Optimal group size in a highly social mammal

Group size is an important trait of social animals, affecting how individuals allocate time and use space, and influencing both an individual’s fitness and the collective, cooperative behaviors of the group as a whole. Here we tested predictions motivated by the ecological constraints model of group size, examining the effects of group size on ranging patterns and adult female glucocorticoid (stress hormone) concentrations in five social groups of wild baboons (Papio cynocephalus) over an 11-y period. Strikingly, we found evidence that intermediate-sized groups have energetically optimal space-use strategies; both large and small groups experience ranging disadvantages, in contrast to the commonly reported positive linear relationship between group size and home range area and daily travel distance, which depict a disadvantage only in large groups. Specifically, we observed a U-shaped relationship between group size and home range area, average daily distance traveled, evenness of space use within the home range, and glucocorticoid concentrations. We propose that a likely explanation for these U-shaped patterns is that large, socially dominant groups are constrained by within-group competition, whereas small, socially subordinate groups are constrained by between-group competition and predation pressures. Overall, our results provide testable hypotheses for evaluating group-size constraints in other group-living species, in which the costs of intra- and intergroup competition vary as a function of group size.

Download Full-text

Experimental disturbances reveal group-level costs of social instability

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2018.1577 ◽

2018 ◽

Vol 285 (1891) ◽

pp. 20181577 ◽

Cited By ~ 17

Author(s):

A. A. Maldonado-Chaparro ◽

G. Alarcón-Nieto ◽

J. A. Klarevas-Irby ◽

D. R. Farine

Keyword(s):

Social Relationships ◽

Group Living ◽

Foraging Efficiency ◽

Social Stability ◽

Group Foraging ◽

Social Instability ◽

Living Species ◽

Important Trait ◽

Time Away ◽

Animal Societies

In group-living species, social stability is an important trait associated with the evolution of complex behaviours such as cooperation. While the drivers of stability in small groups are relatively well studied, little is known about the potential impacts of unstable states on animal societies. Temporary changes in group composition, such as a social group splitting and recombining (i.e. a disturbance event), can result in individuals having to re-establish their social relationships, thus taking time away from other tasks such as foraging or vigilance. Here, we experimentally split socially stable groups of captive zebra finches ( Taeniopygia guttata ), and quantified the effects of repeated disturbance events on (1) group foraging efficiency, and (2) co-feeding associations when subgroups were recombined. We found that the efficiency of groups to deplete a rich, but ephemeral, resource patch decreased after just a single short disturbance event. Automated tracking of individuals showed that repeated disturbances reduced efficiency by causing social relationships to become more differentiated and weaker, resulting in fewer individuals simultaneously accessing the patch. Our experiment highlights how short-term disturbances can severely disrupt social structure and group functionality, revealing potential costs associated with group instability that can have consequences for the evolution of animal societies.

Download Full-text

The effect of boldness on decision-making in barnacle geese is group-size-dependent

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2010.2266 ◽

2010 ◽

Vol 278 (1714) ◽

pp. 2018-2024 ◽

Cited By ~ 31

Author(s):

Ralf H. J. M. Kurvers ◽

Vena M. A. P. Adamczyk ◽

Sipke E. van Wieren ◽

Herbert H. T. Prins

Keyword(s):

Decision Making ◽

Group Size ◽

Group Living ◽

Decision Making Process ◽

Central Question ◽

Size Dependent ◽

Collective Decisions ◽

Living Species ◽

Barnacle Geese

In group-living species, decisions made by individuals may result in collective behaviours. A central question in understanding collective behaviours is how individual variation in phenotype affects collective behaviours. However, how the personality of individuals affects collective decisions in groups remains poorly understood. Here, we investigated the role of boldness on the decision-making process in different-sized groups of barnacle geese. Naive barnacle geese, differing in boldness score, were introduced in a labyrinth in groups with either one or three informed demonstrators. The demonstrators possessed information about the route through the labyrinth. In pairs, the probability of choosing a route prior to the informed demonstrator increased with increasing boldness score: bolder individuals decided more often for themselves where to go compared with shyer individuals, whereas shyer individuals waited more often for the demonstrators to decide and followed this information. In groups of four individuals, however, there was no effect of boldness on decision-making, suggesting that individual differences were less important with increasing group size. Our experimental results show that personality is important in collective decisions in pairs of barnacle geese, and suggest that bolder individuals have a greater influence over the outcome of decisions in groups.

