Prof. Dr. Stefan Krause

Position Professor


Lübeck University of Applied Sciences, Electrical Engineering and Computer Science
Stefan Krause
Mönkhofer Weg 239
D-23562 Lübeck, Germany
Room: 18-0.21

Phone +49 (0)451 300-5315

Research Interests

The main focus of my research is on

  • analysis and modelling of collective behaviour and collective intelligence in humans and animals
  • analysis and modelling of social structures (social networks) in animals and humans
  • the application of results of research in these fields to problems in technical and organisational areas

Curriculum Vitae

  • Since 2006 Professor of Computer Science, Lübeck University of Applied Sciences
  • 2000 - 2005 Member of Working Groups of the World Wide Web Consortium (Voice Browser, Multimodal Interaction)
  • 1999 - 2005 Research and Development in the field of speech recognition at Philips Speech Processing GmbH and ScanSoft GmbH in Aachen, Germany
  • 1993 - 1998 Research and Development in the field of adaptive traffic control at Ingenieurbüro Dr. Brenner + Münnich in Berlin, Germany
  • 1992 Doctorate (Dr.-Ing.) in Computer Science, Technical University Berlin
  • 1988 - 1992 Research Assistant at the Technical University Berlin, Department of Computer Science
  • 1988 Diploma in Computer Science, Technical University Berlin, Department of Computer Science
  • Born 1962 in Berlin

Teaching Activities

My main teaching areas are

  • Computer programming
  • Software engineering
  • Artificial intelligence

Talks and Workshops

(Format: Event  /  Location  /  Organiser  /  Date)

  • Seminar on swarm intelligence at the Summer University Villigst  /  Schwerte  /  Evangelisches Studienwerk Villigst  /  August 2017
  • Workshop on swarm intelligence  /  Geseke-Eringerfeld  /  Cusanuswerk  /  May 2015
  • Advanced training course "Neue Entwicklungen in der psychosomatischen Medizin und Psychotherapie"  /   Berus  /   AHG Klinik Berus  /   March 2013
  • Workshop "Animal Social Networks: Perspectives and Challenges"  /   Bielefeld  /   Center for Interdisciplinary Research, University of Bielefeld  /   August 2012
  • "LzO-Blickpunkte"  /   Oldenburg  /   Landessparkasse zu Oldenburg  /   May 2012
  • Congress "Health on Top"  /   Petersberg  /   Skolamed GmbH  /   March 2012
  • Summer academy, working group "Swarm intelligence in humans and animals" / Nizza (La Colle-sur-Loup) / Studienstiftung des deutschen Volkes / September 2011
  • Diskurs Zukunft: "Weisheit der Vielen"  /   Wolfsburg  /   Dept. Future Research & Trend Transfer, Volkswagen AG  /   May 2011
  • Meeting of the Young Professionals  /   Bremen  /   Verband Beratender Ingenieure  /   February 2011
  • Management Workshop 2011  /   Salzburg  /   Porsche Holding GmbH  /   January&February 2011
  • Workshop "Zukunft ist das Ziel, Neugier der Motor – Energieeffizient mit Bionik"  /   Lübeck  /   IHK Lübeck  /   November 2010
  • Research colloquium "Animal Social Networks"  /   Berlin  /   Freie Universität Berlin  /   November 2010
  • 2nd Sustainable Summer School  /   Cologne  /   Bergische Universität Wuppertal + Folkwang University of the Arts + others  /   August 2010
  • "Humboldt unterwegs - Die Stadt als Campus"  /   Berlin, Alexanderplatz  /   Humboldt Universität Berlin  /   May 2010
  • Conference of the Association for the Study of Animal Behaviour  /   Exeter  /   University of Exeter  /   April 2010
  • Workshop "Animal Social Networks – methods and models"  /   Bath  /   University of Bath  /   July 2009
  • Conference "Darwin meets Business"  /   Botanischer Garten Berlin  /   Dr. Otto Training & Consulting + BIOKON  /   June 2009
  • Seminar Industrial Design  /   Berlin  /   UdK Berlin  /   May 2009


