Comparative studies on the seasonal occurrence, nymphal development and food menu in two giant water bugs,Diplonychus japonicus vuillefroy andDiplonychus major esaki (Hemiptera: Belostomatidae)

Summary We compared the seasonal changes in population density and nymphal development at different water temperatures and under different food conditions between two giant water bugs,Diplonychus japonicus andD. major, in Okayama, Japan. D. japonicus produced 1–2 generations a year, whileD. major was strictly inivoltine. The developmental velocity was higher inD. japonicus than inD. major. The thermal constant ofD. japonicus was less than that ofD. major. These results suggest thatD. japonicus is adapted, to higher water temperature thanD. major. In the field,D. japonicus preyed predominately on Lymnaeidae and Physidae snails, whileD. major preyed on aquatic insects such as dragonfly nymphs.     

A simple evolutionary model of dormancy and dispersal in heterogeneous patches with special reference to phytophagous lady beetles: I. Stable environments

Summary A simple evolutionary model of dormancy and dispersal is presented with special reference to phytophagous lady beetles. In order to investigate spatially heterogeneous environments, we assume the simplest patch structure, that is, there are only two patches, main and sub. Environments are also assumed to be temporally constant. The main patch is superior to the sub patch, but density effect at the main patch is higher than at the sub patch. Optimal dormancy and dispersal are obtained at the same time by the method of evolutionarily stable strategy (ESS). In the univoltine life cycle, dormancy strategy vanishes because dormant individuals do not reproduce at all but suffer from a certain mortality rate during winter hibernation. In the bivoltine life cycle, the dormancy and dispersal rates constitute a trade-off: the rates change together with a negative correlation when the mortality rate during dispersal or during winter hibernation changes. When suitability of the main patch gradually deteriorates, the optimal strategy changes as follows: neither dormancy nor dispersal is adopted at the most suitable condition, the dispersal rate is increased without dormancy in the intermediate condition, and then the dormancy rate is increased with a constant dispersal rate. We discuss the field observation data of lady beetles in the light of results of our model.     

Persistence of a fig wasp population and evolution of dioecy in figs: a simulation study

The relationship between fig trees and their pollinator wasps is a well-known example of species-specific obligate mutualism. In this article we present a stochastic model of this mutualistic system, referring to data on a dioecious fig (Ficus schwarzii) in Borneo, and examine the conditions for the persistence of a wasp population for a given period. (1) When the average duration of the flowering interval of fig trees is short, even a small fig population can sustain a wasp population successfully. A population whose average period of flowering cycle is half that of another population can sustain a wasp population with a number of trees less than half of the other population. (2) The wasp survival rate (WSR) is higher when (a) the variation of the interval periods of fig flowering is smaller, (b) the fig population size is larger, and (c) figs can prolong their receptivity to wait for a wasp if no wasps are available. (3) WSR is predictable from the average proportion of the fig's receptive phases, in which wasps are available, to their total receptive phases. (4) The persistence period of a wasp population increases exponentially with the number of fig trees. Based on these results we propose a new hypothesis, as a possible scenario, on the evolution of dioecy from monoecy in Ficus. Received: November 13, 1998 / Accepted: July 14, 1999     

图木舒克佛教故事图考

疏勒国和于阗、龟兹一样,当年为西域佛教大国,但是目前学界对疏勒佛教考古的研究却比较薄弱.20世纪初,法国学者伯希和在新疆图木舒克脱库孜萨来佛寺遗址发现几幅佛教故事图,90年代,该寺院遗址又出土了一件佛教故事图,这为研究佛教故事图在丝绸之路的流行提供了重要材料。本文将讨论这些佛教故事图的艺术风格和宗教内涵,探讨疏勒佛教性质.     

COLLATERAL CONSTRAINTS AND THE CURRENT ACCOUNT: THEORY AND EVIDENCE

We investigate the impact of domestic financial frictions on the current account dynamics in Asian countries before and after the Asian financial crisis in 1997–1998 by introducing collateral constraints into the intertemporal current account approach. We examine six Asian countries. Before the crisis, collateral constraints significantly impact the current account in Korea, Malaysia, the Philippines, and Thailand, but after the crisis, they do not. Our study shows that the impact of domestic financial frictions on the current account changes before and after a financial crisis. (JEL F32, F41)     

Resolution of evolutionary conflict: a general theory and its applications

While many cases in which conflict over the evolution of social behavior exists even between closely related individuals (e.g., parent-offspring conflict) have been pointed out, little attention has been paid on the problem of where such conflict should lead. A general theory of conflict resolution, however, has recently been developed. The key idea of the theory is the incorporation of conflict costs in the inclusive fitness evaluation. The theory shows that if both sides engaged in the conflict can potentially control the other at a cost, the coevolutionary game of escalating the fight with increased conflict costs always leads either side to give in to the other, resolving the conflict. Here we examine the logical basis of the theory in terms of a simplest example, donor-recipient conflict over the evolution of altruism, and to show its different types of application we review two more specific examples: reproductive-worker conflict over true (sterile) worker evolution in termites and insider-outsider conflict over group size determination. The latter exemplifies the resolution of conflict over the value of a variable (group size in this case) rather than a behavior, suggesting extended applicability of the basic theory.     

You Thought That This Would Be Easy? Seeking an Understanding of Episodic Volunteering

VOLUNTAS: International Journal of Voluntary and Nonprofit Organizations - This article is intended as the leading article in a Special Issue of Voluntas devoted to episodic volunteering from a...     

Episodic Volunteering in Sport Events: A Seven-Country Analysis

VOLUNTAS: International Journal of Voluntary and Nonprofit Organizations - Given its ubiquitous nature, sport events are one of the most popular venues for episodic volunteering around the world....     

Stabilization of the population of a parasite on fruit by the population of a cleptoparasite

Summary When there exist two species such that one is a parasite on fruit and the other exploits the parasitized fruits, they must compete for a limited resource with each other. The relation betweenDacus cucurbitae andAtherigona orientalis is an example of such a situation. We raise a question whether the population of a parasite on fruit can be stabilized by the existence of the cleptoparasite of the parasite on fruit. The changes in their population densities are represented as a differential equation with time delayed parameters, which is deduced from the context of life histories of the two species. An index representing degree of overlapping of generations (g) is defined as an average oviposition period devided by the average preoviposition period, and the value is assumed to be the same in the two species. The stability of the system is classified by three parameters: the reproductive rate of the parasite on fruits (R), the survival probability of it through competition against the cleptoparasite (p), and the generation overlapping index (g). For small values ofg, e.g. less than some 0.5, the stability is determined mainly by a product ofRp: the values larger than 1 result in no equilibrium and infinite increase of both species, the values near 0 lead to large amplitude oscillations, and the intermediate values make stable equilibria or regular small oscillations. Asg takes the larger values, the stability region in the space (p, R) occupies the larger area. The model presented here is well adjusted to the fluctuating pattern of the population ofD. cucurbitae on Okinawa Is., and would also be applied to analysis of both hyperparasitisms and inquilin. This study was supported partly by Science Research Fund (No. 574092) from the Ministry of Education, Japan.     

On the Restricted Liu Estimator in the Gauss–Markov Model

In this paper, we compare two estimators, the RLE (restricted Liu estimator) and the RLSE (restricted least squares estimator) of parameters in linear models under Gauss–Markov models. Using generalized inverse of matrices, we found some equivalency conditions for the superiority of the RLE with respect to the MSE criterion.