Social Group Size Research Articles

Host anemone size as a determinant of social group size and structure in the orange clownfish (Amphiprion percula).

The size and structure of social groups of animals can be governed by a range of ecological factors and behavioral interactions. In small, highly site-attached coral reef fishes, group size is often constrained by the size of the habitat patch they are restricted to. However, group size may also be influenced by changes in abundance along important environmental gradients, such as depth or distance offshore. In addition, the body size and sex structure within social groups can be determined by the size of the habitat patch and the dominance relationships among group members. Here we examined the roles of ecological factors and behavioral interactions in governing group size and structure in the orange clownfish, Amphiprion percula, on inshore reefs in Kimbe Bay, Papua New Guinea. We quantified relationships between ecological variables (anemone size, depth, and distance from shore) and social group variables (group size, and total body length of the three largest individuals (ranks 1, 2, and 3)). Anemone size explained the greatest amount of variation in group variables, with strong, positive relationships between anemone surface area and group size, and total length of individuals ranked 1, 2, and 3. Group structure was also weakly correlated with increasing depth and distance from shore, most likely through the indirect effects of these environmental gradients on anemone size. Variation in group size and the lengths of ranks 2 and 3 were all closely related to the length of rank 1. Path analysis indicated that anemone size has a strong direct effect on the length of rank 1. In turn, the length of rank 1 directly affects the size of the subordinate individuals and indirectly affects the group size through its influence on subordinates. Hence, anemone size directly and indirectly controls social group size and structure in this space-limited fish species. It is also likely that anemonefish have feedback effects on anemone size, although this could not be differentiated in the path analysis.

A Pilot Observational Study of Environmental Summertime Health Risk Behavior in Central Brisbane, Queensland: Opportunities to Raise Sun Protection Awareness in Australia's Sunshine State.

Melanoma skin cancer rates in Queensland exceed the national Australian incidence rate, which together with New Zealand are recognized as the world's highest. Incidence is especially high among younger members of the population. In this study, the sun-protective behaviors of urban Queenslanders (n=752) going about their day-to-day activities during a midweek noon time hourly period were observed on a summer's day in central Brisbane (27.47°S, 153.03°E), Australia. Observed sun protection practices were poor, given the time of year and peak solar noon period of the study. More individuals (n=249; 33.1%) were seen wearing sunglasses than a hat (n=101; 13.4%). Ninety-three individuals were actively engaging with mobile phones (phone in hand). A further 231 individuals (30.7%) were observed with a mobile phone on them. Opportunities to modify group behavior based on mobile phone sun protection notifications and to engage with "at risk" members of the Queensland population are considered from the variable codependencies examined in this study, including the influence of social group size, observed sun protection and mobile phone use. Our preliminary findings suggest that mobile phones provide an underutilized opportunity for delivering tailored skin cancer prevention messaging.

The flexible socio spatial group queries

A socio spatial group query finds a group of users who possess strong social connections with each other and have the minimum aggregate spatial distance to a meeting point. Existing studies limit to either finding the best group of a fixed size for a single meeting location, or a single group of a fixed size w.r.t. multiple locations. However, it is highly desirable to consider multiple locations in a real-life scenario in order to organize impromptu activities of groups of various sizes. In this paper, we propose Top k Flexible Socio Spatial Group Query (Top k-FSSGQ) to find the top k groups w.r.t. multiple POIs where each group follows the minimum social connectivity constraints. We devise a ranking function to measure the group score by combining social closeness, spatial distance, and group size, which provides the flexibility of choosing groups of different sizes under different constraints. To effectively process the Top k-FSSGQ, we first develop an Exact approach that ensures early termination of the search based on the derived upper bounds. We prove that the problem is NP-hard, hence we first present a heuristic based approximation algorithm to effectively select members in intermediate solution groups based on the social connectivity of the users. Later we design a Fast Approximate approach based on the relaxed social and spatial bounds, and connectivity constraint heuristic. Experimental studies have verified the effectiveness and efficiency of our proposed approaches on real datasets.

Group size effects in social evolution

How the size of social groups affects the evolution of cooperative behaviors is a classic question in evolutionary biology. Here we investigate group size effects in the evolutionary dynamics of games in which individuals choose whether to cooperate or defect and payoffs do not depend directly on the size of the group. We find that increasing the group size decreases the proportion of cooperators at both stable and unstable rest points of the replicator dynamics. This implies that larger group sizes can have negative effects (by reducing the amount of cooperation at stable polymorphisms) and positive effects (by enlarging the basin of attraction of more cooperative outcomes) on the evolution of cooperation. These two effects can be simultaneously present in games whose evolutionary dynamics feature both stable and unstable rest points, such as public goods games with participation thresholds. Our theory recovers and generalizes previous results and is applicable to a broad variety of social interactions that have been studied in the literature.

