Abstract: Bekoff [J. Consci. Stud. 8 (2001) 81] argued that mammalian social play is a useful behavioral phenotype on which to concentrate in order to learn more about the evolution of fairness. Here, we build a game theoretical model designed to formalize some of the ideas laid out by Bekoff, and to examine whether `fair' strategies can in fact be evolutionarily stable. The models we present examine fairness at two different developmental stages during an individual's ontogeny, and hence we create four strategies--fair at time 1/fair at time 2, not fair at time 1/not fair at time 2, fair at time 1/not fair at time 2, not fair at time 1/fair at time 2. Our results suggest that when considering species where fairness can be expressed during two different developmental stages, acting fairly should be more common than never acting fairly. In addition, when no one strategy was evolutionarily stable, we found that all four strategies we model can coexist at evolutionary equilibrium. Even in the absence of an overwhelming database from which to test our model, the general predictions we make have significant implications for the evolution of fairness.

Abstract: One specific prediction emerging from trait-group models of natural selection is that when individuals possess traits that benefit other group members, natural selection will favor “cheating” (i.e. not possessing the group-beneficial trait) within groups. Cheating is selected within groups because it allows individuals to avoid bearing the relative costs typically associated with group-beneficial traits, but to still reap the benefits associated with the acts of other group members. Selection between groups favors traits that benefit other group members. The relative strength of within- and between-group selection then determines the equilibrium frequency of those who produce group-beneficial traits and those that do not. Here we demonstrate that individual-level selection, that is selection within groups can also produce an intermediate frequency of such group-beneficial traits by frequency-dependent selection. The models we develop are general in nature, but were inspired by the evolution of antibiotic resistance in bacteria. The theory developed here is distinct from prior work that relies on reciprocity or kinship per'se to achieve cooperation and altruism among group members.

Abstract: We present the results of a series of computer simulations that examined the impact of winner, loser, and bystander effects on hierarchy formation in fused groups. These effects and their implications for hierarchy structure and aggressive interactions were first examined in small four-member groups. Subsequent to this, the two small groups were fused into a single larger group. Further interactions took place in this fused group, generating a new hierarchy. Our models demonstrate clearly that winner, loser, and bystander effects strongly influence both the structure and types of interactions that emerge from the fusion of smaller groups. Four conditions produced results in which the same general patterns were uncovered in pre- and postfusion groups: (1) winner effects alone, (2) bystander loser effects alone, (3) winner and bystander winner effects operating simultaneously, and (4) all four effects in play simultaneously. Outside this parameter space, hierarchy structure and the nature of aggressive interactions differed in pre- and postfusion groups. When only loser effects were in play, one of the two clear alphas from the prefused groups dropped in rank in the eight-member fused group. When bystander winner effects were in play, it was difficult to rank any of the eight individuals in the fused group, and players interacted almost exclusively with those that were not in their original four-member group. When loser and bystander loser effects operated simultaneously, two top-ranking individuals emerged in the fused groups, but the relative rank of the other players was difficult to assign.

Abstract: In the literature on dominance hierarchies, “winner” and “loser” effects usually are denned as an increased probability of winning at time T, bated on victories at time T-l, T-2, etc, and an increased probability of losing at time T, based on losing at T-1, T-2, etc., respectively. Despite some early theoretical work on winner and loser effects, these factors and how they affect the structure of dominance hierarchies have not been examined in detail. I developed a computer simulation to examine winner and loser effects when such effects are independent of one another (as well as when they interact) and when combatants assess each other's resource-holding power. When winner effects alone were important, a hierarchy in which all individuals held an unambiguous rank was found. When only loser effects were important, a dear alpha individual always emerged, but the rank of others in the group was often unclear because of the scarcity of aggressive interactions. Increasing winner effects for a given value of the loser effect increase the number of individuals with unambiguous positions in a hierarchy and the converse is true for increasing the value of the loser effect for a given winner effect Although winner and loser effects have been documented in a number of species, no study has documented both winner and loser effects (using some controlled, pairwise testing system) and the detailed nature of behavioral interactions when individuals are in groups. I hope the results of this model will spur such studies in the future.

Abstract: Guppies,Poecilia reticulata, living in stream pools in Trinidad, West Indies, approached a potential fish predator (a cichlid fish model) in a tentative, saltatory manner, mainly as singletons or in pairs. Such behavior is referred to as predator inspection behavior. Inspectors approached the trunk and tail of the predator model more frequently, more closely and in larger groups than they approached the predator's head, which is presumably the most dangerous area around the predator. However, guppies were not observed in significantly larger shoals in the stream when the predator model was present. In a stream enclosure, guppies inspected the predator model more frequently when it was stationary compared to when it was moving, and made closer inspections to the posterior regions of the predator than to its head. Therefore, the guppies apparently regarded the predator model as a potential threat and modified their behavior accordingly when inspecting it. Guppies exhibited a lower feeding rate in the presence of the predator, suggesting a trade-off between foraging gains and safety against predation. Our results further suggest that predator inspection behavior may account for some of this reduction in foraging. These findings are discussed in the context of the benefits and costs of predator inspection behavior.