The effects of spatial and temporal environmental heterogeneities on persistence in a laboratory experimental community

Among many stabilizing factors for community dynamics, spatial and temporal heterogeneities have been widely considered in recent years as two of the most important properties. However, the difference between the two types of heterogeneities have not been studied, except for Clark and Yoshimura (1993). We evaluated experimentally the effect of temporal and spatial heterogeneities on the persistence of a biological community. The experimental communities consisted of one parasitic wasp species, one bean weevil species, and two kinds of bean. Temporal and spatial heterogeneities of experimental communities were generated by kinds and timing of bean supply. Of all the experimental communities, the most persistent community was a temporally and spatially homogeneous community with Red Kidney bean as primary resource. Compared to spatially heterogeneous communities, temporally heterogeneous communities were more persistent. These results were easily explained by considering the attack rate of parasitic wasps and the difference between arithmetic and geometric means. In order to discuss the relative importance of environmental heterogeneity and the mode of biological interaction on community persistence, we have to measure the degree of environmental heterogeneity as the rate of change of the strength of interspecific interactions.     

The outbreak mechanisms of the green rice leafhopper,Nephotettix cincticeps Uhler, in northern Japan

Intraspecific regulatory processes keep the population ofNephotettix cincticeps stable at a low density in southern Japan. In northern Japan, however, the yearly population density of the insect fluctuates violently, and large outbreaks occasionally take place. To clarify the difference in the population dynamics between the two regions, we analyzed light-trap and sweep-net sampling records from prefectural and national agricultural experimental stations. The survival rate of the overwintering population decreased with increases in the period of continuous snow cover (PCSC) in the north, and initial population densities in the years of long PCSC were too low for populations to reach equilibrium density by the end of the active breeding season. This made yearly population fluctuations in the north much larger than in the south. The equilibrium density in the north was higher than in the south. The higher equilibrium density presumably permits the higher population density and larger yearly population fluctuations in the north. A major factor responsible for the difference in equilibrium densities between the two regions is the difference in heading dates of the host plant (rice). Qualitative differences among rice plant varieties, and among biotypes ofN. cincticeps, may also be important.     

Personal probabilities of probabilities

By definition, the subjective probability distribution of a random event is revealed by the (‘rational’) subject's choice between bets — a view expressed by F. Ramsey, B. De Finetti, L. J. Savage and traceable to E. Borel and, it can be argued, to T. Bayes. Since hypotheses are not observable events, no bet can be made, and paid off, on a hypothesis. The subjective probability distribution of hypotheses (or of a parameter, as in the current ‘Bayesian’ statistical literature) is therefore a figure of speech, an ‘as if’, justifiable in the limit. Given a long sequence of previous observations, the subjective posterior probabilities of events still to be observed are derived by using a mathematical expression that would approximate the subjective probability distribution of hypotheses, if these could be bet on. This position was taken by most, but not all, respondents to a ‘Round Robin’ initiated by J. Marschak after M. H. De-Groot's talk on Stopping Rules presented at the UCLA Interdisciplinary Colloquium on Mathematics in Behavioral Sciences. Other participants: K. Borch, H. Chernoif, R. Dorfman, W. Edwards, T. S. Ferguson, G. Graves, K. Miyasawa, P. Randolph, L. J. Savage, R. Schlaifer, R. L. Winkler. Attention is also drawn to K. Borch's article in this issue.     

Abstracting and Indexing Adapts to the Internet Era

Abstract

With the role of libraries evolving from warehousing data sources to controlling the dissemination of information sources, A&I (abstracting and indexing) information services must also evolve and play an equally important and challenging role. With over forty years of A&I publishing experience, CSA (formerly Cambridge Scientific Abstracts) has adapted A&I publishing methods to new technologies and Web-based publishing. The editorial basics of producing A&I journals and databases are unchanged; however, new production technologies, such as electronic feeds between primary and secondary publishers, electronic directory services, and machine-aided indexing, can provide efficiencies. Once just roadmaps pointing to information, A&I services are now conduits delivering information directly to the user. Serials Review 2003; 29:221–223.     

