Hunting behavior of wild chimpanzees in the Taï National Park

Hunting is often considered one of the major behaviors that shaped early hominids' evolution, along with the shift toward a drier and more open habitat. We suggest that a precise comparison of the hunting behavior of a species closely related to man might help us understand which aspects of hunting could be affected by environmental conditions. The hunting behavior of wild chimpanzees is discussed, and new observations on a population living in the tropical rain forest of the Taï National Park, Ivory Coast, are presented. Some of the forest chimpanzees' hunting performances are similar to those of savanna-woodlands populations; others are different. Forest chimpanzees have a more specialized prey image, intentionally search for more adult prey, and hunt in larger groups and with a more elaborate cooperative level than savanna-woodlands chimpanzees. In addition, forest chimpanzees tend to share meat more actively and more frequently. These findings are related to some theories on aspects of hunting behavior in early hominids and discussed in order to understand some factors influencing the hunting behavior of wild chimpanzees. Finally, the hunting behavior of primates is compared with that of social carnivores.     

Population structure,spite, and the iterated Prisoner's Dilemma

Evolutionary stability (sensu Maynard Smith: Evolution and the Theory of Games, Cambridge: Cambridge University Press, 1982) of TIT FOR TAT (TFT) under the social ecology of the iterated Prisoner's Dilemma is a function of the number of pure TFT groups (dyads) in the population, relative to the social position of a focal invading defector. Defecting against TFT always raises the defector's relative intragroup fitness; when Axelrod's (Am. Polit. Sci. Rev. 75:306–318, 1981; The Evolution of Cooperation. New York: Basic Books, 1984) Evolutionary stable strategy (ESS) conditions are met, defection also lowers the absolute fitness of the defector. Here the retaliatory (punishing) character of TFT converts defection into spite, permitting pure TFT groups to sufficiently outproduce the defector for the latter's evolutionary suppression. Increasing the relative impact of spiteful defection on a population lowers the range of evolutionary stability for TFT. When individuals participate in multiple dyads, those participating in the greatest number of dyads are most likely to provide a vehicle for the successful invasion of defection. Within social networks, ESS conditions for TFT are thus individual specific. This logic is generalized to the context of an interated n-person Prisoner's Dilemma, providing a cooperative solution conceptually identical with TFT in the two-person game.     

Do chimpanzees cooperate in a learning task?

The aim of this study was to assess the ability of chimpanzees (Pan troglodytes) to cooperate in an instrumental task. A specially constructed fruit distributor was presented to a group of six captive chimpanzees. A cooperative response required two chimpanzees: both had to pull a handle simultaneously to make a fruit fall into the cage. The dominant male of the group and an infant produced most of the operant responses, and the male got nearly all the fruits. Other conspecifics avoided the dominant male at the apparatus. Social influences appear to limit the possibility of co-operation between individuals because a certain level of interindividual tolerance is required. The results revealed a significant increase in the number of pulls each time both chimpanzees were together at the apparatus. Operant chimpanzees learn to coordinate their actions in time and space.     

Genetic Evaluation and Utilization (GEU) program

Summary The Genetic Evaluation and Utilization (GEU) program of the International Rice Research Institute (IRRI) is an interdisciplinary program for the improvement of rice crops. Scientists trained in diverse disciplines such as plant breeding, plant pathology, entomology, agronomy, cereal chemistry, plant physiology, and soil chemistry work together and contribute their specialized skills to this joint endeavor. The program has five interrelated components: (1) germ plasm collection and conservation, (2) research in disciplinary areas, (3) development of improved germ plasm, (4) distribution, evaluation and exchange of germ plasm internationally, (5) training of young scientists.Over forty thousand rice varieties from different countries are being maintained in the IRRI germ plasm bank. These varieties have been screened for grain quality, resistance to various diseases and insects, and tolerance to various environmental stresses such as drought, high and low temperatures and problem soils. Donor parents for resistances to each of the problem areas have been identified. These parents were utilized for developing improved germ plasm. Varieties with resistance to as many as five diseases and five insect species have been developed. These multiple resistant varieties are grown on millions of hectares of rice land. Seeds of improved breeding materials are exchanged internationally and 194 scientists from different countries have been trained in rice improvement work.     

Social contact and hormonal changes predict post-conflict cooperation between friends

Long-term cooperation between individuals necessitates repairing damage arising from inevitable competing interests. How two members of a valuable relationship switch from competing to cooperating constitutes an important problem for any social species. Observations of non-human animals suggest that affiliative contact immediately following a contest facilitates continued cooperation. Behavioral studies further indicate that winners and losers frequently differ in hormonal changes following a competition. We tested the hypothesis that immediate contact with increases in cortisol (and testosterone for men) for winners following competition would facilitate subsequent cooperation between adult same-sex friends. Results show that contact (versus no contact) immediately following competition enhanced subsequent cooperation between female friends. During contact, increases in winner's cortisol for both sexes, and in testosterone for men, predicted future cooperation. Our results suggest two mechanisms that maintain social bonds following competition between established allies.     