Download Full-text

Group size and composition influence collective movement in a highly social terrestrial bird

eLife ◽

10.7554/elife.59902 ◽

2020 ◽

Vol 9 ◽

Author(s):

Danai Papageorgiou ◽

Damien Roger Farine

Keyword(s):

Home Range ◽

Group Size ◽

Collective Intelligence ◽

Group Living ◽

Home Range Size ◽

Range Size ◽

Collective Movement ◽

Information Pooling ◽

Movement Characteristics ◽

Group Size And Composition

A challenge of group-living is to maintain cohesion while navigating through heterogeneous landscapes. Larger groups benefit from information pooling, translating to greater ‘collective intelligence’, but face increased coordination challenges. If these facets interact, we should observe a non-linear relationship between group size and collective movement. We deployed high-resolution GPS tags to vulturine guineafowl from 21 distinct social groups and used continuous-time movement models to characterize group movements across five seasons. Our data revealed a quadratic relationship between group size and movement characteristics, with intermediate-sized groups exhibiting the largest home-range size and greater variation in space use. Intermediate-sized groups also had higher reproductive success, but having more young in the group reduced home-range size. Our study suggests the presence of an optimal group size, and composition, for collective movement.

Download Full-text

Breaking down population density into different components to better understand its spatial variation

BMC Ecology and Evolution ◽

10.1186/s12862-021-01809-6 ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Mickaël Jacquier ◽

Jean-Michel Vandel ◽

François Léger ◽

Jeanne Duhayer ◽

Sylvia Pardonnet ◽

...

Keyword(s):

Population Density ◽

Spatial Variation ◽

Group Size ◽

Social Group ◽

Local Population ◽

Group Living ◽

Density Variation ◽

Genetic Identification ◽

Population Densities ◽

Living Species

Abstract Background Population size and densities are key parameters in both fundamental and applied ecology, as they affect population resilience to density-dependent processes, habitat changes and stochastic events. Efficient management measures or species conservation programs thus require accurate estimates of local population densities across time and space, especially for continuously distributed species. For social species living in groups, population density depends on different components, namely the number of groups and the group size, for which relative variations in space may originate from different environmental factors. Whether resulting spatial variations in density are mostly triggered by one component or the other remains poorly known. Here, we aimed at determining the magnitude of the spatial variation in population densities of a social, group-living species, i.e. the European badger Meles meles, in 13 different sites of around 50 km2 across France, to decipher whether sett density, group size or proportion of occupied sett variation is the main factor explaining density variation. Besides the intrinsic factors of density variation, we also assessed whether habitat characteristics such as habitat fragmentation, urbanisation, and resource availability, drove both the spatial variation of density components and local population densities. Results We proposed a new standardised approach combining use of multiple methods, namely distance sampling for estimating the density of occupied sett clusters, i.e. group density, and camera and hair trapping for genetic identification to determine the mean social group size. The density of adult badgers was on average 3.8 per km2 (range 1.7–7.9 per km2) and was positively correlated with the density of sett clusters. The density of adult badgers per site was less related to the social group size or to the proportion of occupied sett clusters. Landscape fragmentation also explained the spatial variation of adult badger density, with highly fragmented landscapes supporting lower adult densities. Density components were linked differently to environmental variables. Conclusions These results underline the need to break down population density estimates into several components in group-living species to better understand the pattern of temporal and spatial variation in population density, as different components may vary due to different ecological factors.

Download Full-text

Subjective Fear Dilutes as Group Size Increases

10.31234/osf.io/r2yhn ◽

2020 ◽

Author(s):

dean mobbs ◽

Ellen Tedeschi ◽

Anastasia Buyalskaya ◽

Brian Silston

Keyword(s):

