The effects of information in a resource management problem: A social trap analog

A resource management simulation was devised in which players could harvest points for individual short-term gain, causing the premature destruction of the resource pool, or they could curb their own individual harvesting to preserve the pool for a longer overall supply. Although the first strategy was explained to be self-defeating, most groups opted for it, as they did even when an optimal harvesting strategy was provided that would avoid pool destruction. Groups whose members were allowed to communicate generally made better resource managers and achieved larger individual harvests.     

Spatial dynamics,social norms,and the opportunity of the commons

The most important message of Levin (Ecol Res 21:328–333, 2006) is that “Ecologists and economists have much incentive for interaction.” Recent studies that account for evolutionary processes and local interactions support this view by obtaining results that run counter to conventional wisdom within resource economics. A second major message of the article is that to meet environmental challenges, humanity must develop social norms that enhance cooperative responses. Successful examples of resource management systems back up norms with economic incentives: rewards for good behavior and punishments for bad. Economic incentives are especially important if rapid and large changes in human behavior are desired.     

Diminishing returns in social evolution: the not-so-tragic commons

A challenge for evolutionary theory is to understand how cooperation can occur in the presence of competition and cheating, a problem known as the tragedy of commons. Here I examine how varying the fitness returns from reproductive competition or cooperation affects the negative impact of competition on a social group. Varying linear returns does not affect the impact of competition. However, diminishing returns, where additional investments in either competition or cooperation give smaller and smaller rewards, reduce the effects of competition on the group. I show that diminishing returns are common in many systems, including social vertebrates, microbes, social insects and mutualisms among species. This suggests that the tragedy of the commons is not so tragic and that the disruptive effects of competition upon social life will often be minor.     

An experimental removal of a territorial pomacentrid: effects on the occurrence and behavior of competitors

Synopsis Stegastes fasciolatus is the most common territorial damselfish in the shallow waters of Hawaii. Territorial defense was observed against other herbivorous fishes, especially acanthorids, scarids and one omnivorous chaetodontid. One acanthurid,Acanthurus nigrofuscus was found to differ in abundance and social behavior in areas whereS. fasciolatus was present, compared to areas where it was absent. The chaetodontid,Chaetodon quadrimaculatus was sheltered during the day in areas where the pomacentrid was abundant, apparently feeding at night. In other areas it fed during the day and at night, depending on the phase of the moon.S. fasciolatus were then experimentally removed from one study site, to test whether the differences in abundance and behavior of the other species were due to the presence of the damselfish. There was a significant increase in numbers of the surgeonfishAcanthurus nigrofuscus in the removal area, as well as changes in social behavior from schooling to defense of small territories. The butterflyfish,C. quadrimaculatus, was observed to forage during the day in the removal area. There were no significant changes in the control sites. The presence of the interspecifically territorial damselfish,S. fasciolatus, thus appears to be an important determinant of the behavior of these potential food competitors.     

The evolutionary palaeoecology of species and the tragedy of the commons

The fossil record presents palaeoecological patterns of rise and fall on multiple scales of time and biological organization. Here, we argue that the rise and fall of species can result from a tragedy of the commons, wherein the pursuit of self-interests by individual agents in a larger interactive system is detrimental to the overall performance or condition of the system. Species evolving within particular communities may conform to this situation, affecting the ecological robustness of their communities. Results from a trophic network model of Permian-Triassic terrestrial communities suggest that community performance on geological timescales may in turn constrain the evolutionary opportunities and histories of the species within them.     

The effects of male body size on territorial and mating success in the landmark-defending fly Hermetia comstocki (Stratiomyidae)

Abstract.

• 1 Males of Hermetia comstocki Williston compete for territorial control of certain agaves and yuccas. Winners copulate with females that visit these plants solely to acquire a mate.
• 2 Males vary in body weight by more than an order of magnitude and larger flies almost always defeat smaller ones in aerial contests for control of landmark territories.
• 3 The mean body size (as measured by wing-length) was significantly greater for males retaining residency at a site for at least one hour compared to males unable to do so. Likewise, males able to return to a perch site in the study area on more than one day were larger on average than males unable to do so.
• 4 Male preferences for landmark territories remained similar across years. Large males dominated the perch landmarks most likely to be occupied by males and most likely to be visited by females.
• 5 Despite the fighting and territorial advantages enjoyed by large males, the mean size of males found mating with females was not significantly larger than that of the general population.
• 6 The apparent failure of large males to secure a statistically significant mating advantage may be a statistical consequence of the small sample size of males observed mating. On the other hand, any mating advantage of large males may be reduced because (a) receptive females visit many different landmarks, (b) females mate with the first male they encounter at a landmark, regardless of his size, (c) there are usually many vacant landmarks available for smaller males, and (d) even popular territories are often open to small males, thanks to the low site-tenacity of territory owners.