A tale of two defectors: the importance of standing for evolution of indirect reciprocity

Indirect reciprocity occurs when the cooperative behavior between two individuals is contingent on their previous behavior toward others. Previous theoretical analysis indicates that indirect reciprocity can evolve if individuals use an image-scoring strategy. In this paper, we show that, when errors are added, indirect reciprocity cannot be based on an image-scoring strategy. However, if individuals use a standing strategy, then cooperation through indirect reciprocity is evolutionarily stable. These two strategies differ with respect to the information to which they attend. While image-scoring strategies only need attend to the actions of others, standing strategies also require information about intent. We speculate that this difference may shed light on the evolvability of indirect reciprocity. Additionally, we show that systems of indirect reciprocity are highly sensitive to the availability of information. Finally, we present a model which shows that if indirect reciprocity were to evolve, selection should also favor trusting behavior in relations between strangers.     

Spatial Patterns of Prisoner’s Dilemma Game in Metapopulations

Because to defect is the evolutionary stable strategy in the prisoner’s dilemma game (PDG), understanding the mechanism generating and maintaining cooperation in PDG, i.e. the paradox of cooperation, has intrinsic significance for understanding social altruism behaviors. Spatial structure serves as the key to this dilemma. Here, we build the model of spatial PDG under a metapopulation framework: the sub-populations of cooperators and defectors obey the rules in spatial PDG as well as the colonization–extinction process of metapopulations. Using the mean-field approximation and the pair approximation, we obtain the differential equations for the dynamics of occupancy and spatial correlation. Cellular automaton is also built to simulate the spatiotemporal dynamics of the spatial PDG in metapopulations. Join-count statistics are used to measure the spatial correlation as well as the spatial association of the metapopulation. Simulation results show that the distribution is self-organized and that it converges to a static boundary due to the boycotting of cooperators to defectors. Metapopulations can survive even when the colonization rate is lower than the extinction rate due to the compensation of cooperation rewards for extinction debt. With a change of parameters in the model, a metapopulation can consist of pure cooperators, pure defectors, or cooperator–defector coexistence. The necessary condition of cooperation evolution is the local colonization of a metapopulation. The spatial correlation between the cooperators tends to be weaker with the increase in the temptation to defect and the habitat connectivity; yet the spatial correlation between defectors becomes stronger. The relationship between spatial structure and the colonization rate is complicated, especially for cooperators. The metapopulation may undergo a temporary period of prosperity just before the extinction, even while the colonization rate is declining. An erratum to this article can be found at     

Evolutionary graph theory: breaking the symmetry between interaction and replacement

We study evolutionary dynamics in a population whose structure is given by two graphs: the interaction graph determines who plays with whom in an evolutionary game; the replacement graph specifies the geometry of evolutionary competition and updating. First, we calculate the fixation probabilities of frequency dependent selection between two strategies or phenotypes. We consider three different update mechanisms: birth-death, death-birth and imitation. Then, as a particular example, we explore the evolution of cooperation. Suppose the interaction graph is a regular graph of degree h, the replacement graph is a regular graph of degree g and the overlap between the two graphs is a regular graph of degree l. We show that cooperation is favored by natural selection if b/c>hg/l. Here, b and c denote the benefit and cost of the altruistic act. This result holds for death-birth updating, weak-selection and large population size. Note that the optimum population structure for cooperators is given by maximum overlap between the interaction and the replacement graph (g=h=l), which means that the two graphs are identical. We also prove that a modified replicator equation can describe how the expected values of the frequencies of an arbitrary number of strategies change on replacement and interaction graphs: the two graphs induce a transformation of the payoff matrix.     

Examining the relatedness of behaviors through experimentation: switching on and off chewing and feeding behaviors in a parasitic wasp

Melittobia digitata (Hymenoptera: Eulophidae) are parasitoids known for their cooperative escape behavior. The initial sequences of this escape chewing behavior have been compared to the initial sequences of their feeding behavior. We sought to experimentally test whether these sequences were interchangeable. We were successful in turning off chewing and turning on feeding in a chewing situation, and turning on chewing and turning off feeding in a feeding context. We discuss the implications of this finding for the origin and evolution of these behaviors, and how experimental tests of key cues can be helpful for understanding the evolution of behavioral patterns.     

Eco(nomics/logy)

This note discusses the analytic tools available for studying the interrelations between the economy and the ecological system. It points out the importance of the concept of cooperative games as an addition to the emphasis on non-cooperative games in both economics and ecology. The relation between both concepts of the games and the market system is discussed.