Female alternative reproductive behaviors: the effect of female group size on mate assessment and copying

Extensive theoretical and empirical research has focused on male alternative reproductive tactics. In comparison, female alternative tactics have attracted little attention, and further theoretical and empirical research are needed. Using a game theoretical model, we examine female choice alternatives (1) by considering assessment errors in a novel and more realistic manner than done previously, and (2) for the first time, by highlighting the formation of groups of females as an important consequence of copying behavior. We consider two alternatives: direct assessment of male quality by females and female copying of the choice of other females. Assessment and copying are predicted to coexist under a wide variety of circumstances and copying is favored when females make assessment errors, when high-quality males are either common or very rare, and when female fitness declines with the number of other females choosing the same male. We also find that the frequency of copying at equilibrium is predicted to decrease when the presence of other females mating with the same male has a positive effect on female fitness (e.g. through increased male parental effort, decreased predation risk or cooperation among females). Female alternative choice tactics also influence the potential for sexual selection. In our model, when the frequency of copying females is low, the potential for sexual selection can be higher than in the absence of female copying. However, contrary to previous theory, we find that as copying females become more common than assessing females, the potential for sexual selection will be low as more females copy the mate choice of other copiers without assessment.     

Outbreak of trichomoniasis in a woodpigeon (<Emphasis Type="Italic">Columba palumbus</Emphasis>) wintering roost

Large numbers of woodpigeons (Columba palumbus) winter each year in southwestern Spain and Portugal, where they feed on acorns. Although mortality in these wintering roosts is generally low, in winter and spring 2001 approximately 2,600 woodpigeons died from trichomoniasis. Diagnosis of the disease was based on postmortem examination, culture and identification of the parasite, Trichomonas gallinae, by PCR. Other viral, bacterial or fungal pathogens were ruled out as cause for the die-off. The gathering of the woodpigeons at game bird feeders set up for red-legged partridges may have contributed to the outbreak. Mortality ceased after treatment with dimetridazole via the game bird feeders. Supplementary feeding of game birds constitutes a risk factor for the appearance of disease outbreaks. Close monitoring of infectious diseases in these populations is important, but treatment of free-living birds should be avoided in favour of other measures, as it poses risks.     

Unpredictability induced by unfocused games in evolutionary game dynamics

Evolutionary game theory is a basis of replicator systems and has applications ranging from animal behavior and human language to ecosystems and other hierarchical network systems. Most studies in evolutionary game dynamics have focused on a single game, but, in many situations, we see that many games are played simultaneously. We construct a replicator equation with plural games by assuming that a reward of a player is a simple summation of the reward of each game. Even if the numbers of the strategies of the games are different, its dynamics can be described in one replicator equation. We here show that when players play several games at the same time, the fate of a single game cannot be determined without knowing the structures of the whole other games. The most absorbing fact is that even if a single game has a ESS (evolutionary stable strategy), the relative frequencies of strategies in the game does not always converge to the ESS point when other games are played simultaneously.     

公平规范与自然资源保护——在卧龙自然保护区的实验

以家庭承包管护模式实施的天然林保护在卧龙自然保护区取得了非常显著的积极效果.这一成功无法用理性的经济行为动机来解释,而公平性社会规范在这一过程中可能扮演着重要角色.为验证这一理论推断,在当地组织了一次性的最后通牒博弈实验,藉此了解公平性社会规范对当地人行为决策的实际影响情况.高度一致而显著偏离理性预期的实验结果表明当地人作为一个文化整体对于社会规范的普遍认同,其中96.9%的出价者在实验中给出了公平或超公平出价,表现出对公平的强烈偏好;而回应者较低的最低接受出价(17%±2.6%)又表明他们不愿对不公平出价者采取激烈的惩罚手段.当地人对家庭间合作的依赖和对公平声誉的看重可以解释这一对看似矛盾的实验结果,也证明基于声望的合作进化在小规模社会是现实可行的,而惩罚并非维持公平规范的必要因素.这一结果揭示了卧龙的天然林保护取得成功的关键因素,同时证明了利用公平性社会规范实现社区对自然资源保护工作的积极合作参与的可行性,从而支持了理论假说.这一实践经验对于经费不足的自然资源保护项目来说具有重要借鉴意义.     