see also Google Scholar profile Stefan Krause

Refereed Articles and Book Chapters
[2021] Causal evidence for the adaptive benefits of social foraging in the wild (Lysanne Snijders, Stefan Krause, Alan N. Tump, Michael Breuker, Chente Ortiz, Sofia Rizzi, Indar W. Ramnarine, Jens Krause, Ralf H.J.M. Kurvers), In Communications Biology, 2021. [bib] [pdf] [abstract]
Sociality is a fundamental organizing principle across taxa, thought to come with a suite of adaptive benefits. However, making causal inferences about these adaptive benefits requires experimental manipulation of the social environment, which is rarely feasible in the field. Here we manipulated the number of conspecifics in Trinidadian guppies (Poecilia reticulata) in the wild, and quantified how this affected a key benefit of sociality, social foraging, by investigating several components of foraging success. As adaptive benefits of social foraging may differ between sexes, we studied males and females separately, expecting females, the more social and risk-averse sex in guppies, to benefit more from conspecifics. Conducting over 1600 foraging trials, we found that in both sexes, increasing the number of conspecifics led to faster detection of novel food patches and a higher probability of feeding following detection of the patch, resulting in greater individual resource consumption. The extent of the latter relationship differed between the sexes, with males unexpectedly exhibiting a stronger social benefit. Our study provides rare causal evidence for the adaptive benefits of social foraging in the wild, and highlights that sex differences in sociality do not necessarily imply an unequal ability to profit from the presence of others.
[2020] An interaction mechanism for the maintenance of fission–fusion dynamics under different individual densities (David Bierbach, Stefan Krause, Pawel Romanczuk, Juliane Lukas, Lenin Arias-Rodriguez, Jens Krause), In PeerJ, 2020. [bib] [pdf] [abstract]
Animals often show high consistency in their social organisation despite facing changing environmental conditions. Especially in shoaling fish, fission–fusion dynamics that describe for which periods individuals are solitary or social have been found to remain unaltered even when density changed. This compensatory ability is assumed to be an adaptation towards constant predation pressure, but the mechanism through which individuals can actively compensate for density changes is yet unknown. The aim of the current study is to identify behavioural patterns that enable this active compensation. We compared the fission–fusion dynamics of two populations of the live-bearing Atlantic molly (Poecilia mexicana) that live in adjacent habitats with very different predator regimes: cave mollies that inhabit a low-predation environment inside a sulfidic cave with a low density of predatory water bugs (Belostoma sp.), and mollies that live directly outside the cave (henceforth called “surface” mollies) in a high-predation environment. We analysed their fission–fusion dynamics under two different fish densities of 12 and 6 fish per 0.36 m2. As expected, surface mollies spent more time being social than cave mollies, and this difference in social time was a result of surface mollies being less likely to discontinue social contact (once they had a social partner) and being more likely to resume social contact (once alone) than cave mollies. Interestingly, surface mollies were also less likely to switch among social partners than cave mollies. A random walk simulation predicted each population to show reduced social encounters in the low density treatment. While cave mollies largely followed this prediction, surface mollies maintained their interaction probabilities even at low density. Surface mollies achieved this by a reduction in the size of a convex polygon formed by the group as density decreased. This may allow them to largely maintain their fission–fusion dynamics while still being able to visit large parts of the available area as a group. A slight reduction (21%) in the area visited at low densities was also observed but insufficient to explain how the fish maintained their fission–fusion dynamics. Finally, we discuss potential movement rules that could account for the reduction of polygon size and test their performance.
[2020] Linking hunting weaponry to attack strategies in sailfish and striped marlin (Matthew J. Hansen, Stefan Krause, Michael Breuker, Ralf H. J. M. Kurvers, Félicie Dhellemmes, Paul E. Viblanc, Johannes Müller, Kristin Mahlow, Kevin Boswell, Stefano Marras, Paolo Domenici, Alexander D. M. Wilson, James E. Herbert-Read, John F. Steffensen, Guido Fritsch, Thomas B. Hildebrandt, Paul Zaslansky, Pascal Bach, Philippe S. Sabarros, Jens Krause), In Proceedings of the Royal Society B: Biological Sciences, The Royal Society, 2020. [bib] [pdf] [abstract]
Linking morphological differences in foraging adaptations to prey choice and feeding strategies has provided major evolutionary insights across taxa. Here, we combine behavioural and morphological approaches to explore and compare the role of the rostrum (bill) and micro-teeth in the feeding behaviour of sailfish (Istiophorus platypterus) and striped marlin (Kajikia audax) when attacking schooling sardine prey. Behavioural results from high-speed videos showed that sailfish and striped marlin both regularly made rostrum contact with prey but displayed distinct strategies. Marlin used high-speed dashes, breaking schools apart, often contacting prey incidentally or tapping at isolated prey with their rostra; while sailfish used their rostra more frequently and tended to use a slower, less disruptive approach with more horizontal rostral slashes on cohesive prey schools. Capture success per attack was similar between species, but striped marlin had higher capture rates per minute. The rostra of both species are covered with micro-teeth, and micro-CT imaging showed that species did not differ in average micro-tooth length, but sailfish had a higher density of micro-teeth on the dorsal and ventral sides of their rostra and a higher amount of micro-teeth regrowth, suggesting a greater amount of rostrum use is associated with more investment in micro-teeth. Our analysis shows that the rostra of billfish are used in distinct ways and we discuss our results in the broader context of relationships between morphological and behavioural feeding adaptations across species.