Fitness benefits and emergent division of labour at the onset of group living.

The initial fitness benefits of group-living are considered the greatest hurdle to the evolution of sociality1, and theory predicts that they need to arise at very small group sizes2. Such benefits are thought to emerge partly from scaling effects that increase efficiency as group size increases3–5. In social insects and other taxa, they have been proposed to stem from division of labor (DOL)5–8, which is characterized by between-individual variability and within-individual consistency (specialization) in task performance. At the onset of sociality, however, groups were likely small and composed of similar individuals with potentially redundant rather than complementary function1. Theory suggests that DOL can emerge even in relatively small, simple groups9,10. However, empirical data on the effects of group size on DOL and fitness remain equivocal6. Here, we use long-term automated behavioral tracking in clonal ant colonies, combined with mathematical modeling, to show that increases in social-group size can generate DOL among extremely similar workers, in groups as small as six individuals. These early effects on behavior were associated with large increases in homeostasis—the maintenance of stable conditions in the colony11— and per capita fitness. Our model suggests that increases in homeostasis are primarily driven by increases in group size itself, and, to a smaller extent, by higher DOL. Overall, our results indicate that DOL, increased homeostasis, and higher fitness can naturally emerge in small, homogeneous social groups, and that scaling effects associated with increasing group size can thus promote social cohesion at incipient stages of group-living.

Sociality does not drive the evolution of large brains in eusocial African mole-rats

The social brain hypothesis (SBH) posits that the demands imposed on individuals by living in cohesive social groups exert a selection pressure favouring the evolution of large brains and complex cognitive abilities. Using volumetry and the isotropic fractionator to determine the size of and numbers of neurons in specific brain regions, here we test this hypothesis in African mole-rats (Bathyergidae). These subterranean rodents exhibit a broad spectrum of social complexity, ranging from strictly solitary through to eusocial cooperative breeders, but feature similar ecologies and life history traits. We found no positive association between sociality and neuroanatomical correlates of information-processing capacity. Solitary species are larger, tend to have greater absolute brain size and have more neurons in the forebrain than social species. The neocortex ratio and neuronal counts correlate negatively with social group size. These results are clearly inconsistent with the SBH and show that the challenges coupled with sociality in this group of rodents do not require brain enlargement or fundamental reorganization. These findings suggest that group living or pair bonding per se does not select strongly for brain enlargement unless coupled with Machiavellian interactions affecting individual fitness.

Shoal size as a key determinant of vulnerability to capture under a simulated fishery scenario.

Group living is widespread among animals and has a range of positive effects on individual foraging and predator avoidance. For fishes, capture by humans constitutes a major source of mortality, and the ecological effects of group living could carry‐over to harvest scenarios if fish are more likely to interact with fishing gears when in social groups. Furthermore, individual metabolic rate can affect both foraging requirements and social behaviors, and could, therefore, have an additional influence on which fish are most vulnerable to capture by fishing. Here, we studied whether social environment (i.e., social group size) and metabolic rate exert independent or interactive effects on the vulnerability of wild zebrafish (Danio rerio) to capture by a baited passive trap gear. Using video analysis, we observed the tendency for individual fish to enter a deployed trap when in different shoal sizes. Fish in larger groups were more vulnerable to capture than fish tested individually or at smaller group sizes. Specifically, focal fish in larger groups entered traps sooner, spent more total time within the trap, and were more likely to re‐enter the trap after an escape. Contrary to expectations, there was evidence that fish with a higher SMR took longer to enter traps, possibly due to a reduced tendency to follow groupmates or attraction to conspecifics already within the trap. Overall, however, social influences appeared to largely overwhelm any link between vulnerability and metabolic rate. The results suggest that group behavior, which in a natural predation setting is beneficial for avoiding predators, could be maladaptive under a trap harvest scenario and be an important mediator of which traits are under harvest associated selection.