     

Cooperation as a volunteer’s dilemma and the strategy of conflict in public goods games

Conflict and cooperation for the exploitation of public goods are usually modelled as an N‐person prisoner’s dilemma. Many social dilemmas, however, would be described more properly as a volunteer’s dilemma, in which a certain number of individuals are necessary to produce a public good. If volunteering is costly, but so is failure to produce the public good, cheaters can invade and form a stable mixed equilibrium with cooperators. The dilemma is that the benefit for the group decreases with group size because the larger the group is, the less likely it is that someone volunteers. This problem persists even in the presence of a high degree of relatedness between group members. This model provides precise, testable predictions for the stability of cooperation. It also suggests a counterintuitive but practical solution for this kind of social dilemmas: increasing the damage resulting from the failure to produce the public good increases the probability that the public good is actually produced. Adopting a strategy that entails a deliberate risk (brinkmanship), therefore, can lead to a benefit for the society without being detrimental for the individual.     

Resolving the tragedy of the commons: the feedback between intraspecific conflict and population density

Competition and conflict among individuals can favour exploitative strategies that undermine the common good. Theory suggests that this can lead to a tragedy of the commons and ultimately population extinction, a phenomenon known as evolutionary suicide. Here, I present a model of the evolutionary tragedy of the commons that explicitly considers the population dynamics where individuals invest in individually costly competitive traits. In the simplest form, this supports the notion that selection for high levels of conflict can cause evolutionary suicide. However, as competition comes with survival and fecundity costs, a feedback between the investment in competition and population density can act to reduce the level of conflict and prevent the population from going extinct. This suggests that the interaction between population ecology and the evolution of competition and conflict among individuals may be an important mechanism in resolving the level of competition and conflict among individuals.     

The volunteer's dilemma and the optimal size of a social group

If one or few individuals are enough to perform an action that produces a collective good and if this action has a cost, living in group can be beneficial because the cost can be shared with other individuals. Without coordination, however, the production of a collective good by the contribution of one or few individuals is inefficient and can be modelled as a volunteer's dilemma. In the volunteer's dilemma the individuals that pay the cost for the production of the collective good benefit from their action if nobody else volunteers, but the cost is wasted if too many individuals volunteer. Increasing group size reduces the need of volunteering for each member of the group; the overall benefit for the group, however, decreases too because the larger the group is, the less likely it is that the collective good is produced. This problem persists even with a high degree of relatedness between group members; an optimal, intermediate group size exists that maximizes the probability to produce the collective good.     

The evolution of punishment and apology: an iterated prisoner's dilemma model

Recently, behaviors that seem to function as punishment or apology have been reported among non-human primates as well as humans. Such behaviors appear to play an important role in maintaining cooperation between individuals. Therefore, the evolution of these behaviors should be examined from the viewpoint of the evolution of cooperation. The iterated prisoner's dilemma (IPD) game is generally considered to be a standard model for the evolution of cooperation. In the present study, strategies accompanied by punishment-like attacks or apology-like behavior were introduced into the common IPD simulation. Punishment and apology were represented by the P signal and the AS signal given immediately after defection. A strategy with the P and AS signals, named the pPAS strategy, was proved to be an evolutionarily stable strategy under certain conditions. Numerical simulations were carried out according to different assigned values of the costs of punishment and apology. The simulations showed that pPAS could dominate the population (1) when the cost of giving P is relatively small, (2) when the cost of receiving P is relatively large, or (3) when the cost of giving AS is relatively large. The relative cost of giving AS had the clearest effect on the success of pPAS. pPAS can dominate the population even when a dominance asymmetry of the costs between two players was introduced. The present results suggest the possible evolution of social behaviors like punishment or apology as a means of maintaining cooperation. This revised version was published online in November 2006 with corrections to the Cover Date.     