[2019] Females facilitate male food patch discovery in a wild fish population (Lysanne Snijders, Ralf H. J. M. Kurvers, Stefan Krause, Alan N. Tump, Indar W. Ramnarine, Jens Krause), In Journal of Animal Ecology, 2019. [bib] [pdf] [abstract]
1. Responding to the information provided by others is an important foraging strategy in many species. Through social foraging, individuals can more efficiently find unpredictable resources and thereby increase their foraging success. 2. When individuals are more socially responsive to particular phenotypes than others, however, the advantage they obtain from foraging socially is likely to depend on the phenotype composition of the social environment. We tested this hypothesis by performing experimental manipulations of guppy, Poecilia reticulata, sex compositions in the wild. 3. Males found fewer novel food patches in the absence of females than in mixed-sex compositions, while female patch discovery did not differ regardless of the presence or absence of males. 4. We argue that these results were driven by sex-dependent mechanisms of social association: Markov chain-based fission-fusion modelling revealed that less social individuals found fewer patches and that males reduced sociality when females were absent. In contrast, females were similarly social with or without males. 5. Our findings highlight the relevance of considering how individual and population-level traits interact in shaping the advantages of social foraging in the wild.
[2018] Individual- and population-level drivers of consistent foraging success across environments (Lysanne Snijders, Ralf H. J. M. Kurvers, Stefan Krause, Indar W. Ramnarine, Jens Krause), In Nature Ecology & Evolution, 2018. [bib] [pdf] [abstract]
Individual foraging is under strong natural selection. Yet, whether individuals differ consistently in their foraging success across environments, and which individual- and population-level traits might drive such differences, is largely unknown. We addressed this question in a field experiment, conducting over 1,100 foraging trials with subpopulations of guppies, Poecilia reticulata, translocated across environments in the wild. We show that individuals consistently differed in reaching and acquiring food resources, but not control ‘resources’, across environments. Social individuals reached and acquired more food resources than less-social ones and males reached more food resources than females. Yet, overall, individuals were more likely to join females at resources than males, which might explain why individuals in subpopulations with relatively more females reached and acquired, on average, more food resources. Our results provide rare evidence for individual differences in foraging success across environments, driven by individual- and population-level (sex ratio) traits.
[2017] Injury-mediated decrease in locomotor performance increases predation risk in schooling fish (Jens Krause, James E. Herbert-Read, Frank Seebacher, Paolo Domenici, Alexander D. M. Wilson, Stefano Marras, Morten B. S. Svendsen, Daniel Strömbom, John F. Steffensen, Stefan Krause, Paul E. Viblanc, Pierre Couillaud, Pascal Bach, Philippe S. Sabarros, Paul Zaslansky, Ralf H. J. M. Kurvers), In Philosophical Transactions of the Royal Society B: Biological Sciences, The Royal Society, 2017. [bib] [abstract]
The costs and benefits of group living often depend on the spatial position of individuals within groups and the ability of individuals to occupy preferred positions. For example, models of predation events for moving prey groups predict higher mortality risk for individuals at the periphery and front of groups. We investigated these predictions in sardine (Sardinella aurita) schools under attack from group hunting sailfish (Istiophorus platypterus) in the open ocean. Sailfish approached sardine schools about equally often from the front and rear, but prior to attack therewas a chasing period in which sardines attempted to swim away from the predator. Consequently, all sailfish attacks were directed at the rear and peripheral positions of the school, resulting in higher predation risk for individuals at these positions. During attacks, sailfish slash at sardines with their bill causing prey injury including scale removal and tissue damage. Sardines injured in previous attacks were more often found in the rear half of the school than in the front half. Moreover, injured fish had lower tail-beat frequencies and lagged behind uninjured fish. Injuries inflicted by sailfish bills may, therefore, hinder prey swimming speed and drive spatial sorting in prey schools through passive self-assortment. We found only partial support for the theoretical predictions from current predator–prey models, highlighting the importance of incorporating more realistic predator–prey dynamics into these models. This article is part of the themed issue ‘Physiological determinants of social behaviour in animals’.
[2016] The evolution of lateralization in group hunting sailfish (Ralf H. J. M. Kurvers, Stefan Krause, Paul E. Viblanc, James E. Herbert-Read, Paul Zaslansky, Paolo Domenici, Stefano Marras, John F. Steffensen, Morten B. S. Svendsen, Alexander D. M. Wilson, Pierre Couillaud, Kevin M. Boswell, Jens Krause), In Current Biology, Elsevier, 2016. [bib] [abstract]
Lateralization is widespread throughout the animal kingdom and can increase task efficiency via shortening reaction times and saving on neural tissue. However, lateralization might be costly because it increases predictability. In predator-prey interactions, for example, predators might increase capture success because of specialization in a lateralized attack, but at the cost of increased predictability to their prey, constraining the evolution of lateralization. One unexplored mechanism for evading such costs is group hunting: this would allow individual-level specialization, while still allowing for group-level unpredictability. We investigated this mechanism in group hunting sailfish, Istiophorus platypterus, attacking schooling sardines, Sardinella aurita. During these attacks, sailfish alternate in attacking the prey using their elongated bills to slash or tap the prey. This rapid bill movement is either leftward or rightward. Using behavioral observations of identifiable individual sailfish hunting in groups, we provide evidence for individual-level attack lateralization in sailfish. More strongly lateralized individuals had a higher capture success. Further evidence of lateralization comes from morphological analyses of sailfish bills that show strong evidence of one-sided micro-teeth abrasions. Finally, we show that attacks by single sailfish are indeed highly predictable, but predictability rapidly declines with increasing group size because of a lack of population-level lateralization. Our results present a novel benefit of group hunting: by alternating attacks, individual-level attack lateralization can evolve, without the negative consequences of individual-level predictability. More generally, our results suggest that group hunting in predators might provide more suitable conditions for the evolution of strategy diversity compared to solitary life.
