The Experts below are selected from a list of 8610 Experts worldwide ranked by ideXlab platform

Charlotte K. Hemelrijk - One of the best experts on this subject based on the ideXlab platform.

  • domino like propagation of collective u turns in Fish Schools
    bioRxiv, 2017
    Co-Authors: Valentin Lecheval, Charlotte K. Hemelrijk, Clément Sire, Li Jiang, Pierre Tichit, Guy Theraulaz
    Abstract:

    Moving animal groups such as Schools of Fish or flocks of birds often undergo sudden collective changes of their travelling direction as a consequence of stochastic fluctuations in heading of the individuals. However, the mechanisms by which these behavioural fluctuations arise at the individual level and propagate within a group are still unclear. In the present study, we combine an experimental and theoretical approach to investigate spontaneous collective U-turns in groups of rummy-nose tetra (Hemigrammus rhodostomus) swimming in a ring-shaped tank. U-turns imply that Fish switch their heading between the clockwise and anticlockwise direction. We reconstruct trajectories of individuals moving alone and in groups of different sizes. We show that the group decreases its swimming speed before a collective U-turn. This is in agreement with previous theoretical predictions showing that speed decrease leads to an amplification of fluctuations in heading in the group, which can trigger U-turns. These collective U-turns are mostly initiated by individuals at the front of the group. Once an individual has initiated a U-turn, the new direction propagates through the group from front to back without amplification or dampening, resembling the dynamics of falling dominoes. The mean time between collective U-turns sharply increases as the size of the group increases. We develop an Ising spin model integrating anisotropic and asymmetrical interactions between Fish and their tendency to follow the majority of their neighbours nonlinearly (social conformity). The model quantitatively reproduces key features of the dynamics and the magnitude of collective U-turns observed in experiments.

  • Schools of Fish and flocks of birds their shape and internal structure by self organization
    Interface Focus, 2012
    Co-Authors: Charlotte K. Hemelrijk, Hanno Hildenbrandt
    Abstract:

    Models of self-organization have proved useful in revealing what processes may underlie characteristics of swarms. In this study, we review model-based explanations for aspects of the shape and internal structure of groups of Fish and of birds travelling undisturbed (without predator threat). Our models attribute specific collective traits to locomotory properties. Fish slow down to avoid collisions and swim at a constant depth, whereas birds fly at low variability of speed and lose altitude during turning. In both the models of Fish and birds, the ‘bearing angle’ to the nearest neighbour emerges as a side-effect of the ‘blind angle’ behind individuals and when group size becomes larger, temporary subgroups may increase the complexity of group shape and internal structure. We discuss evidence for model-based predictions and provide a list of new predictions to be tested empirically.

  • Simulations of the social organization of large Schools of Fish whose perception is obstructed
    Applied Animal Behaviour Science, 2012
    Co-Authors: Hanspeter Kunz, Charlotte K. Hemelrijk
    Abstract:

    a b s t r a c t Individual-based models have shown that simple interactions among moving individu- als (repulsion, attraction and alignment) result in travelling Schools that resemble those of real Fish. In most models individuals interact with all neighbours within sensory range which usually includes almost all the individuals of the school. Thus, it implies (almost) global perception. However, in reality in large groups, individuals will only interact with their neighbours close by, because they cannot perceive those farther away, since they are masked by closer ones. Here, we have developed a new model to investigate how such obstruction of perception influences aspects of social organization in Schools of up to 10,000 individuals. We will show that in small Schools of up to approximately 30 individuals group shape and density resembles that obtained with global perception, because in small Schools hardly anyone is masked by others: school shape is oblong and the density is highest in the frontal half of the school. With increasing group size, from approximately 200 individuals onwards, internal density becomes variable over time, regions of high and low density develop at any location within a school, and group shape becomes more complex, in the sense that inward bounds and appendages occur more frequently. The complexity of shape and internal structure arises because, due to their limited perception, individuals interact relatively more locally in larger Schools. In case of global perception, however, shape remains elliptical for all group sizes and in groups above 1000 individuals, the Schools become unrealistically dense. In sum, our results show that obstructed perception in itself suffices to generate a realistic organi- zation of large Schools and that no extra rules for 'coping' with many individuals are needed.

