| 1. |
- Enfjäll, Karin, et al.
(författare)
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The evolution of dispersal - the importance of information about population density and habitat characteristics
- 2009
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Ingår i: Oikos. - : Wiley. - 0030-1299 .- 1600-0706. ; 118, s. 291-299
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of mobility patterns and dispersal strategies depend on different population, habitat and life history characteristics. The ability to perceive and make use of information about the surrounding environment for dispersal decisions will also differ between organisms. To investigate the evolutionary consequences of such differences, we have used a simulation model with nearest-neighbour dispersal in a metapopulation to study how variation in the ability to obtain and make use of information about habitat quality and conspecific density affects the evolution of dispersal strategies. We found a rather strong influence of variation in information on the overall rate of dispersal in a metapopulation. The highest emigration rate evolved in organisms with no information about either density or habitat quality and the lowest rate was found in organisms with information about both the natal and the neighbouring patches. For organisms that can make use of information about conspecific density, positively density-dependent dispersal evolved in the majority of cases, with the strongest density dependence occurring when an individual only has information about density in the natal patch. However, we also identified situations, involving strong local population fluctuations and frequent local extinctions, where negatively density-dependent dispersal evolved.
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| 2. |
- Leimar, Olof, 1949-, et al.
(författare)
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Behavioural specialization and learning in social networks
- 2022
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 289:1980
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Tidskriftsartikel (refereegranskat)abstract
- Interactions in social groups can promote behavioural specialization. One way this can happen is when individuals engage in activities with two behavioural options and learn which option to choose. We analyse interactions in groups where individuals learn from playing games with two actions and negatively frequency-dependent payoffs, such as producer–scrounger, caller–satellite, or hawk–dove games. Group members are placed in social networks, characterized by the group size and the number of neighbours to interact with, ranging from just a few neighbours to interactions between all group members. The networks we analyse include ring lattices and the much-studied small-world networks. By implementing two basic reinforcement-learning approaches, action–value learning and actor–critic learning, in different games, we find that individuals often show behavioural specialization. Specialization develops more rapidly when there are few neighbours in a network and when learning rates are high. There can be learned specialization also with many neighbours, but we show that, for action–value learning, behavioural consistency over time is higher with a smaller number of neighbours. We conclude that frequency-dependent competition for resources is a main driver of specialization. We discuss our theoretical results in relation to experimental and field observations of behavioural specialization in social situations.
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| 3. |
- Leimar, Olof, 1949-, et al.
(författare)
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Effects of local versus global competition on reproductive skew and sex differences in social dominance behaviour
- 2022
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Ingår i: Proceedings of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 289:1987
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Tidskriftsartikel (refereegranskat)abstract
- Social hierarchies are often found in group-living animals. The hierarchy position can influence reproductive success (RS), with a skew towards high-ranking individuals. The amount of aggression in social dominance varies greatly, both between species and between males and females within species. Using game theory we study this variation by taking into account the degree to which reproductive competition in a social group is mainly local to the group, emphasizing within-group relative RS, or global to a larger population, emphasizing an individual's absolute RS. Our model is similar to recent approaches in that reinforcement learning is used as a behavioural mechanism allowing social-hierarchy formation. We test two hypotheses. The first is that local competition should favour the evolution of mating or foraging interference, and thus of reproductive skew. Second, decreases in reproductive output caused by an individual's accumulated fighting damage, such as reduced parenting ability, will favour less intense aggression but should have little influence on reproductive skew. From individual-based simulations of the evolution of social dominance and interference, we find support for both hypotheses. We discuss to what extent our results can explain observed sex differences in reproductive skew and social dominance behaviour.
