Ruth Dolado

Determining shoal membership: A comparison between momentary and trajectory-based methods

Miller and Gerlai proposed two methods for determining shoal membership in Danio rerio, one based on momentary mean inter-individual distances and the other on post hoc analysis of the trajectories of nearest-neighbor distances. We propose a method based on momentary nearest-neighbor distances and compare the three methods using simulation. In general, our method yielded results that were more similar to their second method than their first one, and is computationally simpler.

Determining shoal membership using affinity propagation

We propose using the affinity propagation (AP) clustering algorithm for detecting multiple disjoint shoals, and we present an extension of AP, denoted by STAP, that can be applied to shoals that fusion and fission across time. STAP incorporates into AP a soft temporal constraint that takes cluster dynamics into account, encouraging partitions obtained at successive time steps to be consistent with each other. We explore how STAP performs under different settings of its parameters (strength of the temporal constraint, preferences, and distance metric) by applying the algorithm to simulated sequences of collective coordinated motion. We study the validity of STAP by comparing its results to partitioning of the same data obtained from human observers in a controlled experiment. We observe that, under specific circumstances, AP yields partitions that agree quite closely with the ones made by human observers. We conclude that using the STAP algorithm with appropriate parameter settings is an appealing approach for detecting shoal fusion-fission dynamics.

A method for resolving occlusions when multitracking individuals in a shoal

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.

How Many for Lunch Today? Seasonal Fission-Fusion Dynamics as a Feeding Strategy in Wild Red-Capped Mangabeys (Cercocebus torquatus)

For group-living primates, social organization hinges upon multiple factors, including group size, group cohesion, and the groups 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.

Modeling the emergence of seasonal fission-fusion dynamics in red-capped mangabeys (Cercocebus torquatus)

Social systems can be defined based on their degree of fission-fusion dynamics, which depends on party characteristics (i.e., spatial cohesion, party size, and sex-age composition). Although the ecological and ethological causes of fission-fusion dynamics are still under revision, fruit availability seems to be a main factor in party formation in primates. We therefore explored ecological (i.e., fruit availability as an indicator of food competition) and ethological factors (i.e., travel distance) related to fission-fusion dynamics using our own agent-based simulation model. We compared the simulation results from the model with field data obtained from the movement patterns of a wild group of red-capped mangabeys (Cercocebus torquatus) (Dolado et al. 2016, Folia Primatol 87:197–212) and found that they were consistent with field data obtained on C. torquatus in that they showed similar patterns of seasonal fission-fusion dynamics. Moreover, the results suggest that the fission-fusion dynamics observed in simulations can match patterns of travel distance of arboreal species subject to food competition that reflects behavioral flexibility to adapt to environmental conditions shown by C. torquatus in the field.Significance statementWe have developed an agent-based model that reproduces the seasonal fission-fusion dynamics shown by a wild group of C. torquatus on the Atlantic coast of Gabon. The results of our simulations suggest that fission-fusion dynamics are an emergent behavior and that agent-based models are a good tool for exploring emergent behaviors in silico. Moreover, the agent-based simulation approach provides helpful new insights for future field studies on fission-fusion dynamics.

Agonistic Strategies and Spatial Distribution in Captive Sooty Mangabeys (Cercocebus Atys)

The aim of this article is to study the relationship between the dominance hierarchy and the spatial distribution of a group of captive sooty mangabeys (Cercocebus atys). The analysis of the spatial distribution of individuals in relation to their rank in the dominance hierarchy showed a clear linear hierarchy in which the dominant individual was located in central positions with regard to the rest of the group members. The large open enclosure where the group was living allowed them to adopt a high-risk agonistic strategy in which individuals attacked other individuals whose rank was significantly different from their own. The comparison of the results with a previous study of mangabeys showed that, although the dominance ranks of both groups were similar, the fact that they lived in facilities with different layouts caused different agonistic strategies to emerge and allowed the dominant individual to assume different spatial locations.