  • Simulations of the social organization of large Schools of Fish whose perception is obstructed
    Applied Animal Behaviour Science, 2012
    Co-Authors: Hanspeter Kunz, Charlotte K. Hemelrijk
    Abstract:

    Individual-based models have shown that simple interactions among moving individuals (repulsion, attraction and alignment) result in travelling Schools that resemble those of real Fish. In most models individuals interact with all neighbours within sensory range which usually includes almost all the individuals of the school. Thus, it implies (almost) global perception. However, in reality in large groups, individuals will only interact with their neighbours close by, because they cannot perceive those farther away, since they are masked by closer ones. Here, we have developed a new model to investigate how such obstruction of perception influences aspects of social organization in Schools of up to 10,000 individuals. We will show that in small Schools of up to approximately 30 individuals group shape and density resembles that obtained with global perception, because in small Schools hardly anyone is masked by others: school shape is oblong and the density is highest in the frontal half of the school. With increasing group size, from approximately 200 individuals onwards, internal density becomes variable over time, regions of high and low density develop at any location within a school, and group shape becomes more complex, in the sense that inward bounds and appendages occur more frequently. The complexity of shape and internal structure arises because, due to their limited perception, individuals interact relatively more locally in larger Schools. In case of global perception, however, shape remains elliptical for all group sizes and in groups above 1000 individuals, the Schools become unrealistically dense. In sum, our results show that obstructed perception in itself suffices to generate a realistic organization of large Schools and that no extra rules for 'coping' with many individuals are needed. (C) 2012 Elsevier B.V. All rights reserved

  • Emergence of Oblong School Shape: Models and Empirical Data of Fish
    Ethology, 2010
    Co-Authors: Charlotte K. Hemelrijk, Hanno Hildenbrandt, Jose Reinders, Eize Stamhuis
    Abstract:

    The main benefit of the oblong shape of Schools of Fish is supposed to be the protection against predation. Models of self-organised travelling groups have shown that this shape may arise as a side effect of the avoidance of collisions with group members. These models were developed for Schools of Fish in open water, whereas the oblong shape of Schools of real Fish has mostly been observed in Schools in tanks. Therefore, it is not known how school shape in a tank originates neither in models nor in real Fish. To find out what causes this shape, we use the combination of a theoretical and an empirical study. We test the predictions produced by our earlier models regarding the effect of school size on the school shape both in a model of self-organised schooling in a tank and empirically. Empirically, we study the 3D positions of all individuals in the Schools of 10‐60 real mullets (Chelon labrosus). We calculate for each individual its distance to its nearest neighbour and its velocity and we measure per school its length and width. The relation between school shape and size in the model and in the real mullets supports our prediction and thus supports the hypothesis that school shape may be emergent from the avoidance of collisions during coordinated travelling.

Ashley J. W. Ward - One of the best experts on this subject based on the ideXlab platform.

Hanno Hildenbrandt - One of the best experts on this subject based on the ideXlab platform.

  • Schools of Fish and flocks of birds their shape and internal structure by self organization
    Interface Focus, 2012
    Co-Authors: Charlotte K. Hemelrijk, Hanno Hildenbrandt
    Abstract:

    Models of self-organization have proved useful in revealing what processes may underlie characteristics of swarms. In this study, we review model-based explanations for aspects of the shape and internal structure of groups of Fish and of birds travelling undisturbed (without predator threat). Our models attribute specific collective traits to locomotory properties. Fish slow down to avoid collisions and swim at a constant depth, whereas birds fly at low variability of speed and lose altitude during turning. In both the models of Fish and birds, the ‘bearing angle’ to the nearest neighbour emerges as a side-effect of the ‘blind angle’ behind individuals and when group size becomes larger, temporary subgroups may increase the complexity of group shape and internal structure. We discuss evidence for model-based predictions and provide a list of new predictions to be tested empirically.

