scholarly journals Dissecting the two mechanisms of scramble competition among the Virunga mountain gorillas

2021 ◽  
Vol 75 (5) ◽  
Author(s):  
Andrew M. Robbins ◽  
Cyril C. Grueter ◽  
Didier Abavandimwe ◽  
Tara S. Stoinski ◽  
Martha M. Robbins
Keyword(s):  
Group Size ◽  
Scramble Competition ◽  
Ecological Constraints ◽  
Mountain Gorillas ◽  
Total Travel Time ◽  
Group Members ◽  
Per Capita ◽  
Travel Studies ◽  
The Individual ◽  
Group Travel

Abstract Two mechanisms have been proposed to explain why scramble competition can increase the travel requirements of individuals within larger groups. Firstly, individuals in larger groups may be more likely to encounter food sites where other group members have already eaten, leading to greater asynchronous “individual” travel to find fresh sites. Secondly, when food sites are aggregated into patches, larger groups may need to visit more patches to obtain the same amount of food per capita, leading to greater synchronous “group” travel between patches. If the first mechanism can be mitigated by increasing group spread, then we expect the second mechanism to be more sensitive to group size. Here, we examine the individual travel and group travel of the Virunga mountain gorillas, along with potential implications for the two mechanisms of scramble competition. Asynchronous individual travel accounted for 67% of the total travel time, and the remainder arose from group travel. Group spread increased significantly for larger groups, but not enough to prevent an increase in individual travel. Contrary to expectations, group travel decreased with size among most groups, and we found only limited evidence of patch depletion that would cause the second mechanism of scramble competition. Collectively, our results illustrate how the influence of group size can differ for individual travel versus group travel, just as it differs among species for overall travel. Studies that distinguish between the two mechanisms of scramble competition may enhance our understanding of ecological constraints upon group size, including potential differences between frugivores and folivores. Significance statement Feeding competition provides insight into how group size can influence the foraging patterns of social animals, but two key mechanisms are not typically compared. Firstly, larger groups may visit more patches to access the same amount of food per capita (group travel). Secondly, their individuals may also need to move past more spots where another member has already eaten (individual travel). Contrary to expectations, we found that group travel decreased with size for most groups of mountain gorillas, which may reflect extra travel by smaller groups to avoid larger groups. Individual travel increased with size in most groups, even though gorillas in larger groups compensated by spreading out over a broader area. The two mechanisms revealed patterns that were not apparent in our previous study of overall travel. Our approach may help to explain potential differences between folivores and frugivores.

scholarly journals Fight tactics in wood ants: individuals in smaller groups fight harder but die faster

2011 ◽  
Vol 278 (1722) ◽  
pp. 3243-3250 ◽  
Author(s):  
Tim P. Batchelor ◽  
Mark Briffa
Keyword(s):  
Group Size ◽  
Negative Influence ◽  
Resource Holding Potential ◽  
Attrition Rates ◽  
Formica Rufa ◽  
Wood Ants ◽  
Social Animals ◽  
Group Members ◽  
Per Capita ◽  
The Individual

When social animals engage in inter-group contests, the outcome is determined by group sizes and individual masses, which together determine group resource-holding potential (‘group RHP’). Individuals that perceive themselves as being in a group with high RHP may receive a motivational increase and increase their aggression levels. Alternatively, individuals in lower RHP groups may increase their aggression levels in an attempt to overcome the RHP deficit. We investigate how ‘group RHP’ influences agonistic tactics in red wood ants Formica rufa . Larger groups had higher total agonistic indices, but per capita agonistic indices were highest in the smallest groups, indicating that individuals in smaller groups fought harder. Agonistic indices were influenced by relative mean mass, focal group size, opponent group size and opponent group agonistic index. Focal group attrition rates decreased as focal group relative agonistic indices increased and there was a strong negative influence of relative mean mass. The highest focal attrition rates were received when opponent groups were numerically large and composed of large individuals. Thus, fight tactics in F. rufa seem to vary with both aspects of group RHP, group size and the individual attributes of group members, indicating that information on these are available to fighting ants.

scholarly journals Group Size, Coordination, and the Effectiveness of Punishment in the Voluntary Contributions Mechanism: An Experimental Investigation

