"Less is More: An Observability Paradox in Repeated Gamess"

We present a repeated prisoners' dilemma game with imperfect public monitoring, which exhibits the following paradoxical feature: the equilibrium payoff set expands and asymptotically achieves full efficiency as the public signal becomes less sensitive to the hiden actions of the players.

"Efficiency in Repeated Games Revisited: The Role of Private Strategies"

Most theoretical or applied research on repeated games with imperfect monitoring has restricted attention to public strategies; strategies that only depend on history of publicly observable signals, and perfect public equilibrium (PPE); sequential equilibrium in public strategies. The present paper sheds light on the role of private strategies; strategies that depend on players' own actions in the past as well as observed public signals. Our main finding is that players can sometimes make better use of information by using private strategies and efficiency in repeated games can often be drastically improved. We illustrate this for both games with a small signal space (Anti-folk theorem example) and games with a large signal space, for which the Folk Theorem holds. Our private strategy can be regarded as a machine which consists of two states. We provide two di erent characterizations of our two-state machine equilibrium for general two-person repeated games with imperfect public monitoring.

Heterogeneous Impacts of Grazing Animals and Vegetational Change in Japanese Native Pastures

Defoliation, defecation and trampling are the major modes whereby grazing animals give impacts on vegetation. Due to the uneven distribution, such grazing behavior can have profound effects on vegetation. For extensive grazing systems in native pastures, understandings of the plant-animal interaction are vital for adequate control of vegetation and animal conditions and sustainable use of natural resources. This paper reviews recent studies of the grazing impacts on vegetation in Japanese native pastures. Most of the studies were carried out in the Kawatabi Field Science Center (Kawatabi FSC), Tohoku University. 1.Native pastures in the Kawatabi FSC are composed of 61-155 plant species, of which cattle graze upon 26-76 species. Among these species, Miscanthus sinensis (Japanese plume-grass) was the most frequently grazed by cattle. The spatial distribution of available forage is a major factor affecting diet selection and consumption of cattle. Such selective grazing results in significant reduction of M. sinensis in native pastures. 2.Seed dispersal of plants by defecation of grazing animals can also result in significant vegetational change. Recent studies have shown that Carex spp. is the major plant whose seeds are dispersed by defecation of animals rotationally grazed in a native and a sown pasture. The mechanisms of the seed dispersal and its possible effects on vegetational succession are discussed. 3.Heavy trampling is known to degrade vegetative ground cover. Our research has shown that trampling by cattle promotes the invasion of a shrub, Weigela hortensis into Miscanthus-dominant pastures. Because the seeds of W. hortensis are light sensitive germinators, trampling by removing ground cover promotes its seed germination. These findings provide new perspectives on plantanimal interactions in Japanese native pastures and help estimate the impact of animals on plant succession. They also contribute to efforts to ensure sustainable grazing use of pastures

Less is More : An Observability Paradox in Repeated Games

We present a repeated prisoners\u27dilemma game with imperfect public monitoring, which exhibits the following paradoxical feature: the equilibrium payoff set expands and asymptotically achieves full efficiency as the public signal becomes less sensitive to the hiden actions of the players.本文フィルはリンク先を参照のこ

Efficiency in Repeated Games Revisited : The Role of Private Strategies

Most theoretical or applied research on repeated games with imperfect monitoring has restricted attention to public strategies; strategies that only depend on history of publicly observable signals, and perfect public equilibrium (PPE); sequential equilibrium in public strategies. The present paper sheds light on the role of private strategies; strategies that depend on players'own actions in the past as well as observed public signals. Our main finding is that players can sometimes make better use of information by using private strategies and efficiency in repeated games can often be drastically improved. We illustrate this for both games with a small signal space (Anti-folk theorem example) and games with a large signal space, for which the Folk Theorem holds. Our private strategy can be regarded as a machine which consists of two states. We provide two di erent characterizations of our two-state machine equilibrium for general two-person repeated games with imperfect public monitoring

Less is More : An Observability Paradox in Repeated Games

We present a repeated prisoners'dilemma game with imperfect public monitoring, which exhibits the following paradoxical feature: the equilibrium payoff set expands and asymptotically achieves full efficiency as the public signal becomes less sensitive to the hiden actions of the players