Studying the collective behavior of fishes often requires tracking a great number of individuals. When many fishes move together, it is common for individuals to move so close to each other that some fishes superimpose themselves on others during one or several units of time, which impacts on tracking accuracy (i.e., loss of fish trajectories, interchange of fish identities). Type 1 occlusions arise when two fishes swim so near each other that they look like one long fish, whereas type 2 occlusions occur when the fishes' trajectories cross to create a T- or X-shaped individual. We propose an image processing method for resolving these types of occlusions when multitracking shoals in two dimensions. We assessed processing effectiveness after videorecording shoals of 20 and 40 individuals of two species that exhibit different shoal styles: zebrafish (Danio rerio) and black neon tetras (Hyphessobrycon herbertaxelrodi). Results show that, although the number of occlusions depended on both the number of individuals and the species, the method is able to effectively resolve a great deal of occlusions, irrespective of the species and the number of individuals. It also produces images that can be used in a multitracking system to detect individual fish trajectories. Compared to other methods, our approach makes it possible to study shoals with water depths similar to those seen in the natural conditions of the two species studied.

We empirically applied the GrooFiWorld agent-based model (Puga-González et al. 2009) in a group of captive redcapped mangabeys (Cercocebus torquatus). We analysed several measurements related to aggression and affiliative patterns. The group adopted a combination of despotic and egalitarian behaviours resulting from the behavioural flexibility observed in the Cercopithecinae subfamily. Our study also demonstrates that the GrooFiWorld agent-based model can be extended to other members of the Cercopithecinae subfamily generating parsimonious hypotheses related to the social organization.[Dolado R and Beltran FS 2012 Emergent patterns of social organization in captive Cercocebus torquatus: Testing the GrooFiWorld agent-based model.

Fish can gain significant adaptive advantages when living in a group and they exhibit a wide variety of types of collective motion. The scientific literature recognizes 2 main patterns: shoals (aggregations of individuals that remain close to each other), and schools (aggregations of aligned, or polarized, individuals). We analyzed the collective motion of 2 social fish species, zebrafish (Danio rerio) and black neon tetra (Hyphessobrycon herbertaxelrodi), and compared their patterns of movement and the effect of group size and environmental constraints such as water column height and tank geometry on the collective motion of both species. We recorded the movement of groups of fish (n = 10 and n = 20) using 2 tank geometries: a rectangular shape and a rectangular shape with rounded corners; and we also manipulated the water column height (15 and 25 cm). We extracted the individual fish trajectories and calculated indices of cohesion, coordination, group density and group shape. The results showed that the 2 species had different types of collective motion: the zebrafish's global motion matched that of a shoal, while the black neon tetra's motion matched that of a school. Indirect evidence indicated that the 2 species tended to occupy the vertical space differently while swimming in a group. Finally, we found that tank geometry did not affect group polarization, whereas group size had an effect on black neon tetra density, which was higher in small group sizes than in large ones. (PsycINFO Database Record

We have studied how leaders emerge in a group as a consequence of interactions among its members. We propose that leaders can emerge as a consequence of a self-organized process based on local rules of dyadic interactions among individuals. Flocks are an example of self-organized behaviour in a group and properties similar to those observed in flocks might also explain some of the dynamics and organization of human groups. We developed an agent-based model that generated flocks in a virtual world and implemented it in a multi-agent simulation computer program that computed indices at each time step of the simulation to quantify the degree to which a group moved in a coordinated way (index of flocking behaviour) and the degree to which specific individuals led the group (index of hierarchical leadership). We ran several series of simulations in order to test our model and determine how these indices behaved under specific agent and world conditions. We identified the agent, world property, and model parameters that made stable, compact flocks emerge, and explored possible environmental properties that predicted the probability of becoming a leader.

We explored the local motion rules used by interacting individuals in small groups of black neon tetra (Hyphessobrycon herbertaxelrodi) and zebrafish (Danio rerio) to ascertain if and how these rules underlie the fishes' global collective coordinated motion. As these 2 species show very different styles of collective motion in terms of cohesion and polarization, we expected to find differences in their individual behavioral rules. We recorded groups of 2, 3, 4, and 8 fish of each species; tracked their individual trajectories; and studied how their individual turning angles and accelerations varied as a function of heading differences, distances, and relative angles to their neighbors. We found that black neon tetra and zebrafish differed in terms of their preferential positions with respect to their neighbors, the magnitude of turning angles and accelerations, and the way these angles and accelerations are modulated by both the distance from neighbors (thus suggesting a "repulsion" zone in black neon tetra but not in zebrafish) and the heading difference and relative angle to neighbors. Our results enable us to infer that, in black neon tetra, avoiding excessive proximity and collision takes priority over cohesion, and cohesion takes priority over polarization. This provides evidence that rules are similar in species of very different genera and that differences are a matter of degree. Our results also provide substantial empirical evidence to support the theoretical assumptions made in agent-based models that simulate coordinated collective motion in many different animal species.