An experimental test of effects of ambient temperature and roost quality on aggregation by little brown bats (Myotis lucifugus)

Environmental factors, such as ambient temperature (Ta) or roost/nest quality, can influence social behaviour of small-bodied endotherms because individuals may aggregate for social thermoregulation when Ta is low or select the warmest possible sites for roosting. Female temperate bats form maternity colonies in spring to communally raise pups and exploit social thermoregulation. They also select roosts with warm microclimates because low roost temperature (Troost) delays juvenile development. We studied captive female little brown bats (Myotis lucifugus) to test the hypothesis that variation in Ta and Troost influence social group size. First, we predicted that female bats would preferentially select artificially heated roosts over unheated roosts. Second, we predicted that, as Ta decreased, group size would increase because bats would rely more heavily on social thermoregulation. Third, we predicted that experimentally increasing Troost (i.e., roost quality) above Ta would result in larger group sizes due to greater aggregation in high quality roosts. We captured 34 females from a maternity colony and housed them in a flight-tent provisioned with four bat boxes. Each box was outfitted with a heating pad and thermostat. Over the course of eight-days we heated each roost box in sequence to near thermoneutral Troost for two days. Bats preferentially selected heated roosts over unheated roosts but, contrary to our prediction, group size decreased when Troost was much greater than Ta (i.e., when the benefits of a warm roost should have been highest). Our results suggest that social thermoregulation and the availability of warm roosts influence aggregation in bats and have implications for the potential of summer habitat protection and enhancement to help bat populations in the face of threats like white-nose syndrome.

Achievable Capacity Scaling Laws of Three-Dimensional Wireless Social Networks

With the development of aeronautical telecommunication and unmanned aerial vehicles (UAVs), wireless networks will be extended to three-dimensional (3-D) space. Besides, 3-D wireless networks have been widely deployed in battlefields, which consist of aircraft, UAVs, ground troops, and fleets. When nodes in these wireless networks form swarm and cooperate with each other, there will be social behavior among them and 3-D wireless social networks emerge. Although the study of wireless social networks has been initiated, the capacity of 3-D wireless social networks is unknown. In this paper, we derive the achievable capacity of 3-D wireless social networks. It shows that the capacity is a function of the pathloss exponent, the number of nodes, the social group concentration, the contact concentration, and the size of social group. When the social group concentration or the contact concentration exceeds a threshold, the wireless social network is scalable and the capacity of wireless social network is much larger than that of the wireless network without social behavior. Besides, we discover the existence of a singular point for social group concentration and contact concentration, where the network capacity skips to a larger value than the neighborhood. The results reveal the interplay between wireless communication and social connection in 3-D space, which brings an insight into the design of 3-D wireless networks.

Functional Morphology of Mimetic Musculature in Primates: How Social Variables and Body Size Stack up to Phylogeny.

Mammalian skeletal muscle is influenced by the functional demands placed upon it. Functional morphology of facial expression musculature, or mimetic musculature, is largely unknown. Recently, primate mimetic musculature has been shown to respond to demands associated with social factors. Body size has also been demonstrated to affect many aspects of primate functional morphology and evolutionary morphology. The present study was designed to further examine the role of social variables and body size in influencing the morphology of primate mimetic musculature using a broad phylogenetic range of primates, primates with varying body sizes, and those that exploit differing time of day activity cycles and social group sizes. Gross data on mimetic musculature morphology were gathered from tarsiers (Tarsius bancanus), slender lorises (Loris tardigradus), ring-tailed lemurs (Lemur catta), crowned lemurs (Eulemur coronatus), black lemurs (E. macaco), owl monkeys (Aotus trivirgatus), and howler monkeys (Alouatta caraya) and compared to previous results from chimpanzees (Pan troglodytes), gibbons and siamangs (hylobatids), rhesus macaques (Macaca mulatta), Sulawesi macaques (M. nigra), common marmosets (Callithrix jacchus), and greater bushbabies (Otolemur spp.). Mimetic muscle presence/absence was observed and recorded. Results revealed that phylogenetic position determines the overall mimetic muscle groundplan, with anthropoids having a high number of muscles in the superciliary and midface regions, strepsirrhines having a high number of muscles in the external ear region, and tarsiers displaying an intermediate condition. Within these broad taxonomic categories body size had an effect on mimetic musculature, while time of day activity and social group size had smaller effects. Anat Rec, 301:202-215, 2018. © 2018 Wiley Periodicals, Inc.