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| 4. |
- Leimar, Olof, 1949-
(författare)
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Environmental and genetic cues in the evolution of phenotypic polymorphism
- 2009
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Ingår i: Evolutionary Ecology. - : Springer Science and Business Media LLC. - 0269-7653 .- 1573-8477. ; 23, s. 125-135
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Tidskriftsartikel (refereegranskat)abstract
- Phenotypic polymorphism is a consequence of developmental plasticity, in which the trajectories of developing organisms diverge under the influence of cues. Environmental and genetic phenotype determination are the two main categories of polymorphic development. Even though both may evolve as a response to varied environments, they are traditionally regarded as fundamentally distinct phenomena. They can however be joined into a single framework that emphasizes the parallel roles of environmental and genetic cues in phenotype determination. First, from the point of view of immediate causation, it is common that phenotypic variants can be induced either by environmental or by allelic variation, and this is referred to as gene-environment interchangeability. Second, from the point of view of adaptation, genetic cues in the form of allelic variation at polymorphic loci can play similar roles as environmental cues in providing information to the developmental system about coming selective conditions. Both types of cues can help a developing organism to fit its phenotype to selective circumstances. This perspective of information in environmental and genetic cues can produce testable hypotheses about phenotype determination, and can thus increase our understanding of the evolution of phenotypic polymorphism.
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| 5. |
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| 6. |
- Leimar, Olof, 1949-, et al.
(författare)
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Flexible learning in complex worlds
- 2024
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Ingår i: Behavioral Ecology. - 1045-2249 .- 1465-7279. ; 35:1
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Tidskriftsartikel (refereegranskat)abstract
- Cognitive flexibility can enhance the ability to adjust to changing environments. Here, we use learning simulations to investigate the possible advantages of flexible learning in volatile (changing) environments. We compare two established learning mechanisms, one with constant learning rates and one with rates that adjust to volatility. We study an ecologically relevant case of volatility, based on observations of developing cleaner fish Labroides dimidiatus that experience a transition from a simpler to a more complex foraging environment. There are other similar transitions in nature, such as migrating to a new and different habitat. We also examine two traditional approaches to volatile environments in experimental psychology and behavioral ecology: reversal learning, and learning set formation (consisting of a sequence of different discrimination tasks). These provide experimental measures of cognitive flexibility. Concerning transitions to a complex world, we show that both constant and flexible learning rates perform well, losing only a small proportion of available rewards in the period after a transition, but flexible rates perform better than constant rates. For reversal learning, flexible rates improve the performance with each successive reversal because of increasing learning rates, but this does not happen for constant rates. For learning set formation, we find no improvement in performance with successive shifts to new stimuli to discriminate for either flexible or constant learning rates. Flexible learning rates might thus explain increasing performance in reversal learning but not in learning set formation, and this can shed light on the nature of cognitive flexibility in a given system. Animals need to adjust to changes that occur in their environment, such as new food types becoming available or old food types becoming unsuitable. Learning about these changes could be essential for success, in particular, if the environment is complex, with many things to learn about. When changes happen, it might be advantageous to quickly learn about new things. We use computer simulations of learning to investigate how big the advantage might be.
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| 7. |
- Leimar, Olof, 1949-, et al.
(författare)
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Game theory in biology : 50 years and onwards
- 2023
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Ingår i: Philosophical Transactions of the Royal Society of London. Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 378:1876
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Forskningsöversikt (refereegranskat)abstract
- Game theory in biology gained prominence 50 years ago, when Maynard Smith & Price formulated the concept of an evolutionarily stable strategy (ESS). Their aim was to explain why conflicts between animals of the same species usually are of a ‘limited war’ type, not causing serious injury. They emphasized that game theory is an alternative to previous ideas about group selection, which were used by ethologists to explain limited aggression. Subsequently, the ESS concept was applied to many phenomena with frequency dependence in the evolutionary success of strategies, including sex allocation, alternative mating types, contest behaviour and signalling, cooperation, and parental care. Both the analyses of signalling and cooperation were inspired by similar problems in economics and attracted much attention in biology. Here we give a perspective on which of the ambitions in the field have been achieved, with a focus on contest behaviour and cooperation. We evaluate whether the game-theoretical study of the evolution of cooperation has measured up to expectations in explaining the behaviour of non-human animals. We also point to potentially fruitful directions for the field, and emphasize the importance of incorporating realistic behavioural mechanisms into models.
