Patch depletion, niche structuring and the evolution of co-operative foraging

<p>Abstract</p> <p>Background</p> <p>Many animals live in groups. One proposed reason is that grouping allows cooperative food finding. Group foraging models suggest that grouping could increase food finding rates, but that such group processes could be evolutionarily unstable. These models assume discrete food patches which are fully detectable. However, often animals may only be able to perceive local parts of larger-scale environmental patterns. We therefore use a spatial individual-based model where food patches are aggregates of food items beyond the scale of individual perception. We then study the evolution of foraging and grouping behavior in environments with different resource distributions.</p> <p>Results</p> <p>Our results show that grouping can evolve to increase food intake rates. Two kinds of grouping evolve: traveling pairs and opportunistic grouping, where individuals only aggregate when feeding. Grouping evolves because it allows individuals to better sense and deplete patches. Such enhanced patch depletion is particularly apparent on fragmented and partially depleted patches, which are especially difficult for solitary foragers to deplete. Solitary foragers often leave a patch prematurely because a whole patch cannot be observed directly. In groups, individuals that are still eating allow other individuals that inadvertently leave the patch, to return and continue feeding. For this information sharing a grouping tendency is sufficient and observing whether a neighbor is eating is not necessary. Grouping therefore leads to a release from individual sensing constraints and a shift in niche specialization, allowing individuals to better exploit partially depleted patches.</p> <p>Conclusions</p> <p>The evolved group foraging can be seen as cooperative in the sense that it leads to a mutually-beneficial synergy: together individuals can achieve more than on their own. This cooperation exists as a group-level process generated by the interaction between grouping and the environment. Thus we reveal how such a synergy can originate in evolution as a side-effect of grouping via multi-level selection. Here there is no cooperative dilemma as individuals cannot avoid producing information for their neighbors. This scenario may be a useful starting point for studying the evolution of further social and cooperative complexity.</p

Consistent Strategy Updating in Spatial and Non-Spatial Behavioral Experiments Does Not Promote Cooperation in Social Networks

The presence of costly cooperation between otherwise selfish actors is not trivial. A prominent mechanism that promotes cooperation is spatial population structure. However, recent experiments with human subjects report substantially lower level of cooperation then predicted by theoretical models. We analyze the data of such an experiment in which a total of 400 players play a Prisoner's Dilemma on a 4 x 4 square lattice in two treatments, either interacting via a fixed square lattice (15 independent groups) or with a population structure changing after each interaction (10 independent groups). We analyze the statistics of individual decisions and infer in which way they can be matched with the typical models of evolutionary game theorists. We find no difference in the strategy updating between the two treatments. However, the strategy updates are distinct from the most popular models which lead to the promotion of cooperation as shown by computer simulations of the strategy updating. This suggests that the promotion of cooperation by population structure is not as straightforward in humans as often envisioned in theoretical models.This work has funding by the German Initiative of Excellence of the German Science Foundation (DFG). J.G.'s work was supported in part by The Ministerio de Ciencia e Innovacion (MICINN) (Spain) through grants PRODIEVO, MOSAICO, FPI, EEBB, and by Comunidad de Madrid (Spain) through grant MODELICO-CM). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Publicad

Local Orientation and the Evolution of Foraging: Changes in Decision Making Can Eliminate Evolutionary Trade-offs

Information processing is a major aspect of the evolution of animal behavior. In foraging, responsiveness to local feeding opportunities can generate patterns of behavior which reflect or “recognize patterns” in the environment beyond the perception of individuals. Theory on the evolution of behavior generally neglects such opportunity-based adaptation. Using a spatial individual-based model we study the role of opportunity-based adaptation in the evolution of foraging, and how it depends on local decision making. We compare two model variants which differ in the individual decision making that can evolve (restricted and extended model), and study the evolution of simple foraging behavior in environments where food is distributed either uniformly or in patches. We find that opportunity-based adaptation and the pattern recognition it generates, plays an important role in foraging success, particularly in patchy environments where one of the main challenges is “staying in patches”. In the restricted model this is achieved by genetic adaptation of move and search behavior, in light of a trade-off on within- and between-patch behavior. In the extended model this trade-off does not arise because decision making capabilities allow for differentiated behavioral patterns. As a consequence, it becomes possible for properties of movement to be specialized for detection of patches with more food, a larger scale information processing not present in the restricted model. Our results show that changes in decision making abilities can alter what kinds of pattern recognition are possible, eliminate an evolutionary trade-off and change the adaptive landscape