Impact of Social Interaction on the Capacity of Hybrid Wireless Networks

In this paper, we jointly consider the optimal max- $L$ -hops routing policy and social features for the throughput capacity of a hybrid wireless network, which is different from the existing works that ignored the network traffic model. For the social feature, each node’s social group is determined by a probability related to the distance from the source node. To embody the features of social behavior, we propose a traffic model within a social group. Under the max- $L$ -hops routing policy in the hybrid wireless network, we analyze the effects of physical distance, clustering property, and a number of base station on throughput capacity. We also study the influence of different social group sizes on the throughput capacity. Our results demonstrate that: 1) the optimal $L$ is not only related to social group size, but also the selection of destination nodes; 2) when the social contact factors $\alpha$ and $\beta$ increase, the throughput capacity trends to be independent of the number of base station and routing parameter $L$ . Particularly, our results show that the wireless network is scalable with the number of node, if the social contact factor is large enough; and 3) the results demonstrate that the base station and social interaction improve the throughput capacity of hybrid wireless networks.

The path to cooperative action during group social dilemmas: A literature review, set of propositions, and model describing how the opportunity to communicate encourages cooperation

A social dilemma is a circumstance in which each of an aggregate of people must make an individual decision whether to acquire a short-term benefit for themselves or to forego some of that benefit for the long-term benefit of the aggregate. The intent of this essay is to describe how communication, in terms of both the opportunity to talk and the content of what is said, interacts with other “cooperative mechanisms” – group identity, reciprocity and equity norms, and trust and trustworthiness – to largely determine individual cooperation versus defection. Two variables with relatively complex impacts on the cooperative mechanisms – social value orientation and group size – are also discussed. A model and set of propositions relating these variables are also included, and areas for further are explored.

Social Value Orientation and Group Size Uncertainty in Public Good Dilemmas

Risk and uncertainty are an integral part of everyday human interactions. Recent literature has shown that group size uncertainty might change strategic cooperation behavior in significant ways. In this paper, we investigate how conditional cooperation changes under group size uncertainty in a linear public good game where the selfish rational strategy is kept constant. Further, we suggest an underlying mechanism that consists of beliefs and group size estimation. We show that interpersonal differences (i.e., Social Value Orientation) are essential in how this mechanism operates. More specifically, we find that prosocials contribute more under uncertainty compared to certainty, whereas proselfs do not change their behavior. Given the same feedback proselfs estimated the group size to be bigger than prosocials, resulting in a smaller contribution belief. These results imply that interpersonal differences are important in explaining cooperation under uncertainty compared to certainty.

Group Size Effects in Social Evolution

How the size of social groups affects the evolution of cooperative behaviors is a classic question in evolutionary biology. Here we investigate group size effects in evolutionary games in which individuals choose whether to cooperate or defect. We find that increasing the group size decreases the proportion of cooperators at both stable and unstable rest points of the replicator dynamics. This implies that larger group sizes can have negative effects (by reducing the amount of cooperation at stable polymorphisms) and positive effects (by enlarging the basin of attraction of more cooperative outcomes) on the evolution of cooperation. These two effects can be simultaneously present in games whose evolutionary dynamics features both stable and unstable rest points, such as public goods games with participation thresholds. Our theory recovers and generalizes previous results and is applicable to a broad variety of social interactions that have been studied in the literature.

Primate social group sizes exhibit a regular scaling pattern with natural attractors.

Primate groups vary considerably in size across species. Nonetheless, the distribution of mean species group size has a regular scaling pattern with preferred sizes approximating 2.5, 5, 15, 30 and 50 individuals (although strepsirrhines lack the latter two), with a scaling ratio of approximately 2.5 similar to that observed in human social networks. These clusters appear to form distinct social grades that are associated with rapid evolutionary change, presumably in response to intense environmental selection pressures. These findings may have wider implications for other highly social mammal taxa.

Social security: are socially connected individuals less vigilant?

Group size effects, whereby animals allocate less time to antipredator vigilance as a function of increasing numbers of animals foraging together, are reported in many taxa, but group size is but one of many social attributes that could increase an individual's perception of predation risk or what might be referred to as a ‘sense of security’. Indeed, meta-analyses suggest that group size only explains a small amount of variation in vigilance, and studies have shown that other social attributes, such as dominance status, also influence perceived risk and time allocated to vigilance. Social network analysis is an emerging technique to quantify a variety of specific social attributes, some of which have been suggested to influence ‘security’. Using the proportion of time looking as an indicator of vigilance and predation risk assessment, we tested the prediction that more socially connected yellow-bellied marmots, Marmota flaviventer, look less while foraging compared to their less socially connected counterparts. For females and males separately, we used observational data to create intrasexual, weighted social networks. We used principal component analysis to reduce correlated measures to unrelated and independent descriptions of connectedness. Using linear mixed effect models to account for potentially confounding variables, we found that no social network measure explained variation in vigilance. Social group size explained variation in female vigilance after accounting for variation due to vegetation height and date. Foraging group size and vegetation height explained variation in male vigilance. While social network measures themselves were not significant, our results mirror the fact that yellow-bellied marmots live in female-dominated societies and suggest that overall social group size is relatively more important for females than for males. Systematically studying whether and how social factors and intrasexual social relationships influence antipredator behaviour in other animals will create a better understanding of the benefits of sociality.