Synergy and discounting of cooperation in social dilemmas

The emergence and maintenance of cooperation by natural selection is an enduring conundrum in evolutionary biology, which has been studied using a variety of game theoretical models inspired by different biological situations. The most widely studied games are the Prisoner's Dilemma, the Snowdrift game and by-product mutualism for pairwise interactions, as well as Public Goods games in larger groups of interacting individuals. Here, we present a general framework for cooperation in social dilemmas in which all the traditional scenarios can be recovered as special cases. In social dilemmas, cooperators provide a benefit to the group at some cost, while defectors exploit the group by reaping the benefits without bearing the costs of cooperation. Using the concepts of discounting and synergy for describing how benefits accumulate when more than one cooperator is present in a group of interacting individuals, we recover the four basic scenarios of evolutionary dynamics given by (i) dominating defection, (ii) coexistence of defectors and cooperators, (iii) dominating cooperation and (iv) bi-stability, in which cooperators and defectors cannot invade each other. Generically, for groups of three or more interacting individuals further, more complex, dynamics can occur. Our framework provides the first unifying approach to model cooperation in different kinds of social dilemmas.     

Putting competition strategies into ideal free distribution models: habitat selection as a tug of war

When resources are patchily distributed in an environment, behavioral ecologists frequently turn to ideal free distribution (IFD) models to predict the spatial distribution of organisms. In these models, predictions about distributions depend upon two key factors: the quality of habitat patches and the nature of competition between consumers. Surprisingly, however, no IFD models have explored the possibility that consumers modulate their competitive efforts in an evolutionarily stable manner. Instead, previous models assume that resource acquisition ability and competition are fixed within species or within phenotypes. We explored the consequences of adaptive modulation of competitive effort by incorporating tug-of-war theory into payoff equations from the two main classes of IFD models (continuous input (CI) and interference). In the models we develop, individuals can increase their share of the resources available in a patch, but do so at the costs of increased resource expenditures and increased negative interactions with conspecifics. We show how such models can provide new hypotheses to explain what are thought to be deviations from IFDs (e.g., the frequent observation of fewer animals than predicted in "good" patches of habitat). We also detail straightforward predictions made uniquely by the models we develop, and we outline experimental tests that will distinguish among alternatives.     

Involuntary defection and the evolutionary origins of empathy

An occasional involuntary defection (IVD)--being unable, rather than unwilling, to donate help to others--is an intrinsic attribute of reciprocal cooperation (2003. J. Theor. Biol. 225-285). In fact, it is easy to see that--barring special circumstances--individuals that can donate help whenever requested do not need help of the same kind from others. That is, it is by no means clear why such individuals should participate in symmetric reciprocity interactions. In this paper, I analyse the consequences of introducing IVD into direct reciprocity modeling and show that a simple form of empathy--not retaliating after being punished for IVD--is a prerequisite for evolutionarily stable cooperation. Furthermore: we will see that the stability of this, empathic retaliator, strategy increases with the number of opportunities for cooperative exchanges in the life of an average individual.     

Sex allocation and dispersal in a heterogeneous two-patch environment

We investigate the evolution of sex allocation and dispersal in a two-habitat environment using a game theoretic analysis. One habitat is of better quality than the other and increased habitat quality influences the competitive ability of offspring in a sex-specific manner. Unlike previous work, we allow incomplete mixing of the population during mating. We discuss three special cases involving the evolution of sex allocation under fixed levels of dispersal between habitats. In these special cases, stable sex-allocation behaviors can be both biased and unbiased. When sex-allocation behavior and dispersal rates co-evolve we identify two basic outcomes. First-when sex-specific differences in the consequences of spatial heterogeneity are large-we predict the evolution of biased sex-allocation behavior in both habitats, with dispersal by males in one direction and dispersal by females in the other direction. Second-when sex-specific differences are small-unbiased sex-allocation is predicted with no dispersal between habitats.