  • Emergence of Oblong School Shape: Models and Empirical Data of Fish
    Ethology, 2010
    Co-Authors: Charlotte K. Hemelrijk, Hanno Hildenbrandt, Jose Reinders, Eize Stamhuis
    Abstract:

    The main benefit of the oblong shape of Schools of Fish is supposed to be the protection against predation. Models of self-organised travelling groups have shown that this shape may arise as a side effect of the avoidance of collisions with group members. These models were developed for Schools of Fish in open water, whereas the oblong shape of Schools of real Fish has mostly been observed in Schools in tanks. Therefore, it is not known how school shape in a tank originates neither in models nor in real Fish. To find out what causes this shape, we use the combination of a theoretical and an empirical study. We test the predictions produced by our earlier models regarding the effect of school size on the school shape both in a model of self-organised schooling in a tank and empirically. Empirically, we study the 3D positions of all individuals in the Schools of 10‐60 real mullets (Chelon labrosus). We calculate for each individual its distance to its nearest neighbour and its velocity and we measure per school its length and width. The relation between school shape and size in the model and in the real mullets supports our prediction and thus supports the hypothesis that school shape may be emergent from the avoidance of collisions during coordinated travelling.

  • self organized shape and frontal density of Fish Schools
    Ethology, 2008
    Co-Authors: Charlotte K. Hemelrijk, Hanno Hildenbrandt
    Abstract:

    Models of swarming (based on avoidance, alignment and attraction) produce patterns of behaviour also seen in Schools of Fish. However, the significance of such similarities has been questioned, because some model assumptions are unrealistic [e.g. speed in most models is constant with random error, the perception is global and the size of the Schools that have been studied is small (up to 128 individuals)]. This criticism also applies to our former model, in which we demonstrated the emergence of two patterns of spatial organization, i.e. oblong school form and high frontal density, which are supposed to function as protection against predators. In our new model we respond to this criticism by making the following improvements: individuals have a preferred ‘cruise speed’ from which they can deviate in order to avoid others or to catch up with them. Their range of perception is inversely related to density, with which we take into account that high density limits the perception of others that are further away. Swarm sizes range from 10 to 2000 individuals. The model is three-dimensional. Further, we show that the two spatial patterns (oblong shape and high frontal density) emerge by self-organization as a side-effect of coordination at two speeds (of two or four body lengths per second) for Schools of sizes above 20. Our analysis of the model leads to the development of a new set of hypotheses. If empirical data confirm these hypotheses, then in a school of real Fish these patterns may arise as a side-effect of their coordination in the same way as in the model.

Maud I. A. Kent - One of the best experts on this subject based on the ideXlab platform.

Satoshi Hirata - One of the best experts on this subject based on the ideXlab platform.

  • Spatial positioning of individuals in a group of feral horses: a case study using drone technology
    Mammal Research, 2019
    Co-Authors: Sota Inoue, Renata S. Mendonça, Shinya Yamamoto, Monamie Ringhofer, Carlos Pereira, Satoshi Hirata
    Abstract:

    Spatial positioning of individuals in animal groups has been studied from numerous perspectives. However, although many studies have focused on spatial position in flocks of birds and Schools of Fish, relatively few studies have been conducted in mammals with high accuracy. Because some mammal species form societies, we wondered how social relationships among mammals within a group influence each individual’s spatial position. To address this issue, we used drones to obtain accurate positioning of individuals in a feral horse group on the Serra D’ Arga mountain in Portugal. The results of our study revealed the following characteristics: (1) the male in between social and spatial relationships indicated that they are independent from each other. The present study is the first to reveal the characteristics of spatial positioning in a mammalian group using drone technology. The harem group was located in the periphery; (2) as in other species, individuals had areas of repulsion and attraction, and (3) nearest neighbors were located more toward the sides than to the back or front. We also measured the social relationships between individuals in terms of grooming frequency. Social network analyses of the correlation between social and spatial relationships indicated that they are independent from each other. The present study is the first to reveal the characteristics of spatial positioning in a mammalian group using drone technology.