Population-level analysis on reduction in equilibrium population size of the azuki bean beetle

Summary Responses of laboratory population of the azuki bean beetleCallosobruchus chinensis to temperature conditions of 30°C and 32°C are compared. Equilibrium population size was found to be lower at 32°C. A one-generation process examined by reproduction-curve experiments is divided into two consecutive life stages specified by different habitats, i.e., outside and inside beans. Modified logistic difference equations are used to describe these population-level responses at each life stages. Sensitivity analysis is used to determine parameters of importance, thus determining the main cause of the reduced equilibrium population size at 32°C. The reduction resulted from the decrease in maximum population size of emerged adults which have experienced inside-bean process. The application and limitation of this population-level analysis to different levels are discussed.     

What motivates single women to save? the case of Japan

Using Japanese panel data, we analyze precautionary savings due to staying single in the presence of income uncertainty. Our panel analysis finds that compared with young women who are likely to get married within 3 years, those who are not plan to have 44 percent more savings for precautionary purposes, and 108 percent more for retirement. These results suggest that in facing higher risk of income fluctuation due to choosing to marry late or remain unmarried, young women intend to have more wealth to mitigate the income risk inherent in single life.     

Evolutionary character changes and population responses in an insect host-parasitoid experimental system

In an insect host (the cowpea weevilCallosobruchus maculatus)- parasitoidHeterospilus prosopidis) experimental system, the population densities of the component species oscillated for the first 20 generations and then abruptly stabilized as the parasitoid density decreased. Examination of the host and parasitoid after the 40th generation in the long-term experiment showed that (1) host larvae exhibited contest-type competition (killing other larvae inhabiting the same bean), in contrast to the founder population being scramble-type competitors and (2) the parasitoid attack rate on the host did not change. There was also an evolutionary trade-off between body size and the rates of larval survival and development, suggesting a cost of contest competition on larval survivorship and development. I tested model predictions (Tuda and Iwasa 1998) that (1) host equilibrium population size should gradually decrease as the proportion of the contest type increases and that (2) random attacks of the parasitoid on the host should reduce the rate of increase in proportion of the contest type, and the effect should become manifest especially during the first 20 generations. Two of three host-only replicates showed significant decrease in population sizes. Although the density of emerging adults per bean did not differ between replicates of the host-only and host-parasitoid systems, comparison of the host body size between them on day 270 (at the 13th generation) showed that the host was more contest-type in the host-only system than in the host-parasitoid system, as the model predicted, and later on day 650 the effect of the parasitoid had disappeared.     

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.     

Abating Stereotypical Attitudes: Views on Career Paths of an Asian American Comedian

An Asian American comedian, William Mar, provides an insightful commentary about his career choice. He believes that the comedy stage is a useful position to comment on stereotypes inherent to the American culture. Comedians must challenge the audience to think about the joke not only as amusement, but to examine the other implications involved.     

Density dependence depends on scale; at larval resource patch and at whole population

Summary A previous study (Tuda and Shimada, 1993) has shown that the equilibrium population size of the azuki bean beetle was lower at 32°C than at 30°C and that this difference was due to a reduced maximum population size of emerged progeny through inside-bean process. In this paper, these results were analyzed further on the scale of the individual bean where interaction among larvae took place. Per-bean numbers of deposited eggs, hatched eggs, and emerged adults have been recorded at seven different parental densities under the two temperature conditions. Three individual-bean-scale process hypotheses that may explain the reduced maximum emergence density on the whole population scale are suggested: (1) a lower maximum emergence per bean at 32°C than at 30°C, if the bean scale and the wholepopulation scale share the same density-dependent pattern in adult emergence, (2) a limited range of hatched egg number per bean at 32°C, resulting from the adult oviposition process outside beans, and (3) different patterns of density-dependent emergence between the two different scales. This study showed that the inside-bean pattern of responses on the bean scale was a simple saturated curve at 30°C, but one with a discontinuous decline at higher hatched egg densities at 32°C. On the contrary, during outside-bean process, the peak number of hatched eggs decreased on this scale as observed on the wholepopulation scale. I discuss why the extracted factor of inside-bean process on the whole-population in the previous study could not be applied to the bean-scale pattern.     

Ethics in context: essential flexibility in an international photo-elicitation project with children and young people

ABSTRACT

Existing literatures have discussed both ethical issues in visual research with young people, and the problems associated with applying ‘universal’ ethical guidelines across varied cultural contexts. There has been little consideration, however, of specific issues raised in projects where visual research is being conducted with young people simultaneously in multiple national contexts. This paper contributes to knowledge in this area. We reflect on our experiences of planning and conducting the International CYCLES project involving photo elicitation with young people in Bangladesh, Brazil, India, Japan, New Zealand, South Africa and the UK. While some issues such as varying access to technology for taking and sharing photos and diverse cultural sensitivities around the use of photography were anticipated in advance, others were more unexpected. Balancing the need for methods to be appropriate, ethical and feasible within each setting with the desire for sufficient consistency across the project is challenging. We argue that an ‘ethics in context’ approach and an attitude of ‘methodological immaturity’ is critical in international visual research projects with young people.     

Son preference in Japan

We examine the sex preference in Japan, using Japanese microdata, and find that parents in the 1920–1939 cohort have a lexicographic son preference. Further, the lexicographic son preference disappears in subsequent cohorts and a mixed preference is observed in parents with two children. These results are supported when the parents’ socioeconomic background is considered. Cohort effects such as weakening son preference and emerging mixed preference are observed. Moreover, when husbands are the eldest sons, a lexicographic son preference is observed only in the 1920–1939 cohort, although it persists in the subsequent cohorts when husbands are farmers/self-employed workers.     

Evolutionary and population dynamics of host–parasitoid interactions

The role of evolutionary dynamics in understanding host–parasitoid interactions is interlinked with the population dynamics of these interactions. Here, we address the problems in coupling evolutionary and population dynamics of host–parasitoid interactions. We review previous theoretical and empirical studies and show that evolution can alter the ecological dynamics of a host–parasitoid interaction. Whether evolution stabilizes or destabilizes the interaction depends on the direction of evolutionary changes, which are affected by ecological, physiological, and genetic details of the insect biology. We examine the effect of life history correlations on population persistence and stability, embedding two types, one of which is competitively inferior but superior in encapsulation (for parasitoid, virulence), in a Nicholson–Bailey model with intraspecific resource competition for host. If a trade-off exists between intraspecific competitive ability and encapsulation (or virulence, as a countermeasure) in both the host and parasitoid, the trade-off or even positive correlation in the parasitoid is less influential to ecological stability than the trade-off in the host. We comment on the bearing this work has on the broader issues of understanding host–parasitoid interactions, including long-term biological control. Received: November 10, 1998 / Accepted: January 18, 1999     

The equivalence of the cost share equilibria and the core of a voting game in a public goods economy

We consider a social situation where individuals choose one or some alternative(s) from a set of feasible alternatives. When one alternative is socially chosen, each individual must share the cost for it according to an exogenously given sharing rule. Individuals are allowed to collude among themselves through money transfers. As the mechanism of choosing a social alternative, we consider the cost share equilibrium and a voting game. The cost share equilibrium is an allocation where each individual maximizes his/her utility independently and where unanimity is still maintained. We will show the equivalence between the set of all equilibrium allocations and the core of the voting game with compensation.I would like to thank Professors Mamoru Kaneko, Kotaro Suzumura, William Thomson, Mikio Nakayama, Hiroo Sasaki, Mr. Ken-ichi Shimomura and anonymous referees for their many useful suggestions and comments. I also acknowledge grammatical suggestions of Mr. Ronald M. Siani.