[2016] Guppies occupy consistent positions in social networks: mechanisms and consequences (Stefan Krause, Alexander D. M. Wilson, Indar W. Ramnarine, James E. Herbert-Read, Romain J. G. Clément, Jens Krause), In Behavioral Ecology, Oxford University Press, 2016. [bib] [abstract]
The social network approach has focused increasing attention on the complex web of relationships found in animal groups and populations. As such, network analysis has been used frequently to identify the role that particular individuals play in their social interactions and this approach has led to the question of whether, and in what context, individuals consistently occupy certain positions within their network. Here we investigated the social networks of guppies, Poecilia reticulata, in the wild and tested whether 1) individual fish occupy consistent positions in their network and 2) whether these positions are robust to experimental manipulations to their habitat. Our habitat manipulations involved increasing and decreasing the surface area of their pools as well as translocating an entire pool population between different pools in situ. We found that guppies did indeed consistently occupy positions within their social networks, irrespective of the type of manipulation and that individual network positions vary between individuals. Our results suggest that at least 2 factors contribute to the observed individual variation in network position including 1) the tendency to be social and 2) sex-specific social preferences. Finally, we used a simulation to explore the implications of individuals consistently occupying different network positions regarding the exposure of fish to parasites and predators. The time until infection decreased with increasing rank of individual betweenness and the predation risk increased with decreasing rank of the individual node strength thus illustrating the potential ecological and evolutionary consequences of consistent network positions.
[2016] Proto-cooperation: group hunting sailfish improve hunting success by alternating attacks on grouping prey (James E. Herbert-Read, Pawel Romanczuk, Stefan Krause, Daniel Strömbom, Pierre Couillaud, Paolo Domenici, Ralf H. J. M. Kurvers, Stefano Marras, John F. Steffensen, Alexander D. M. Wilson, Jens Krause), In Proceedings of the Royal Society B: Biological Sciences, The Royal Society, 2016. [bib] [abstract]
We present evidence of a novel form of group hunting. Individual sailfish (Istiophorus platypterus) alternate attacks with other group members on their schooling prey (Sardinella aurita). While only 24% of attacks result in prey capture, multiple prey are injured in 95% of attacks, resulting in an increase of injured fish in the school with the number of attacks. How quickly prey are captured is positively correlated with the level of injury of the school, suggesting that hunters can benefit from other conspecifics' attacks on the prey. To explore this, we built a mathematical model capturing the dynamics of the hunt. We show that group hunting provides major efficiency gains (prey caught per unit time) for individuals in groups of up to 70 members. We also demonstrate that a free riding strategy, where some individuals wait until the prey are sufficiently injured before attacking, is only beneficial if the cost of attacking is high, and only then when waiting times are short. Our findings provide evidence that cooperative benefits can be realized through the facilitative effects of individuals’ hunting actions without spatial coordination of attacks. Such 'proto-cooperation' may be the pre-cursor to more complex group-hunting strategies.
[2015] Integrating network analysis, sensor tags, and observation to understand shark ecology and behavior (Alexander D. M. Wilson, Jacob W. Brownscombe, Jens Krause, Stefan Krause, Lee F. G. Gutowsky, Edward J. Brooks, Steven J. Cooke), In Behavioral Ecology, Oxford University Press, 2015. [bib] [abstract]
Group living in animals is a well-studied phenomenon, having been documented extensively in a wide range of terrestrial, freshwater, and marine species. Although social dynamics are complex across space and time, recent technological and analytical advances enable deeper understanding of their nature and ecological implications. While for some taxa, a great deal of information is known regarding the mechanistic underpinnings of these social processes, knowledge of these mechanisms in elasmobranchs is lacking. Here, we used an integrative and novel combination of direct observation, accelerometer biologgers, and recent advances in network analysis to better understand the mechanistic bases of individual-level differences in sociality (leadership, network attributes) and diel patterns of locomotor activity in a widespread marine predator, the lemon shark (Negaprion brevirostris). We found that dynamic models of interaction based on Markov chains can accurately predict juvenile lemon shark social behavior and that lemon sharks did not occupy consistent positions within their network. Lemon sharks did however preferentially associate with specific group members, by sex as well as by similarity or nonsimilarity for a number of behavioral (nonsimilarity: leadership) and locomotor traits (similarity: proportion of time swimming “fast,” mean swim duration; nonsimilarity: proportion of swimming bursts/transitions between activity states). Our study provides some of the first information on the mechanistic bases of group living and personality in sharks and further, a potential experimental approach for studying fine-scale differences in behavior and locomotor patterns in difficult-to-study organisms.
[2015] Social networks in changing environments (Alexander D. M. Wilson, Stefan Krause, Indar W. Ramnarine, Karoline K. Borner, Romain J. G. Clément, Ralf H. J. M. Kurvers, Jens Krause), In Behavioral Ecology and Sociobiology, Springer, 2015. [bib] [abstract]