Human cooperative behavior

Summary Evolutionary theory provides the biological sciences, with a fundamental and powerful model to explain the emergence of cooperative behavior. A detailed explanation for the existence of cooperation between related individuals is provided by the theory of kin selection. When kin cooperate the helper gives the receiver an advantage and thereby increases the relative probability that copies of his own genes are present in the next generations. However, one cannot explain examples of apparent altruism through kin selection, because in these cases unrelated individuals interact. The answer for many of these examples is provided by the theory of reciprocal altruism, where individuals behave reciprocal by returning help to a previous donor. By applying these two theories it is possible to explain many, but by far not all cooperative situations. There have to be other mechanisms that lead to cooperation and sustain already established cooperation. In my dissertation I have tested empirically new models and predictions of how cooperation between unrelated humans can be established. This research is especially important because we interact in a close net of relationships, where cooperation between unrelated individuals plays one of the main roles. Modern human societies are impossible to imagine without cooperation between unrelated individuals. By identifying the circumstances under which cooperation is stable between unrelated individuals, it will be possible to understand the deciding factors in politics, economy and in our private lives. As a consequence we would be provided with intellectual tools to positively influence the deciding factors by alternating the circumstances accordingly. We are often not aware of the importance of cooperation between unrelated partners in our daily lives. Regularly people find unconsciously cooperative solutions, for instance when they try simultaneously to walk through a narrow door. Some professions depend very strongly on cooperative behavior between unrelated colleagues. To act uncooperatively in such a profession can endanger the health or even the lives of the colleagues (e.g. firemen and firewoman). Cooperative strategies for these kinds of situations have to have evolved and need to be evolutionary stable, otherwise we would hardly ever find cooperative behavior in the present and then only between related individuals. According to the evolutionary theory the cooperative strategies found today, also have to provide an advantage to the bearer. For a long time economists and biologists have been interested in the emergence and sustainability of cooperative behavior. Nevertheless, only with the introduction of game theory, a mathematical basis was established to incorporate this behavior into biological evolutionary models. From then on it was possible to make predictions with the help of theoretical models, about the circumstances under which certain behavioral patterns emerge and what underlying mechanisms possibly sustain these patterns. In my dissertation I have empirically tested predictions of circumstances that promote cooperative behavior between unrelated humans. The main results of my work are the following: (i) Humans often donate money to charity. On first sight this seems to be a disadvantageous behavioral trait. Donations to charity include costs that reduce the direct fitness of the individual. However, it has to be beneficial to the bearer, otherwise it would be eliminated from the population through evolutionary processes. The study showed that there is indeed an advantage. By donating money to charity (here to UNICEF) one builds up a good personal reputation in the own social group. Participants that donated to UNICEF received with higher probability help from other participants and were as well more likely to be voted the group representative. (ii) Reputation is known to be an important currency in indirect reciprocity games. Humans therefore should also try to establish a good reputation in other social games, when this reputation is known in future indirect reciprocity games. Humans are in general unable to sustain a public resource that everybody is free to overuse anonymously. Is it possible that humans sustain a public resource if the use of the resource is linked to the personal reputation? The experiment showed, that the risk of loosing a good reputation by overusing the public resource actually lead to sustaining it. Furthermore the public resource was not only sustained, but also turned out to be surprisingly profitable to all group members. (iii) A theoretical model supplied a new possibility to sustain a public resource and hereby make humans act cooperatively. The strikingly simple idea was to introduce the possibility not to participate in the public goods group and instead use a personal resource with a low but sure payoff. The prediction was an always recurring rise to dominance, of three strategies ((a) not to participate in the public goods group, (b) participate in the public goods group and to cooperate within the group or (c) participate and to defect within the group) within the population. This dynamic was expected because whenever most members of the population choose the same strategy, one of the other two strategies had a higher payoff. The same type as the predicted dynamic has also been found in models of the famous children game of “rock-paper-scissors”. The model predicted that the public resource is sustained by the ongoing dynamic, which is liked with a recurring rise of cooperative behavior. Is it enough to supply humans with the possibility not to participate in the public goods game to produce such recurring rise of cooperation? The dynamic was established as predicted, whereby the changing dominance of the three strategies with repeated cooperative phases could be observed and the resource was on average sustained. (iv) When humans make decisions about using a public resource, which at some times are reputation relevant and at other times are not reputation relevant, do they use this information strategically? In this study it was shown that, humans are aware when their decisions are not reputation relevant and immediately reduce their cooperation to maximize their personal profit. Once more, as soon as the decisions about using the public resource were linked to the reputation, cooperation was much higher and the resource was sustained. (v) In some potentially cooperative situations humans’ meet partners from outside the own social group. These “strangers” have a reputation that they have built in another social group. Do humans put a different value on a strangers’ reputation in comparison to the reputation of members of the own social group? It was shown that it is not relevant if the reputation was built within the own or in a foreign social group. In summary we found the following: Humans behave uncooperatively, when it is to the personal advantage. However, certain circumstances lead to cooperative behavior in humans. Reputation building is one of the most important mechanisms in this context, which enables us to cooperate even with not related strangers. However humans consciously make strategic use of situations where they do not harm their reputation by behaving uncooperatively. Nevertheless, even in completely anonymous situations it is possible to create circumstances, like introducing optional participation in the public goods situations, which promote cooperative behavior in humans.Contents Summary 7 Zusammenfassung 11 Introduction 1 Cooperation 17 2 Game Theory 18 3 General approach to testing 20 4 Thesis outline 23 Chapters I Donors to charity gain in both indirect reciprocity and political 29 reputation II Reputation helps solve the 'tragedy of the commons' 37 III Volunteering leads to rock-paper-scissors dynamics in a public 47 goods game IV A human cooperation strategy that is conditional on being 59 recognized in other situations V Reputation is valuable inside and outside the own social group 69 Conclusion 81 Danksagung 83 References 85 Glossary 91 Appendix 93 Curriculum vitae 99 Erklärung 10