We empirically tested Hemelrijk's agent-based model (Hemelrijk, 1998), in which dyadic agonistic interaction between primate-group subjects determines their spatial distribution and whether or not the dominant subject has a central position with respect to the other subjects. We studied a group of captive red-capped mangabeys (Cercocebus torquatus torquatus) that met the optimal conditions for testing this model (e.g., a linear dominance hierarchy). We analyzed the spatial distribution of the subjects in relation to their rank in the dominance hierarchy and the results confirmed the validity of this model. In accordance with Hemelrijk's model (Hemelrijk, 1998), the group studied showed an ambiguity-reducing strategy that led to non-central spatial positioning on the part of the dominant subject, thus confirming the model indirectly.Nevertheless, for the model to be confirmed directly, the group has to adopt a risksensitive strategy so that observers can study whether dominant subjects develop spatial centrality. Our study also demonstrated that agent-based models are a good tool for the study of certain complex behaviors observed in primates because these explanatory models can help formulate suggestive hypotheses for exploring new lines of research in primatology.

For group-living primates, social organization hinges upon multiple factors, including group size, group cohesion, and the group's age and sex composition. Fission-fusion dynamics reduce the risks of living in a large group, which can include feeding competition related to the seasonality of resources. Here we report on the group dynamics (i.e. formation of parties) of a population of red-capped mangabeys (Cercocebus torquatus) located in Sentier Nature forest, South Loango National Park, Gabon, and examine the role of fruit availability in episodes of fission-fusion and shifting range use during the peak fruiting season of 2014. To assess fission-fusion dynamics, we obtained data on party type (i.e. number, size and age-sex composition), the effect of availability of fruit from 4 tree species on the home range and habitat used by parties, and the periodicity of these processes. The results show that red-capped mangabeys displayed seasonal fission-fusion dynamics related to fruit availability during the season under study.

Miller and Gerlai proposed two methods for determining shoal membership in zebrafish (Danio rerio), based on momentary mean inter-individual distances and on post-hoc analysis of trajectories of nearest neighbor distances, respectively. We propose an alternative method based on momentary nearest neighbor distances and compare the three methods using simulation. In general, our method yields results more similar to Miller and Gerlai's second than first methods, but is computationally simpler.3 Keywords Shoal membership, inter-individual distances, nearest neighbor distances, agent-based simulation. 4 Coordinated collective motion is a common phenomenon in numerous animal species, consisting of many individuals adjusting their movements to achieve coherent group travel. Coordinated motion exists when: (a) the group is polarized or aligned, i.e., most individuals move with a similar heading, and change heading in a synchronized way; (b) most individuals adjust their speed to the average group speed; and (c) individuals tend to aggregate, while keeping some distance from their neighbors to avoid collision.Bird flocks and fish schools are two prominent instances of coordinated collective motion, whose functionality, evolution and underlying organizational mechanisms have been the subject of many studies in recent decades (e.g., [1,2,3,4]).Two kinds of group organization are usually described in fish: shoals and schools. According to Pitcher and Parrish [5], "groups of fish that remain together for social reasons are here termed shoals (…) synchronized and polarized swimming groups are termed schools. Schooling is therefore one of the behaviors exhibited by fish in shoals, and schools have a structure measured in polarity and synchrony" (p. 365).Miller and Gerlai [6,7] studied the temporal dynamics of shoal organization in zebrafish (Danio rerio), specifically how the average distance among fish in the shoal changes and oscillates through time in the presence of food and predators. To that end, they tracked in 2D individual fishes in an experimental group of 16 using specific video-analysis software to obtain inter-individual distances by sampling one frame per second during 1-min intervals. As some fishes were frequently observed to swim away from the main group, thus inflating the average distance, they devised an objective method [7] for deciding which individuals could be considered members of the shoal, so that only distances among these fish would be taken into account when the average was calculated and, consequently, deflated. Recently, Miller and Gerlai [8] presented a new method based on the statistical distribution of nearest neighbor distances; unlike their 5 previous method, which toke the momentary spatial distribution of the individuals into account only, the new one was based on trajectories, and defined group-membership thresholds based on how distances evolve throughout the session. They studied how individual excursions (i.e., out of the shoal) drive the shoal dissolution, and how the locat...