Social network analysis (SNA) has become a widespread tool for the study of animal social organisation. However despite this broad applicability, SNA is currently limited by both an overly strong focus on pattern analysis as well as a lack of dynamic interaction models. Here, we use a dynamic modelling approach that can capture the responses of social networks to changing environments. Using the guppy, Poecilia reticulata, we identified the general properties of the social dynamics underlying fish social networks and found that they are highly robust to differences in population density and habitat changes. Movement simulations showed that this robustness could buffer changes in transmission processes over a surprisingly large density range. These simulation results suggest that the ability of social systems to self-stabilise could have important implications for the spread of infectious diseases and information. In contrast to habitat manipulations, social manipulations (e.g. change of sex ratios) produced strong, but short-lived, changes in network dynamics. Lastly, we discuss how the evolution of the observed social dynamics might be linked to predator attack strategies. We argue that guppy social networks are an emergent property of social dynamics resulting from predator–prey co-evolution. Our study highlights the need to develop dynamic models of social networks in connection with an evolutionary framework.
[2015] Turbidity affects social dynamics in Trinidadian guppies (Karoline K. Borner, Stefan Krause, Thomas Mehner, Silva Uusi-Heikkilä, Indar W. Ramnarine, Jens Krause), In Behavioral Ecology and Sociobiology, Springer, 2015. [bib] [abstract]
Turbidity, caused by suspended particles in the water column, induces light scattering and shifts in the wavelengths of light. These changes may impair the ability of fish to use physical cues and hence may modify social interactions. We experimentally investigated the social interactions of guppies, Poecilia reticulata, in clear and turbid water. Fish were significantly less active, formed smaller shoals and were found to be more often alone in turbid than in clear water. A Markov chain analysis revealed significant differences in the social dynamics when comparing clear and turbid water conditions. The probability of leaving a particular nearest neighbour and the probability of choosing some neighbour after swimming around alone differed between the treatments. Our results indicate that turbidity has a number of different effects on the social interactions of the guppy, and we discuss their potential costs and benefits and wider implications.
[2014] Seasonal Patterns of Mixed Species Groups in Large East African Mammals (Christian Kiffner, John Kioko, Cecilia Leweri, Stefan Krause), In PLoS ONE, volume 9, 2014. [bib] [pdf] [abstract]
Mixed mammal species groups are common in East African savannah ecosystems. Yet, it is largely unknown if co-occurrences of large mammals result from random processes or social preferences and if interspecific associations are consistent across ecosystems and seasons. Because species may exchange important information and services, understanding patterns and drivers of heterospecific interactions is crucial for advancing animal and community ecology. We recorded 5403 single and multi-species clusters in the Serengeti-Ngorongoro and Tarangire-Manyara ecosystems during dry and wet seasons and used social network analyses to detect patterns of species associations. We found statistically significant associations between multiple species and association patterns differed spatially and seasonally. Consistently, wildebeest and zebras preferred being associated with other species, whereas carnivores, African elephants, Maasai giraffes and Kirk's dik-diks avoided being in mixed groups. During the dry season, we found that the betweenness (a measure of importance in the flow of information or disease) of species did not differ from a random expectation based on species abundance. In contrast, in the wet season, we found that these patterns were not simply explained by variations in abundances, suggesting that heterospecific associations were actively formed. These seasonal differences in observed patterns suggest that interspecific associations may be driven by resource overlap when resources are limited and by resource partitioning or anti-predator advantages when resources are abundant. We discuss potential mechanisms that could drive seasonal variation in the cost-benefit tradeoffs that underpin the formation of mixed-species groups.
[2014] How sailfish use their bills to capture schooling prey (Paolo Domenici, Alexander D. M. Wilson, Ralf H. J. M. Kurvers, Stefano Marras, James E. Herbert-Read, John F. Steffensen, Stefan Krause, Paul E. Viblanc, Pierre Couillaud, Jens Krause), In Proceedings of the Royal Society B: Biological Sciences, The Royal Society, 2014. [bib] [pdf] [abstract]
The istiophorid family of billfishes is characterized by an extended rostrum or 'bill'. While various functions (e.g. foraging and hydrodynamic benefits) have been proposed for this structure, until now no study has directly investigated the mechanisms by which billfishes use their rostrum to feed on prey. Here, we present the first unequivocal evidence of how the bill is used by Atlantic sailfish (Istiophorus albicans) to attack schooling sardines in the open ocean. Using high-speed video-analysis, we show that (i) sailfish manage to insert their bill into sardine schools without eliciting an evasive response and (ii) subsequently use their bill to either tap on individual prey targets or to slash through the school with powerful lateral motions characterized by one of the highest accelerations ever recorded in an aquatic vertebrate. Our results demonstrate that the combination of stealth and rapid motion make the sailfish bill an extremely effective feeding adaptation for capturing schooling prey.
[2014] Dynamic social networks in guppies (Poecilia reticulata) (Alexander D. M. Wilson, Stefan Krause, Richard James, Darren P. Croft, Indar W. Ramnarine, Karoline K. Borner, Romain J. G. Clément, Jens Krause), In Behavioral Ecology and Sociobiology, Springer, 2014. [bib] [abstract]