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| 8. |
- Leimar, Olof, 1949-
(författare)
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Multidimensional convergence stability
- 2009
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Ingår i: Evolutionary Ecology Research. - 1522-0613 .- 1937-3791. ; 11, s. 191-208
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Tidskriftsartikel (refereegranskat)abstract
- Questions: Are there general stability conditions for the evolution Of Multidimensional traits, regardless of genetic correlations between traits? Can genetic correlations influence whether evolution converges to a stable trait vector? Mathematical methods: Adaptive dynamics theory and the weak selection limit of quantitative genetics. Key assumptions: Evolutionary change is represented as either (i) any gradualistic adaptive path in trait space, consisting of a sequence of small-effect mutant invasions, allowing for pleiotropic mutants, or (ii) a solution to the 'canonical equation' of adaptive dynamics with a gradually varying mutational covariance matrix. Assumption (ii) is a special case of (i). Conclusions: It is possible to formulate robust stability conditions for multidimensional traits, but most evolutionary equilibria will not satisfy these conditions. Under the liberal assumption (i), there will in general be no 'absolutely convergence stable' equilibria in multidimensional trait spaces (except for simplified models). Under the more restrictive assumption (ii), a Much larger proportion of evolutionary equilibria is 'strongly convergence stable', i.e. are stable irrespective of genetic correlations.
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| 9. |
- Leimar, Olof, 1949-, et al.
(författare)
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Reproductive skew, fighting costs and winner-loser effects in social dominance evolution
- 2022
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Ingår i: Journal of Animal Ecology. - : Wiley. - 0021-8790 .- 1365-2656. ; 91:5, s. 1036-1046
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Tidskriftsartikel (refereegranskat)abstract
- Social hierarchies are often found in group-living animals and can be formed through pairwise aggressive interactions. The dominance rank can influence reproductive success (RS) with a skew towards high-ranking individuals.Using game theory, we investigate how the opportunity for differently ranked individuals to achieve RS influences the costs of hierarchy formation and the strength of winner and loser effects.In our model, individuals adjust their aggressive and submissive behaviour towards others through reinforcement learning. The learning is based on rewards and penalties, which depend on relative fighting ability. From individual-based simulations, we determine evolutionary equilibria of traits such as learning rates. We examine situations that differ in the extent of monopolisation of contested RS by dominants and in the proportion of total RS that is contested.The model implements two kinds of fighting costs: a decrease in effective fighting ability from damage (loss of condition) and a risk of mortality that increases with the total accumulated damage. Either of these costs can limit the amount of fighting.We find that individuals form stable dominance hierarchies, with a positive correlation between dominance position and fighting ability. The accumulated costs differ between dominance positions, with the highest costs paid by low or intermediately ranked individuals. Costs tend to be higher in high-skew situations.We identify a ‘stay-in, opt-out’ syndrome, comprising a range from weaker (stay-in) to stronger (opt-out) winner–loser effects. We interpret the opt-out phenotype to be favoured by selection on lower ranked individuals to opt out of contests over social dominance, because it is more pronounced when more of the total RS is uncontested.We discuss our results in relation to field and experimental observations and argue that there is a need for empirical investigation of the behaviour and reproductive success of lower ranked individuals.
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| 10. |
- Leimar, Olof, 1949-, et al.
(författare)
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Social bond dynamics and the evolution of helping
- 2024
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - 0027-8424 .- 1091-6490. ; 120:11
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Tidskriftsartikel (refereegranskat)abstract
- Empiricists often struggle to apply game theory models to real-life cases of animal cooperation. One reason is that many examples of cooperation occur in stable groups, where individuals form social bonds that influence exchanges of help in ways that are not well described by previous models, including the extent of reciprocity and how relationships are initiated. We present a game theory model exploring the conditions under which social bonds between group members promote cooperation. In the model, bonds build up from exchanges of help in a similar way as the strength of association increases in learning, as in the Rescorla–Wagner rule. The bonds in turn affect partner choice and influence helping amounts. The model has a mechanism of reciprocity for bonded pairs, which can evolve toward either loose or strict reciprocation. Several aspects of the model are inspired by observations of food sharing in vampire bats. We find that small social neighborhoods are required for the evolutionary stability of helping, either as small group sizes, or if bonded members of larger groups can form temporary (daily) smaller groupings. The costs of helping need to be fairly low, while the benefits can be substantial. The form of reciprocity that evolves is neither immediate nor very strict. Individuals in need request help based on bond strength, but there is also an evolved preference for initiating bonds with new group members. In contrast, if different groups come into temporary contact, the evolved tendency is to avoid forming bonds between groups.
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