ministry of Education, Science and Culture, Japan.     

The role of the brown-eared bulbulHypsypetes amaurotis as a seed dispersal agent

The role of the brown-eared bulbul,Hypsypetes amaurotis, as a dispersal agent for seeds of fruiting plants was studied by field observations for two years, in parallel with laboratory experiments on seed germination. Bulbuls consumed fruits of 53 species from 24 plant families. The fruits of these plants had similar color and size, and these characteristics were likely to enhance the feeding efficiency of the frugivore. Laboratory experiments on 20 food plant species demonstrated that: (1) no seeds were injured by passing through the bulbul's gut; (2) seeds that had passed through the bulbul's gut were still able to germinate and (3) fruit pulp reduced germination ability. When pulp was removed by passing through bulbul's gut, or by hand, germination was improved. An estimate of the home range of six bulbuls suggested that they may transport seeds for at least 300 m.     

Relationships between body size, reproductive traits, and food resource in three species of tropical flesh flies

Summary Intra- and inter-specific comparisons in progeny size and clutch size were used to identify possible selection pressures acting on three sympatric species of ovoviviporous flesh flies. Both progeny and clutch sizes increased with body weight of the female parent in all species. There was no evidence for a simple trade-off between the two traits. In one species, the larger the female adult the smaller the relative biomass of larvae per clutch (total weight of larvae/body weight of female parent). Female flies produced similar progeny and clutch sizes over successive batches. Variation in progeny size did not influence either larval survival or duration of larval and pupal development. However, larger first instar larvae tended to form larger pupae in two of the species. The experiments testing the effect of progeny size on pupal weight under limited food conditions suggest a selective advantage for larger progeny size.     

Variations in carambola infestation rates byBactrocera carambolae drew and hancock (Diptera: Tephritidae) with fruit availability in a carambola orchard

The relationship between the infestation rate of carambola fruits byBactrocera carambolae Drew and Hancock was investigated in a carambola orchard. Phenology of the fruits was found to influence percentage infestation of fruits byB. carambolae. The proportion of unbagged or susceptible fruits infested varied with time of year and tended to decrease with the increase of unbagged fruits available on the tree. The number of ovipunctures per fruit varied with fruit size and was also found to be indicative of the number of adult insects (B. carambolae and parasitoids) that will emerge from each fruit. Higher number of susceptible fruits available on each tree also decreased both the number of ovipunctures per fruit and the number of eggs laid per fruit, which could possibly be due to the strategy of spreading the risk adopted by the femaleB. carambolae or a result of random selection with more hosts available. The main parasitoids recorded wereBiosteres vandenboschi (Fullaway) andB. arisanus (Sonan). The mean percentage of parasitism was 38.3% and it followed roughly that of infestation of fruits.     

Food limitation of population density in the orb-wed spider,Nephila clavata

Summary Field studies were conducted to clarify whether variation in food availability among habitats influences population density, and whether population density has a negative effect on foraging success in the orb-web spider,Nephila clavata. Lifetime food consumption per individual (i.e., foraging success) strongly correlated with mean body size of adult females and mean fecundity in populations. Also, there was a positive correlation between foraging success and population density. Since foraging success reflected potential prey availability in the habitat, food resource appeared to be a limiting factor for populations in this spider. Mean fecundity per individual correlated with population density of the following year, suggesting that decreased reproduction is a major component of food limitation on population density. Consistent defferences in mean body size between particular sites were observed over years, while such difference was less obvious in density. Thus, ranking of food abundance among habitats seems to be predictable between years. A field experiment revealed that an artificial increase in population density had no negative effect on the feeding rate of individuals, suggesting that intraspecific competition for food is not important in this species.     

Selection for divergent emigration rates in laboratory populations ofMusca domestica

Summary High and low emigration rates through a laboratory system were selected for in populations of house flies (Musca domestica L.). Emigration consisted of movement of flies from on plastic box to another by way of a connecting tube. Selection was carried out by first dividing a wild population of flies into two lines and then selecting for movement from the box in one line and against movement from the box in the other line. The selection experiment was performed twice. In both experiments a statistically significant difference between the two strains was obtained in three to four generations of selection. In the second experiment, after 5 genrations the mean number of high emigration rate flies emigrating in 1 hour was 4.37 times the mean number of low emigration rate flies and in 24 hours was 2.81 times the number of low emigration rate flies. The second experiment was terminated after 6 generations, but the first experiment was continued for 35 generations. In this case, divergence ceased in roughly 15 generations. The possible relevance of the findings to laboratory population experiments in which spatial discontinuities are included is discussed. This study was supported by a research grant of the National Science Foundation (Environmental Biology GB 4567) to Prof. DavidPimentel. The author wishes to thank Prof.Pimentel for his aid and encouragement.     

