A preliminary study on quantitative relations among growth, reproduction and mortality in fishes

Summary As a quantitative approach to the life histories of fishes, the present paper attempted to predict a relation among reproduction, growth and mortality numerically with a technique of control theory, the discrete maximum principle. A method for predicting the relation was derived on the postulate that natural selection maximized the net reproductive rate subject to a few constraints. The derived method was applied to Atlantic cod and Atlantic herring populations in the Southern Gulf of St. Lawrence as numerical examples. The examples demonstrated that the theoretical reproductive effort and body weight were well consistent with the observed ones every age but the theoretical survival rates were slightly different from the observed ones. For the reasons mentioned below, however, it should be interpreted that the examples rather support the adopted postulate to a certain degree. First, in general, it is very difficult to obtain good estimates of the rates with traditional methods. Second, intense fishing pressure possibly changes the life history parameters to some extent in fish populations. Moreover, the examples also suggested that, to examine the postulate in further detail, similar analyses had to be made with the data of many fish populations on which intense fishing pressure had not been exerted.     

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.     

THE EMERGENCE OF TRENDSETTERS FOR FASHIONS AND FADS:

Analyses of fads and fashions often note the importance of trendsetters whose early adoption of novelties provides an example for others to follow. However, trendsetting is usually taken for granted; there is no effort to explain why some groups assume fashion leadership. This article seeks to account for the rise of kogaru (stylish high-school girls) as trendsetters in 1990s Japan. We argue that trendsetting requires resources—particularly leisure time to devote to fashion, disposable income, and communication networks. Kogaru became trendsetters because they gained these resources at a time when the female college students who preceded them had less time for trendsetting, and when economic recession made inexpensive items of the sort kogaru could afford more desirable fashion objects. At the same time, new electronic technologies sped the flow of information among kogaru, while media coverage of this new social type gave kogaru visibility in the larger society.     

Historical Experience and the Haitian Revolution in the History Classroom

The article examines a mainstream curricular unit on the Haitian Revolution, centered on a culminating role-play activity. Cultural studies, subaltern studies, and hermeneutics are applied as theoretical frameworks to read the curriculum unit and its activities. These theoretical lenses sharpen an understanding of what it means to experience history in the classroom. These lenses are used to consider the political relations of power within the historical moment being studied and the political notions of power within the production of historical knowledge itself. The author conducts an analysis of the epistemological and hermeneutic problem spaces within this curriculum, with particular attention to how this curriculum unit might be translated into an urban school setting that accounts for marginalized student positions.     

How small can the difference among competitors be for coexistence to occur

Closely related competitors comprising ofEscherichia coli strains having the same metabolic system and differing only with a few bases on the glutamine synthetase gene in the plasmid pKGN were previously shown to coexist in a chemostat. The differences among these closely related competitors can be considered large enough to allow coexistence as the level of enzyme activity is different. To bring the difference among competitors to the slightest possible, the mutation was introduced on the noncoding region of the plasmid pKGN harbored in the wild-type strain (strain W). The new strain, strain W’, carries the plasmid pKGN’ with a 4-base insertion at theHind III site in the polycloning site of pKGN. As the noncoding region is a nucleotide segment that is not translated into amino acids, the relatedness between strains W and W’ is the closest possible from the genetic point of view. Interestingly, though both strains are almost identical, they can coexist stably in a chemostat irrespective of the initial population size. These experimental results suggest that in the natural ecosystem, no matter how akin competitors are, coexistence is not impossible.     

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.     

Corrigendum to “Games With Imperfectly Observable Actions in Continuous Time”

Sannikov (2007) investigated properties of perfect public equilibria in continuous‐time repeated games. This note points out that the proof of Lemma 6, required for the proof of the main theorem (Theorem 2), contains an error in computing a Hessian matrix. A correct proof of Lemma 6 is provided using an additional innocuous assumption and a generalized version of Lemma 5.     

A phase expansion for non-Markovian availability models with time-based aperiodic rejuvenation and checkpointing

Abstract

This paper presents a stochastic framework, consisting of stochastic reward net (SRN) for capturing the transient behaviors of the system and its related non-Markovian state transition diagram, to model an operational software system that undergoes aperiodic time-based rejuvenation and checkpointing schemes, and further to investigate whether there exists the optimal rejuvenation schedule that maximizes the system steady-state availability. A phase expansion approach is adopted to solve the non-Markovian availability models, which are actually neither the semi-Markov processes nor the Markov regenerative processes. Our numerical results show an appropriate rejuvenation trigger timing range, resulting in the positive improvement effect on the system availability of a database system, and that there exists the optimal rejuvenation trigger timing maximizing the system availability.     

Variational Bayes for Phase-Type Distribution

This article develops an algorithm for estimating parameters of general phase-type (PH) distribution based on Bayes estimation. The idea of Bayes estimation is to regard parameters as random variables, and the posterior distribution of parameters which is updated by the likelihood function provides estimators of parameters. One of the advantages of Bayes estimation is to evaluate uncertainty of estimators. In this article, we propose a fast algorithm for computing posterior distributions approximately, based on variational approximation. We formulate the optimal variational posterior distributions for PH distributions and develop the efficient computation algorithm for the optimal variational posterior distributions of discrete and continuous PH distributions.