Individual heterogeneity and costly punishment: a volunteer's dilemma

Social control and the enforcement of social norms glue a society together. It has been shown theoretically and empirically that informal punishment of wrongdoers fosters cooperation in human groups. Most of this research has focused on voluntary and uncoordinated punishment carried out by individual group members. However, as punishment is costly, it is an open question as to why humans engage in the punishment of wrongdoers even in one-time-only encounters. While evolved punitive preferences have been advocated as proximate explanations for such behaviour, the strategic nature of the punishment situation has remained underexplored. It has been suggested to conceive of the punishment situation as a volunteer''s dilemma (VOD), where only one individual''s action is necessary and sufficient to punish the wrongdoer. Here, we show experimentally that implementing the punishment situation as a VOD sustains cooperation in an environment where punishers and non-punishers coexist. Moreover, we show that punishment-cost heterogeneity allows individuals to tacitly agree on only the strongest group member carrying out the punishment, thereby increasing the effectiveness and efficiency of social norm enforcement. Our results corroborate that costly peer punishment can be explained without assuming punitive preferences and show that centralized sanctioning institutions can emerge from arbitrary individual differences.     

A simulation study of the effects of architectural constraints and resource translocation on population structure and competition in clonal plants

(1) Spatially explicit simulation of clonal plant growth is used to determine how ramet-level traits affect ramet density, spatial pattern of ramets and competitive ability of a clonal plant. The simulation model used combines elements of (i) an individual-based model of plant interactions, (ii) an architectural model of clonal plant growth, and (iii) a model of resource translocation within a set of physiologically integrated plant individuals. (2) The effects of two groups of parameters were studied: growth and resource acquisition parameters (resource accumulation, density-dependence of resource accumulation, resource translocation between ramets) and architectural rules (branching angle and probability of branching, internode length). The model was parameterised by values approximating those of clonally growing grasses as closely as possible. The basic parameter values were chosen from a short-turf grassland. Sensitivity analysis was carried out on relevant parameters around three basic points in the parameter space. Both single-species and two-species systems were studied. (3) It is shown that increasing resource acquisition and growth parameters increase ramet density, genet number and competitive ability. Translocation parameters and architectural parameters modify the effects of resource acquisition and growth, but their effect in single-species stands was smaller. (4) The simulations of species with fixed ramet sizes showed that ramet density in single-species stands cannot be used for predicting competitive ability. Increase in resource acquisition and growth parameters was correlated with an increase in equilibrium ramet density and competitive ability. Increasing branching angle, branching probability or internode length lead to an increased competitive ability, but did not affect equilibrium ramet density. Change of architectural parameters could therefore affect competitive ability independently of their effect on the final ramet density. (5) Spatial pattern both in single-species and two-species stands was also highly parameter-dependent. Changes in architectural parameters and in translocation usually lead to pronounced change in the spatial pattern; change in growth and resource acquisition parameters generally had little effect on spatial pattern.     

Demography and the tragedy of the commons

Individual success in group‐structured populations has two components. First, an individual gains by outcompeting its neighbours for local resources. Second, an individual's share of group success must be weighted by the total productivity of the group. The essence of sociality arises from the tension between selfish gains against neighbours and the associated loss that selfishness imposes by degrading the efficiency of the group. Without some force to modulate selfishness, the natural tendencies of self interest typically degrade group performance to the detriment of all. This is the tragedy of the commons. Kin selection provides the most widely discussed way in which the tragedy is overcome in biology. Kin selection arises from behavioural associations within groups caused either by genetical kinship or by other processes that correlate the behaviours of group members. Here, I emphasize demography as a second factor that may also modulate the tragedy of the commons and favour cooperative integration of groups. Each act of selfishness or cooperation in a group often influences group survival and fecundity over many subsequent generations. For example, a cooperative act early in the growth cycle of a colony may enhance the future size and survival of the colony. This time‐dependent benefit can greatly increase the degree of cooperation favoured by natural selection, providing another way in which to overcome the tragedy of the commons and enhance the integration of group behaviour. I conclude that analyses of sociality must account for both the behavioural associations of kin selection theory and the demographic consequences of life history theory.     