Computer simulation study on the cyclicities ofTribolium population dynamics

Summary Under a set of assumptions, a mathematical model was constructed to investigate the effect of cannibalistic behavior and medium renewal schedule onTribolium population dynamics, and the results of simulation analyses were presented to show how modelling can contribute to a better understanding of experimental study. The analyses of the present model, the main concern of which is the cyclicity inTribolium population. showed that there are two distinct factors which create cyclicity, the cannibalistic behavior inTribolium itself, and the medium renewal schedule. Cannibalismper se does not necessarily cause cyclicity, but the combinations of cannibalistic behavior among various life stages and their relative intensities among them can cause cyclicity and can also determine the period of cycle. External factors also can generate cyclicity, but their interaction with cannibalistic behavior has a more significant effect in modifying the period of cycle. Some discrepancies between the model and experimental results were discussed.     

Differences in facilities' acceptance of patients under long-term care insurance in Japan

OBJECTIVES: In April 2000, Japan launched a public, long-term care insurance (LTCI) plan for elderly people who need support. This study describes how medical support for the elderly is delivered at LTCI care facilities in Japan now and gaps between system goals and current activity. Recommendations are made for enhancing the implementation of LTCI. METHODS: We mailed questionnaires to all health service facilities for the elderly (HSF) and special nursing homes for the elderly (SNH) located in the Kyushu area of Japan, asking whether they would accept patients with nine specific conditions. RESULTS: We found that HSFs, which are required to employ a full-time doctor and are reimbursed at a higher rate, accept significantly fewer patients with four conditions that need medical support than are accepted by SNHs, which are not required to employ a full-time doctor. DISCUSSION: In this study, we find discrepancies between system goals and current activities at LTCI care facilities. For the Japanese LTCI system to work well in the limitation of medical resources, we must understand how it really works and to reform the system continuously.     

Empirical Bayes Age–Period–Cohort Analysis of Retrospective Incidence Data

We analyse the (age, time)-specific incidence of diabetes based on retrospective data obtained from a prevalent cohort only including survivors to a particular date. From underlying point processes with intensities corresponding to the (age, time)-specific incidence rates the observed point pattern is assumed to be generated by an independent thinning process with parameters (assumed known) depending on population density and survival probability to the sampling date. A Bayesian procedure is carried out for the optimal adjustment and comparison of isotropic and anisotropic smoothing priors for the intensity functions, as well as for the decomposition of the intensity on the (time, age) Lexis diagram into the three factors of age, period and cohort.     

Pay-as-you-go social security and endogenous fertility in a neoclassical growth model

This paper theoretically studies how unfunded pay-as-you-go social security affects economic growth, the fertility rate, and welfare in a neoclassical growth model. In addition, this paper considers a more general form of child-rearing cost, which is a mixture of time and money. The first observation is that whether the fertility rate increases or not by the expansion of the pay-as-you-go social security depends on (1) the size of the monetary child-rearing cost relative to the time spent on child-rearing and (2) the current fertility and interest rate in laissez faire. The second observation is that income per worker can increase by an expansion in pay-as-you-go social security when the output elasticity of capital is sufficiently small and the payroll tax rate is high. The last finding is that welfare can be improved even though capital is underaccumulated in an economy.     

The dynamic transformation of political systems through social contract: a game theoretic approach

 We consider how the political system of the state evolves in the process of economic development. We present a dynamic public goods economy with non-overlapping generations, which confronts the free-rider problem without the state. In each generation, individuals enter under the unanimous rule a social contract of the political system, either monarchy or democracy, and then attempt to establish the state under the contracted political system. If the state is established, it provides public goods by enforcing tax on its members. Our game theoretic analysis shows: (i) the state can be established if and only if social productivity in terms of the capital stock of public goods is lower than a critical level; (ii) individuals choose democracy if social productivity is sufficiently high, while monarchy may be chosen if it is not; (iii) social productivity stochastically converges to the critical level over generations; and (iv) a simulation result shows several transformation patterns of political systems. Received: 21 June 1994/Accepted: 7 November 1995