A laboratory study on the predatory miteTyphlodromus pyri (Acarina: Phytoseiidae): I. The effect of temperature and food consumption on the rate of development of the eggs and immature stages

Summary Development periods were determined for eggs and juvenile stages of the predatory phytoseiid miteTyphlodromus pyri at four constant temperatures and three feeding levels. For the non-feeding stages (eggs and larvae) power curve functions were fitted to development rate in terms of temperature. The results are compared to the general arthropod response to temperature. A non-linear model was fitted to nymphal development rate in terns of temperature and food, in which the weight gain over an instar is assumed to be a linear function of daily food consumption. Examples of the same shape development rate—food relationship are given for two more phytoseiid mites and for other arthropods. The results are discussed with respect toT. pyri as an integrated control agent.     

Pollination and factors limiting fruit set of chasmogamous flowers of an amphicapric annual,Polygonum thunbergii (Polygonaceae)

Summary We observed phenology and insect visitors of chasmogamous flowers of an amphicarpic annual,Polygonum thunbergii (Polygonaceae) in Kyoto, Japan, and clarified limiting factors for fruit set by bagging and hand-pollination experiments. Flowering season was one month from late September. Flowers were visited by various insect groups (total 30 families and 64 species) and effective pollinators were lower bees (Halictidae) and wasps (Vespidae) in the early flowering season, and middle-sized flies (Syrphidae and Calliphoridae) in the later season. Nectar was secreted at a constant rate (0.013mg sugar/hour) throughout a day and >90% of it was consumed by insects. The average number of flowers per ramet was 122, of which 95% were pollinated in the natural conditions. Bagging experiments showed that 47% of flowers were self-pollinated even under no pollinator visits. Despite of a high probability of cross pollination, the probability of fruit set within the ramet was 0.30 due to resource limitation. We discussed possible adaptive significance of cleistogamous flowers under the condition that seeds could be produced by chasmogamous flowers through self-pollination even under pollinator limited conditions.     

A mathematical model of the food-consumer system I. A case without food replenishment

Summary A simple mathematical model was proposed to describe the dynamics of a food-consumer system. The model was based on the Logistic Theory and consisted of Eqs. (4), (5) and (6). The model was divided into the following three cases for further analyss; i) without food supply except at the initial time, ii) with continuous food supply at a constant rate, and iii) with food supply at varying rates. Only the first model was dealth with in this paper. The assumptions of the model 1 are that a definite amount of food is given only once at the initial time and only the feeding by animals is responsible for the decrease of food, and that the rate of decrease is proportional to the amount of animals. It is also assumed that the growth of animal population is represented by the logistic curve, and that the upper limit of the population is proportional to the amount of food at that time. For simplicity the parameters of basic differential equations are assumed to be constant throughout the time course. Analytical solutions of this non-linear model were given by Eqs. (8), (9), (10) and (11). The properties of time course of the food amount and consumer population were discussed from the mathematical and biological points of view. The method of the estimation of the three constants λ,b, andc from the experimental data was also suggested. Since we had no available data for animal populations, we applied the model, regarding reserve substance asx and new plant body asy, to the data of the initial growth of Azuki bean plant in the dark. This model is very simple, but it may be useful for analyzing the behavior of food-consumer system. And it may give some clue to the analysis of the more complex systems.     

Human Carrying Capacity Is Determined by Food Availability

Simple mathematical models have illustrated the relationship between human carrying capacity and population growth. In this study, food supply is proposed as the variable which best accounts for the human carrying capacity. The logistic equation, using food supply data as a variable carrying capacity, yields population estimates which are in accord with actual population numbers. That food supply data adequately fits the logistic model of human population dynamics provides evidence that, consistent with ecological notions typically applied only to nonhuman species, human population increases are a function of increased food availability.     

Modelling Deceleration in Senescent Mortality

Mortality deceleration is the observed but yet to be understood phenomenon that the increase in the late-life death rate slows down after a certain species-related advanced age. Various definitions of onsets of mortality deceleration are examined. A new distribution based on the Strehler-Mildvan theory of aging takes on the required shapes. The application is done on mortality data from the 1892 cohort of Swedish women and on Mediterranean fruit flies.     