One of the main challenges in the study of social networks in vertebrates is to close the gap between group patterns and dynamics. Usually scan samples or transect data are recorded to provide information about social patterns of animals, but these techniques themselves do not shed much light on the underlying dynamics of such groups. Here we show an approach which captures the fission-fusion dynamics of a fish population in the wild and demonstrates how the gap between pattern and dynamics may be closed. Our analysis revealed that guppies have complex association patterns that are characterised by close strong connections between individuals of similar behavioural type. Intriguingly, the preference for particular social partners is not expressed in the length of associations but in their frequency. Finally, we show that the observed association preferences could have important consequences for transmission processes in animal social networks, thus moving the emphasis of network research from descriptive mechanistic studies to functional and predictive ones.
[2013] Accurate decisions in an uncertain world: collective cognition increases true positives while decreasing false positives (Max Wolf, Ralf H. J. M. Kurvers, Ashley J. W. Ward, Stefan Krause, Jens Krause), In Proceedings of the Royal Society B: Biological Sciences, The Royal Society, volume 280, 2013. [bib] [pdf] [abstract]
In a wide range of contexts, including predator avoidance, medical decision-making and security screening, decision accuracy is fundamentally constrained by the trade-off between true and false positives. Increased true positives are possible only at the cost of increased false positives; conversely, decreased false positives are associated with decreased true positives. We use an integrated theoretical and experimental approach to show that a group of decision-makers can overcome this basic limitation. Using a mathematical model, we show that a simple quorum decision rule enables individuals in groups to simultaneously increase true positives and decrease false positives. The results from a predator-detection experiment that we performed with humans are in line with these predictions: (i) after observing the choices of the other group members, individuals both increase true positives and decrease false positives, (ii) this effect gets stronger as group size increases, (iii) individuals use a quorum threshold set between the average true- and false-positive rates of the other group members, and (iv) individuals adjust their quorum adaptively to the performance of the group. Our results have broad implications for our understanding of the ecology and evolution of group-living animals and lend themselves for applications in the human domain such as the design of improved screening methods in medical, forensic, security and business applications.
[2013] Network position: a key component in the characterization of social personality types (Alexander D. M. Wilson, Stefan Krause, Niels J. Dingemanse, Jens Krause), In Behavioral Ecology and Sociobiology, Springer, volume 67, 2013. [bib] [abstract]
In recent years, animal social interactions have received much attention in terms of personality research (e.g. aggressive or cooperative interactions). However, other components of social behaviour such as those describing the intensity, frequency, directedness and individual repeatability of interactions in animal groups have largely been neglected. Network analysis offers a valuable opportunity to characterize individual consistency of traits in labile social groups and therein provide novel insights to personality research in ways previously not possible using traditional techniques. Should individual network positions be consistently different between individuals under changing conditions, they might reflect expressions of an individual's personality. Here, we discuss a conceptual framework for using network analyses to infer the presence of individual differences and present a statistical test based on randomization techniques for testing the consistency of network positions in individuals. The statistical tools presented are useful because if particular individuals consistently occupy key positions in social networks, then this is also likely to have consequences for their fitness as well as for that of others in the population. These consequences may be particularly significant since individual network position has been shown to be important for the transmission of diseases, socially learnt information and genetic material between individuals and populations.
[2013] Reality mining of animal social systems (Jens Krause, Stefan Krause, Robert Arlinghaus, Ioannis Psorakis, Stephen Roberts, Christian Rutz), In Trends in Ecology & Evolution, Elsevier, volume 28, 2013. [bib] [abstract]
The increasing miniaturisation of animal-tracking technology has made it possible to gather exceptionally detailed machine-sensed data on the social dynamics of almost entire populations of individuals, in both terrestrial and aquatic study systems. Here, we review important issues concerning the collection of such data, and their processing and analysis, to identify the most promising approaches in the emerging field of 'reality mining'. Automated technologies can provide data sensing at time intervals small enough to close the gap between social patterns and their underlying processes, providing insights into how social structures arise and change dynamically over different timescales. Especially in conjunction with experimental manipulations, reality mining promises significant advances in basic and applied research on animal social systems.
[2013] Collective Cognition in Humans: Groups Outperform Their Best Members in a Sentence Reconstruction Task (Romain J. G. Clément, Stefan Krause, Nikolaus von Engelhardt, Jolyon J. Faria, Jens Krause, Ralf H. J. M. Kurvers), In PLoS ONE, volume 8, 2013. [bib] [pdf] [abstract]
Group-living is widespread among animals and one of the major advantages of group-living is the ability of groups to solve cognitive problems that exceed individual ability. Humans also make use of collective cognition and have simultaneously developed a highly complex language to exchange information. Here we investigated collective cognition of human groups regarding language use in a realistic situation. Individuals listened to a public announcement and had to reconstruct the sentence alone or in groups. This situation is often encountered by humans, for instance at train stations or airports. Using recent developments in machine speech recognition, we analysed how well individuals and groups reconstructed the sentences from a syntactic (i.e., the number of errors) and semantic (i.e., the quality of the retrieved information) perspective. We show that groups perform better both on a syntactic and semantic level than even their best members. Groups made fewer errors and were able to retrieve more information when reconstructing the sentences, outcompeting even their best group members. Our study takes collective cognition studies to the more complex level of language use in humans.