Reputation helps solve the ''tragedy of the commons''

The problem of sustaining a public resource that everybody is free to overuse-the ''tragedy of the commons''(1-7)-emerges in many social dilemmas, such as our inability to sustain the global climate. Public goods experiments(4), which are used to study this type of problem, usually confirm that the collective benefit will not be produced. Because individuals and countries often participate in several social games simultaneously, the interaction of these games may provide a sophisticated way by which to maintain the public resource. Indirect reciprocity(8), ''give and you shall receive'', is built on reputation and can sustain a high level of cooperation, as shown by game theorists(9-11). Here we show, through alternating rounds of public goods and indirect reciprocity games, that the need to maintain reputation for indirect reciprocity maintains contributions to the public good at an unexpectedly high level. But if rounds of indirect reciprocation are not expected, then contributions to the public good drop quickly to zero. Alternating the games leads to higher profits for all players. As reputation may be a currency that is valid in many social games, our approach could be used to test social dilemmas for their solubility

Donors to charity gain in both indirect reciprocity and political reputation.

Darwinian evolution can explain human cooperative behaviour among non-kin by either direct or indirect reciprocity. In the latter case one does not expect a return for an altruistic act from the recipient as with direct reciprocity, but from another member of the social group. However, the widespread human behaviour of donating to poor people outside the social group, for example, to charity organizations, that are unlikely to reciprocate indirectly and thus are equivalent to defectors in the game is still an evolutionary puzzle. Here we show experimentally that donations made in public to a well-known relief organization resulted both in increased income (that the donors received from the members of their group) and in enhanced political reputation (they were elected to represent the interests of their group). Donations may thus function as an honest signal for one's social reliability

Strategic Spatial Planning in European City-Regions: Parallel Processes or Divergent Trajectories? (NIRSA) Working Paper Series No. 60

Drawing on recent experiences of strategic spatial planning in two city-regions in Europe, the paper seeks to challenge dominant narratives of the emergence of strategic spatial planning as a uni-dimensional process of policy convergence. Recognising a need for fine-grained analysis of practices of spatial planning in diverse territorial and institutional contexts, the paper presents a framework for contextualised comparative analysis, identifying multiple levels of differentiation. The application of this comparative framework is subsequently illustrated with reference to the two city-regions of Dublin and Erfurt. The paper concludes with an outline of an agenda for further research