Group Size ◽

Real World ◽

Survival Benefit ◽

Group Living ◽

External Factors ◽

Threat Perception ◽

Perception Of Threat ◽

Threat Level ◽

Internal States ◽

Risk Dilution

According to Hamilton’s Selfish Herd Theory, a crucial survival benefit of group living is that it provides a ‘risk dilution’ function against predation. Despite a large literature on group living benefits in animals, few studies have been conducted on how group size alters subjective fear or threat perception in humans, and on what factors drive preferences for being in groups when facing threats. We conducted seven experiments (N=3,838) to test (A) if the presence of others decreases perception of threat under a variety of conditions. In studies 1 to 3, we experimentally manipulated group size in hypothetical and real-world situations, to show that fear responses decreased as group size increased. In studies 4 to 7 we again used a combination of hypothetical, virtual and real-world decisions to test (B) how internal states (e.g. anxiety) and external factors (e.g. threat level, availability of help) affected participants’ preference for groups. Participants consistently chose larger groups when threat and anxiety were high. Overall, our findings show that group size provides a salient signal of protection and safety.

Download Full-text

Faculty Opinions recommendation of Analytic steady-state space use patterns and rapid computations in mechanistic home range analysis.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.718429729.793495836 ◽

2014 ◽

Author(s):

Mark Lewis ◽

Jonathan Potts

Keyword(s):

Steady State ◽

Home Range ◽

State Space ◽

Space Use ◽

Range Analysis ◽

Use Patterns ◽

Home Range Analysis

Download Full-text

Affiliations, aggressions and an adoption: Male–male relationships in wild bonobos

10.1093/oso/9780198728511.003.0003 ◽

2018 ◽

Author(s):

Martin Surbeck ◽

Gottfried Hohmann

Keyword(s):

Close Relationships ◽

Group Living ◽

Mate Competition ◽

Male Group ◽

Cooperative Hunting ◽

Sexual Behaviours ◽

Study Population ◽

Living Species ◽

The Way

The nature of the relationships between males is a characteristic trait of many multi-male group living species with implications for the individuals. In our study population of bonobos, certain male dyads exhibit clear preferences for ranging in the same party and sitting in proximity. These preferences are not reflected in the frequency of aggression towards each other and only to some extent in their affiliative and socio-sexual behaviours. While bonobo males at LuiKotale clearly do not benefit from close relationships in the way chimpanzee males do (cooperative hunting, territorial patrol, mate competition), some relationships might result from close associations between their mothers. In some particular situations, these male relationships can be very important as in the case of an orphan adopted by his older maternal brother. La nature des relations entre mâles est un trait caractéristique de plusieurs groupes qui ont plusieurs mâles, avec des implications au niveau d’individus. Dans notre étude des populations de bonobos, certains dyades mâles montrent une préférence à aller dans le même groupe et s’asseoir proche l’un de l’autre. Cette préférence n’est pas reflétée dans la fréquence d’agression entre eux et est seulement lié, à degrés, à leur comportements socio-sexuels et d’appartenance. Tandis que les mâles bonobos à LuiKotale ne profitent pas de leur fortes relations comme les chimpanzés mâles (chasse coopérative, patrouille territoriale, compétition pour compagnon), ils peuvent aider leur partenaires à supporter le stress de la vie en groupe et peuvent en conséquence contribuer au bien-être des individus. Quelques proches associations entre les mâles peuvent provenir d’associations entre leurs mères. Dans quelques situations particulières, ces relations mâles prouvent leur importance comme dans le cas d’un orphelin adopté par son grand frère maternel.

Download Full-text

Social ethology of the wolverine

10.1093/oso/9780198759805.003.0018 ◽

2018 ◽

Author(s):

Jeffrey P. Copeland ◽

Arild Landa ◽

Kimberly Heinemeyer ◽

Keith B. Aubry ◽

Jiska van Dijk ◽

...

Keyword(s):

Social Organization ◽

Social Interactions ◽

Resource Availability ◽

Social Behaviour ◽

Social System ◽

Group Living ◽

Field Studies ◽

Ecological Framework ◽

The Social ◽

Living Species

Social behaviour in solitary carnivores has long been an active area of investigation but for many species remains largely founded in conjecture compared to our understanding of sociality in group-living species. The social organization of the wolverine has, until now, received little attention beyond its portrayal as a typical mustelid social system. In this chapter the authors compile observations of social interactions from multiple wolverine field studies, which are integrated into an ecological framework. An ethological model for the wolverine is proposed that reveals an intricate social organization, which is driven by variable resource availability within extremely large territories and supports social behaviour that underpins offspring development.

Download Full-text