[2013] The role of individuality in collective group movement (James E. Herbert-Read, Stefan Krause, Lesley J. Morrell, Timothy M. Schaerf, Jens Krause, Ashley J. W. Ward), In Proceedings of the Royal Society B: Biological Sciences, The Royal Society, volume 280, 2013. [bib] [pdf] [abstract]
How different levels of biological organization interact to shape each other's function is a central question in biology. One particularly important topic in this context is how individuals' variation in behaviour shapes group-level characteristics. We investigated how fish that express different locomotory behaviour in an asocial context move collectively when in groups. First, we established that individual fish have characteristic, repeatable locomotion behaviours (i.e. median speeds, variance in speeds and median turning speeds) when tested on their own. When tested in groups of two, four or eight fish, we found individuals partly maintained their asocial median speed and median turning speed preferences, while their variance in speed preference was lost. The strength of this individuality decreased as group size increased, with individuals conforming to the speed of the group, while also decreasing the variability in their own speed. Further, individuals adopted movement characteristics that were dependent on what group size they were in. This study therefore shows the influence of social context on individual behaviour. If the results found here can be generalized across species and contexts, then although individuality is not entirely lost in groups, social conformity and group-size-dependent effects drive how individuals will adjust their behaviour in groups.
[2012] Verborgenes Rechencluster im neuen Studienarbeitsraum der Elektrotechnik und Informatik (Torsten Teubler, Stefan Krause, Horst Hellbrück), In Impulse, volume 16, 2012. [bib] [pdf]
[2011] Swarm intelligence in humans: diversity can trump ability (Stefan Krause, Richard James, Jolyon J. Faria, Graeme D. Ruxton, Jens Krause), In Animal Behaviour, Elsevier, volume 81, 2011. [bib] [abstract]
We identify some of the possibilities and limitations of human swarm intelligence (SI) using the response of the public to two types of cognitive problems. Furthermore, we propose a simple measure for the quantification of collective information that could form the basis for SI in study populations for specific tasks. Our three main results are (1) that the potential benefits of SI depend on the type of problem, (2) that individual performance and collective performance can be uncorrelated and that a group of individually high performers can be outcompeted by a same-size group of individually low performers, and (3) that adding diversity to a group can be more beneficial than adding expertise. Our results question the emphasis that societies and organizations can put on individual performance to the detriment of diversity as far as teams are concerned. Nevertheless, it is important to point out that while diversity is a necessary condition for effective SI, diversity alone is clearly not sufficient. Finally, we discuss the potential implications of our findings for the evolution of group composition and the maintenance of personality diversity in animals.
[2011] Kollektives Verhalten und Schwarmintelligenz (Jens Krause, Stefan Krause), In Darwin meets Business, Gabler/Springer, 2011. [bib]
[2011] Assortative interactions and leadership in a free-ranging population of juvenile lemon shark Negaprion brevirostris (Tristan L. Guttridge, Samuel H. Gruber, Joseph D. DiBattista, Kevin A. Feldheim, Darren P. Croft, Stefan Krause, Jens Krause), In Marine Ecology Progress Series, volume 423, 2011. [bib] [abstract]
For marine predators there is a paucity of studies on social behaviour, and even fewer studies have quantified interactions between individuals. In the present study, we looked at the social structure and leadership of free-ranging juvenile lemon shark Negaprion brevirostris in a known aggregation site, Bimini, the Bahamas. Observations of these sharks were made from towers placed in a mangrove inlet, where clear, shallow, protected waters made it possible to record group compositions of externally colour-code tagged wild juvenile lemon sharks. Thirty-eight different individual sharks were observed to use the area over a 2 yr period. Results show repeated social interactions suggestive of active partner preference. In addition, we found that group structure was mostly explained by body length, and possibly by preference for relatives but not by sex. Finally, we observed that some sharks led more groups than others and that those lead individuals were usually larger than those following them. This study quantifies the social structure of a free-ranging shark population and provides novel insights into the social behaviour of juvenile sharks.
[2011] Associations between the drill (Mandrillus leucophaeus) and sympatric monkeys in Korup National Park, Cameroon (Christos Astaras, Stefan Krause, Lutz Mattner, Christoph Rehse, Matthias Waltert), In American Journal of Primatology, Wiley, volume 73, 2011. [bib] [abstract]
Studies of polyspecific associations among African forest primates have primarily focused on arboreal Cercopithecus and Procolobus/Colobus species. We examined the association frequency of the terrestrial drill (Mandrillus leucophaeus) with six sympatric monkey species in Korup National Park, Cameroon, testing reports that Mandrillus associations are infrequent and transient. We conducted 3,284km of trail walks for 12 months (February-June 2006; July 2007 to January 2008), recording species composition in 612 primate clusters. Using a Markov chain Monte Carlo test, we compared the observed frequency of dyadic associations against null models of "no association". A novel conservative statistical approach which addresses possible dependence of observations close in time was also used, further strengthening confidence in our findings. Drills associated with all monkeys throughout the study period, and were with at least one other species (range 1-5) in half of the encounters. The association frequency of drills with red-capped mangabeys (Cercocebus torquatus) was greater than expected by chance, which is interesting given the morphological adaptation of the Mandrillus-Cercocebus clade for the exploitation of the same dietary niche, hard seeds. The difference we observed in the use of forest strata by drills and mangabeys may reflect a strategy to reduce food competition while in association. The nature and duration of observed drill associations varied. Although some associations seemed to be chance encounters, others lasted for hours with the involved species foraging together.