Reading wild minds: A computational assay of Theory of Mind sophistication across seven primate species.

Theory of Mind (ToM), i.e. the ability to understand others' mental states, endows humans with highly adaptive social skills such as teaching or deceiving. Candidate evolutionary explanations have been proposed for the unique sophistication of human ToM among primates. For example, the Machiavellian intelligence hypothesis states that the increasing complexity of social networks may have induced a demand for sophisticated ToM. This type of scenario ignores neurocognitive constraints that may eventually be crucial limiting factors for ToM evolution. In contradistinction, the cognitive scaffolding hypothesis asserts that a species' opportunity to develop sophisticated ToM is mostly determined by its general cognitive capacity (on which ToM is scaffolded). However, the actual relationships between ToM sophistication and either brain volume (a proxy for general cognitive capacity) or social group size (a proxy for social network complexity) are unclear. Here, we let 39 individuals sampled from seven non-human primate species (lemurs, macaques, mangabeys, orangutans, gorillas and chimpanzees) engage in simple dyadic games against artificial ToM players (via a familiar human caregiver). Using computational analyses of primates' choice sequences, we found that the probability of exhibiting a ToM-compatible learning style is mainly driven by species' brain volume (rather than by social group size). Moreover, primates' social cognitive sophistication culminates in a precursor form of ToM, which still falls short of human fully-developed ToM abilities.

Social Class and Group Size as Predictors of Behavior in Male Equus kiang

Social Class and Group Size as Predictors of Behavior in Male Equus kiang

Re-evaluating the link between brain size and behavioural ecology in primates.

Comparative studies have identified a wide range of behavioural and ecological correlates of relative brain size, with results differing between taxonomic groups, and even within them. In primates for example, recent studies contradict one another over whether social or ecological factors are critical. A basic assumption of such studies is that with sufficiently large samples and appropriate analysis, robust correlations indicative of selection pressures on cognition will emerge. We carried out a comprehensive re-examination of correlates of primate brain size using two large comparative datasets and phylogenetic comparative methods. We found evidence in both datasets for associations between brain size and ecological variables (home range size, diet and activity period), but little evidence for an effect of social group size, a correlation which has previously formed the empirical basis of the Social Brain Hypothesis. However, reflecting divergent results in the literature, our results exhibited instability across datasets, even when they were matched for species composition and predictor variables. We identify several potential empirical and theoretical difficulties underlying this instability and suggest that these issues raise doubts about inferring cognitive selection pressures from behavioural correlates of brain size.

Social structure affects mating competition in a damselfish

The strength of mating competition and sexual selection varies over space and time in many animals. Such variation is typically driven by ecological and demographic factors, including adult sex ratio and consequent availability of mates. The spatial scale at which demographic factors affect mating competition and sexual selection may vary but is not often investigated. Here, we analyse variation in size and sex ratio of social groups, and how group structure affects mating competition, in the site-attached damselfish Chrysiptera cyanea. Site-attached reef fishes are known to show extensive intraspecific variation in social structure. Previous work has focused on species for which the size and dynamics of social groups are constrained by habitat, whereas species with group structure unconstrained by habitat have received little attention. Chrysiptera cyanea is such a species, with individuals occurring in spatial clusters that varied widely in size and sex ratio. Typically, only one male defended a nest in multi-male groups. Nest-holding males were frequently visited by mate-searching females, with more visits in groups with more females, suggesting that courtship and mating mostly occur within groups and that male mating success depends on the number of females in the group. Male–male aggression was frequent in multi-male groups but absent in single-male groups. These findings demonstrate that groups are distinct social units. In consequence, the dynamics of mating and reproduction are mainly a result of group structure, largely unaffected short term by overall population demography which would be important in open social systems. Future studies of the C. cyanea model system should analyse longer-term dynamics, including how groups are formed, how they vary in relation to density and time of season and how social structure affects sexual selection.