The Effects of Information on the Formation of Migration Routes and the Dynamics of Migration.

Most models of migration simply assume that migrants somehow make their way from their point of origin to their chosen destination. We know, however, that-especially in the case of asylum migration-the migrant journey often is a hazardous, difficult process where migrants make decisions based on limited information and under severe material constraints. Here we investigate the dynamics of the migration journey itself using a spatially explicit, agent-based model. In particular we are interested in the effects of limited information and information exchange. We find that under limited information, migration routes generally become suboptimal, their stochasticity increases, and migrants arrive much less frequently at their preferred destination. Under specific circumstances, self-organised consensus routes emerge that are largely unpredictable. Limited information also strongly reduces the migrants' ability to react to changes in circumstances. We conclude, first, that information and information exchange is likely to have considerable effects on all aspects of migration and should thus be included in future modelling efforts and, second, that there are many questions in theoretical migration research that are likely to profit from the use of agent-based modelling techniques.

Mapping secondary data gaps for social simulation modelling: A case study of Syrian asylum migration to Europe.

Simulation models of social processes may require data that are not readily available, have low accuracy, are incomplete or biased. The paper presents a formal process for collating, assessing, selecting, and using secondary data as part of creating, validating, and documenting an agent-based simulation model of a complex social process, in this case, asylum migration to Europe. The process starts by creating an inventory of data sources, and the associated metadata, followed by assessing different aspects of data quality according to pre-defined criteria. As a result, based on the typology of available data, we are able to produce a thematic map of the area under study, and assess the uncertainty of key data sources, at least qualitatively. We illustrate the process by looking at the data on Syrian migration to Europe in 2011-21. In parallel, successive stages of the development of a simulation model allow for identifying key types of information which are needed as input into empirically grounded modelling analysis. Juxtaposing the available evidence and model requirements allows for identifying knowledge gaps that need filling, preferably by collecting additional primary data, or, failing that, by carrying out a sensitivity analysis for the assumptions made. By doing so, we offer a way of formalising the data collection process in the context of model-building endeavours, while allowing the modelling to be predominantly question-driven rather than purely data-driven. The paper concludes with recommendations with respect to data and evidence, both for modellers, as well as model users in practice-oriented applications.

We can study migration with computer simulation models. The data we need for that may not be available or be low quality. This paper is about how to use data in modelling. We suggest how to gather the data, check their quality, and use them in models. We show how to find out where we need more data, and how to gather them in an inventory. We use an example of migration from Syria to Europe to point to different problems. How much we know about the data can help us understand what we know and do not know about migration.

Punish the thief-coevolution of defense and cautiousness stabilizes ownership.

ABSTRACT: Ownership of non-controllable resources usually has to be maintained by costly defense against competitors. Whether defense and thus ownership pays in terms of fitness depends on its effectiveness in preventing theft. We show that if the owners' willingness to defend varies in the population and information about it is available to potential thieves then the ability to react to this information and thus avoid being attacked by the owner is selected for. This can lead to a positive evolutionary feedback between cautiousness in intruders and aggressiveness in owners. This feedback can maintain ownership when the actual direct effectiveness of defense in reducing theft is very low or even absent, effectively turning defense into punishment. We conclude that the deterrence effect of defense in many situations could be stronger than that of prevention and that for many real-world scenarios the purpose of defense of resources might be to punish rather than to drive away intruders. SIGNIFICANCE STATEMENT: Many animals defend resources against conspecifics. Resource defense can usually only evolve if its costs are paid for by foiling attempts at theft. We show that if potential thieves can detect differences in aggressiveness between owners then cautious intruders and aggressive owners coevolve so that in the end even ineffective defense deters thieves and maintains ownership. This result greatly extends the number of situations in which we expect resource defense to evolve and has the potential to unify the concepts of defense and punishment.

What do territory owners defend against?

Theoretical research on evolutionary aspects of territoriality has a long history. Existing studies, however, differ widely in modelling approach and research question. A generalized view on the evolution of territoriality is accordingly still missing. In this review, we show that territorial conflicts can be classified into qualitatively distinct types according to what mode of access to a territory which competitor attempts to gain. We argue that many of the inconsistencies between existing studies can be traced back to the fact that, while using the same terminology, different instances of these types of conflicts have been investigated. We discuss the connections of each type of conflict to existing research within the wider area of animal conflicts. We conclude that a clear conceptual separation of different types of territorial conflicts is helpful but that a more general theory of territoriality has to account for interdependencies between them and that a more mechanistic approach to modelling territoriality is needed.

Correlations between sequential timing decisions do not necessarily indicate strategic behavior: a comment on Bêty et al.

Using correlation analysis, Bêty, Gauthier, and Giroux confirmed that individuals of the migrating snow geese (Chen caerulescens atlantica) arriving earlier on their breeding grounds experienced longer prelaying periods but laid earlier than late-arriving birds. They concluded that these birds strategically adjusted timing to optimize fitness. This test is, however, not sufficient to indicate strategic behavior. We show analytically that, without assuming strategic behavior, arrival date, prelaying period, and laying date are correlated with each other because of their sequential occurrence. We conclude that correlation tests on sequentially occurring variables are not sufficient to detect nonrandom relations.

Defence, intrusion and the evolutionary stability of territoriality.

Territorial behaviour can only be adaptive if its costs are outweighed by its benefits. Territorial individuals incur costs by defending their territories against intruders. Usually these intruders are assumed to be non-territorial floaters attempting to take over the whole territory or neighbours trying to extend the borders of their own territory. We instead investigate how costs and benefits of territorial behaviour are affected by neighbours which invade to steal resources on a territory. We show analytically that in the absence of defence intrusion into neighbouring territories always pays and that even if territories are defended intrusion levels can still be high. Using a more detailed simulation model we find that territory defence usually disappears from the population even if owners have a strong advantage over intruders in terms of fighting costs or foraging efficiency. Defence and thus territoriality can only be evolutionarily stable if fighting costs for the intruder relative to the productivity of the territory are very high or if crossing the borders between territories carries additional costs. Our results show that stealing of resources by neighbours can have a considerable effect on the evolutionary stability of territory defence and thus territoriality itself. A more mechanistic model of territorial behaviour is needed to incorporate these kinds of mechanisms into a general theory on the evolution of territoriality.