[2010] Swarm intelligence in animals and humans (Jens Krause, Graeme D. Ruxton, Stefan Krause), In Trends in Ecology & Evolution, Elsevier, volume 25, 2010. [bib] [abstract]
Electronic media have unlocked a hitherto largely untapped potential for swarm intelligence (SI; generally, the realisation that group living can facilitate solving cognitive problems that go beyond the capacity of single animals) in humans with relevance for areas such as company management, prediction of elections, product development and the entertainment industry. SI is a rapidly developing topic that has become a hotbed for both innovative research and wild speculation. Here, we tie together approaches from seemingly disparate areas by means of a general definition of SI to unite SI work on both animal and human groups. Furthermore, we identify criteria that are important for SI to operate and propose areas in which further progress with SI research can be made.
[2010] Collective behavior in road crossing pedestrians: the role of social information (Jolyon J. Faria, Stefan Krause, Jens Krause), In Behavioral Ecology, Oxford University Press, volume 21, 2010. [bib] [pdf] [abstract]
Social information use is common in a wide range of group-living animals, notably in humans. We investigated social information use by pedestrians in a potentially dangerous scenario: at a road crossing. To judge a safe gap in traffic, pedestrians can use social information, such as the crossing behavior of others, and follow others across the road. We tested if pedestrians followed others in this scenario by analyzing pedestrian starting position and crossing order. First, we found that neighbors of a crossing pedestrian tended to cross before other waiting pedestrians and that this tendency was significantly higher in observed pedestrians than in a null model: a simulation in which pedestrians did not follow each other. Also, by fitting the null model, we found that on average a person was 1.5-2.5 times more likely to cross if their neighbor had started to cross. Second, we found that males tended to follow others more than females. Third, we observed that some individuals started to cross and then returned to the roadside. These individuals were more frequently found in groups and tended to start to cross relatively later than other pedestrians. These observations suggest that some of these individuals made incorrect decisions about the timing of their crossing and that this was due to social information use. Finally, we propose that the relatively small benefit of a reduced waiting time came at the cost of an increased risk of injury, making the beneficial value of social information use questionable in this context.
[2009] Social network analysis and valid Markov chain Monte Carlo tests of null models (Stefan Krause, Lutz Mattner, Richard James, Tristan Guttridge, Mark J. Corcoran, Samuel H. Gruber, Jens Krause), In Behavioral Ecology and Sociobiology, Springer, volume 63, 2009. [bib] [abstract]
Analyses of animal social networks derived from group-based associations often rely on randomisation methods developed in ecology (Manly, Ecology 76:1109-1115, 1995) and made available to the animal behaviour community through implementation of a pair-wise swapping algorithm by Bejder et al. (Anim Behav 56:719-725, 1998). We report a correctable flaw in this method and point the reader to a wider literature on the subject of null models in the ecology literature. We illustrate the importance of correcting the method using a toy network and use it to make a preliminary analysis of a network of associations among eagle rays.
[2000] Leadership in fish shoals (Jens Krause, Daniel Hoare, Stefan Krause, Charlotte K. Hemelrijk, Daniel I. Rubenstein), In Fish and fisheries, Blackwell, volume 1, 2000. [bib] [abstract]
Leadership is not an inherent quality of animal groups that show directional locomotion. However, there are other factors that may be responsible for the occurrence of leadership in fish shoals, such as individual differences in nutritional state between group members. It appears that front fish have a strong influence on directional shoal movements and that individuals that occupy such positions are often characterised by larger body lengths and lower nutritional state. Potential interactions between the two factors and their importance for positioning within shoals need further attention. Initiation of directional movement in stationary shoals and position preferences in mobile shoals need to be addressed separately because they are potentially subject to different constraints. Individuals that initiate a swimming direction may not necessarily be capable of the sustained high swimming performance required to keep the front position or have the motivation to do so, for that matter. More empirical and theoretical work is necessary to look at the factors controlling positioning behaviour within shoals, as well as overall shoal shape and structure. Tracking of marked individuals whose positioning behaviour is monitored over extended time periods of hours or days would be useful. There is an indication that shoal positions are rotated by individuals according to their nutritional needs, with hungry fish occupying front positions only for as long as necessary to regain their nutritional balance. This suggests that shoal members effectively take turns at being leaders. There is a need for three-dimensional recordings of shoaling behaviour using high-speed video systems that allow a detailed analysis of information transfer in shoals of different size. The relationship between leadership and shoal size might provide an interesting field for future research. Most studies to date have been restricted to shoals of small and medium size and more information on larger shoals would be useful.
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R script implementing the test described in Wilson et al. (2013) Network position: a key component in the characterization of social personality types. The zip file also contains a short description of how to use the script.