The influence of age and experience with conspecifics on territorial behavior inDrosophila melanogaster

Drosophila melanogastermales initiated aggressive behavior toward other males and defended territories several hours after they were able to court and mate females. Males that were 3 days or more posteclosion were more successful at holding territories than younger males. Three-day-old males established territories more readily and escalated more often against territory residents than males that were 1 day old. Residents did not usually force young males from territories until they were a few hours posteclosion. The development of territorial behavior was not affected by familiarity or prior exposure to females. Males held in isolation established territories more quickly and behaved more aggressively than males held in groups. Males that previously held territories were more likely to reestablish them after a disturbance.     

A glandular neckpatch secretion and vocalizations act as signals of territorial status in male puku (Kobus vardoni)

Territorial male puku ( Kobus vardoni ) have thicker necks than bachelors, develop a glandular secretion on their necks and utter bouts of whistles. The neckpatch develops at the time when bachelor males move into the territorial areas and when most conceptions occur. Interactions between two territorial males usually result in a face-off, whilst interactions between a bachelor male and a territorial male usually result in a chase. In both cases, the neckpatch may act as a territorial 'badge' which prevents escalation of the interaction.

Résumé

Le cob de Vardon mâle territorial a un cou plus épais que les mâles célibataires, développe une sécrétion glandulaire au niveau du cou et pousse de brefs siffle-ments. La glande du cou se développe à 1'époque ou les mâles célibataires pénètrent dans les espaces territoriaux, en saison de reproduction. Les interactions entre deux mâles territoriaux débouchent généralement sur un retrait tandis qu'entre un mâle célibataire et un mile territorial, elle aboutit d'habitude à une poursuite. Dans les deux cas, la glande du cou joue le rôle d'un 'badge' territorial qui empêche l'escalade de la confrontation.     

Absentee herd owners and part-time pastoralists: The political economy of resource use in northern Kenya

The prevalence of absentee herd ownership in Africa's pastoral areas is increasing. Its presence has important implications both for local resource management systems and for research programs that address pastoral ecology and related topics. This paper examines patterns of absentee herd ownership in the Baringo District of northern Kenya. This region has been the source of much debate regarding herder mismanagement of range lands. Three categories of absentee herd owners are discussed in the paper: (1) ranchers, (2) livestock traders, and (3) townsmen. It is suggested that the blame for some of the apparent resource mismanagement in the region may lie more with actors in these categories than with the pastoralists themselves. Data collected during an 18-month period in 1980–1981 on pastoral ecology, grazing patterns, and tenure institutions are presented in support of the argument. The paper concludes with a comparative analysis of contemporary resource management strategies in pastoral Africa, emphasizing that: (1) the Baringo case is not an isolated anomaly, and (2) a new orientation toward pastoral studies is warranted.     

The role of resource imbalances in the evolutionary ecology of tropical arboreal ants

In numbers and biomass, ants (Hymenoptera, Formicidae) often dominate arthropod faunas of tropical rainforest canopies. Extraordinary ant abundance is due principally to one or a few species able to tap the high productivity of canopy foliage by feeding on plant and homopteran exudates. Prior studies of nitrogen isotopic ratios show that exudate-feeders derive much of their nitrogen (N) by processing large quantities of N-poor, but carbohydrate (CHO)-rich, exudates. CHOs in excess of those that can be coupled with protein for growth and reproduction (postulated as the colony's first priorities) may be directed at little cost and some profit to functions that increase access to limiting protein. High dietary CHO:protein ratios for exudate-feeders appear to subsidize 'high tempo' foraging activity, defence of absolute (level III) territories, and production of N-free alarm/defence exocrine products that enhance ecological dominance in contests with other ants. Among organisms (e.g. plants and Lepidoptera) symbiotic with ants, CHO:protein ratios of ant rewards may control both the identities of ant associates and the quality of ant-rendered services. Dietary ratios of CHO:protein play an important and previously unrecognized role in the ecology and evolution of ants generally. Modifications of worker digestive systems in certain ant subfamilies and genera represent key innovations for handling and processing large volumes of liquid food. The supreme tropical dominants are species released from nest site limitation and able to place their nests in the vicinity of abundant exudate resources. Polydomy appears to be typical of these species and should produce energetic savings by taking colony fragments to the resource.