What demographers can learn from fruit fly actuarial models and biology

Historically demographers have viewed the results of actuarial studies of nonhuman species, particularly those on invertebrates such as fruit flies, as largely irrelevant to investigations on human populations. In this paper I present life table data from large scale studies on the Mediterranean fruit fly, and show that they provide important insights into fundamental aspects of mortality relevant to human populations: the trajectory of mortality at older ages, sex mortality differentials, the concept of maximal life span, and demographic heterogeneity and selection. An overriding theme of the paper is the need for demographers to acquire a heightened awareness of new developments in biology including areas such as evolutionary ecology, experimental demography, and molecular medicine.     

The effects of maternal smoking on infant health

Maternal smoking has serious consequences for the developing fetus and infant, including a higher probability that the infant will be born prematurely and at low birth weight, will require admission to neonatal intensive care, and die during infancy. Data from Alabama birth certificates for births occurring between 1988 and 1991 were analyzed using log linear methods to calculate relative risks of adverse pregnancy outcomes and infant death. Smoking by mothers during pregnancy is associated with an elevated risk of infant death, low birth weight, and prematurity, controlling for mother's educational attainment, age, marital status, race, and trimester prenatal care was initiated. Smoking was also associated with a higher rate of admission to neonatal intensive care and to deaths from SIDS and respiratory causes. Reducing maternal smoking can contribute to a reduction of premature and low weight births and infant deaths. Because of the difficulty of stopping smoking, efforts need to be directed at preventing younger women from beginning to smoke.An earlier version of this paper was presented at the Southern Demographic Association annual meeting in New Orleans in October 1993.     

Eradication of the melon fly,Dacus cucurbitae, from Kume is., Okinawa with the sterile insect release method

Summary The sterile insect release method was applied to eradicate the melon fly,Dacus cucurbitae, from the 58.5 km² island of Kume, in the Okinawa Islands group. Weekly releases of 1 to 1.5 million flies irradiated as pupae with 6–7 kR from a cobalt-60 source did not decrease the wild melon fly population. Releases of 1.5–2 million pupae per week made from September, 1975 to January, 1976 decreased the percent egg-hatch of females caught on Kume Is., but did not decrease the percent infestation significantly. The number of pupae released was increased from February, 1976 to accelerate the eradication process. When the number of pupae released exceeded 3.5 million per week, a rapid increase in the ratio of marked (sterile) to unmarked (wild) flies, a remarkable decrease in percent egg-hatch, and a decrease in percent infestation of fruits were observed. There has been no sign of melon fly infestation in wild cucurbit fruits from October, 1976 to the present time (April, 1977), despite the fact that more than 70,000 fruits were carefully examined. The eradication of the melon fly from Kume Is. was thus achieved by April, 1977, after the release of 264 million sterile fly pupae.     

Weight loss and related behavior changes among lesbians

Overweight and obesity are known risk factors for several modifiable, if not preventable diseases. Growing evidence suggests that lesbians may have higher rates of obesity than other women. This study was designed to describe weight loss and behavior changes related to food choices and exercise habits among lesbians who participated in a predominantly lesbian, mainstream, commercial weight loss program. Behavioral changes were recorded in exercise, quality of food choices, and number of times dining out. Although there were several limitations based on sample size and heterogeneity, the impact of a lesbian-supportive environment for behavior change was upheld.     

A comparative study of the searching efficiencies of a parasite and a hyperparasite

Summary The searching efficiencies of a primary parasite (Diaeretiella rapae (McIntosh)) and a hyperparasite (Alloxysta brassicae (Ash.)) were investigated and compared. In both species, at all parasite densities, there was a curvilinear relationship (P<0.001) between the number of hosts parasitised and the host density. A linear regression (loga=logQ−m logP) was fitted for log area of discovery against log parasite density (P<0.001). The area of discovery for its immediate (i.e. primary) host (viz.Diaeretiella for the hyperparasite and aphid forDiaeretiella) is lower in the hyperparasite than in the primary parasite. InDiaeretialla both the searching efficiency and the mutual interference constant increased (but not significantly,P>0.05) in the presence of its males.     

The effects of food stamp receipt on weight gained by expectant mothers

With over 66% of Americans overweight, expectant mothers are unusual because they are encouraged to gain weight while pregnant. Food stamp receipt (FSR) may facilitate recommended weight gain by providing resources for food and nutrition. I examine the effects of FSR on the amount of weight gained by low-income expectant mothers using NLSY79 data. Results indicate FSR decreases the probability gaining insufficient weight but does not exacerbate the probability of gaining too much weight. Examining the effects of FSR on pregnancy weight gain is important because low birth weight is more likely when expectant mothers gain insufficient weight.