2021 ◽  
Author(s):  
Bin Xu ◽  
C. Bram Cadsby ◽  
Liangcong Fan ◽  
Fei Song
Keyword(s):  
Group Size ◽  
Group Treatment ◽  
Entire Group ◽  
Voluntary Contributions ◽  
Good Efficiency ◽  
Marginal Group ◽  
Voluntary Contributions Mechanism ◽  
Punishment Mechanism ◽  
Per Capita ◽  
The Individual

We examine the effectiveness of the individual-punishment mechanism in larger groups, comparing groups of four to groups of 40 participants. We find that the individual punishment mechanism is remarkably robust when the marginal per capita return (MPCR), i.e. the return to each participant from each dollar that is contributed, is held constant. Moreover, the efficiency gains from the punishment mechanism are significantly higher in the 40-participant than in the four-participant treatment. This is true despite the coordination problems inherent in an institution relying on decentralized individual punishment decisions in the context of a larger group. It reflects increased per capita expenditures on punishment that offset the greater coordination difficulties in the larger group. However, if the marginal group return (MGR), i.e. the return to the entire group of participants, stays constant, resulting in an MPCR that shrinks with group size, no such offset occurs and punishment loses much but not all of its effectiveness at encouraging voluntary contributions to a public good. Efficiency is not significantly different from the small-group treatment.

scholarly journals Prey synchronize their vigilant behaviour with other group members

2007 ◽  
Vol 274 (1615) ◽  
pp. 1287-1291 ◽  
Author(s):  
Olivier Pays ◽  
Pierre-Cyril Renaud ◽  
Patrice Loisel ◽  
Maud Petit ◽  
Jean-François Gerard ◽  
...  
Keyword(s):  
Predation Risk ◽  
Group Size ◽  
Prey Species ◽  
Group Members ◽  
The Individual ◽  
The Cost ◽  
Group Member

It is generally assumed that an individual of a prey species can benefit from an increase in the number of its group's members by reducing its own investment in vigilance. But what behaviour should group members adopt in relation to both the risk of being preyed upon and the individual investment in vigilance? Most models assume that individuals scan independently of one another. It is generally argued that it is more profitable for each group member owing to the cost that coordination of individual scans in non-overlapping bouts of vigilance would require. We studied the relationships between both individual and collective vigilance and group size in Defassa waterbuck, Kobus ellipsiprymnus defassa , in a population living under a predation risk. Our results confirmed that the proportion of time an individual spent in vigilance decreased with group size. However, the time during which at least one individual in the group scanned the environment (collective vigilance) increased. Analyses showed that individuals neither coordinated their scanning in an asynchronous way nor scanned independently of one another. On the contrary, scanning and non-scanning bouts were synchronized between group members, producing waves of collective vigilance. We claim that these waves are triggered by allelomimetic effects i.e. they are a phenomenon produced by an individual copying its neighbour's behaviour.

scholarly journals Group Size, Coordination, and the Effectiveness of Punishment in the Voluntary Contributions Mechanism: An Experimental Investigation

2021 ◽  
Author(s):  
Bin Xu ◽  
C. Bram Cadsby ◽  
Liangcong Fan ◽  
Fei Song
Keyword(s):  
Group Size ◽  
Group Treatment ◽  
Entire Group ◽  
Voluntary Contributions ◽  
Good Efficiency ◽  
Marginal Group ◽  
Voluntary Contributions Mechanism ◽  
Punishment Mechanism ◽  
Per Capita ◽  
The Individual

We examine the effectiveness of the individual-punishment mechanism in larger groups, comparing groups of four to groups of 40 participants. We find that the individual punishment mechanism is remarkably robust when the marginal per capita return (MPCR), i.e. the return to each participant from each dollar that is contributed, is held constant. Moreover, the efficiency gains from the punishment mechanism are significantly higher in the 40-participant than in the four-participant treatment. This is true despite the coordination problems inherent in an institution relying on decentralized individual punishment decisions in the context of a larger group. It reflects increased per capita expenditures on punishment that offset the greater coordination difficulties in the larger group. However, if the marginal group return (MGR), i.e. the return to the entire group of participants, stays constant, resulting in an MPCR that shrinks with group size, no such offset occurs and punishment loses much but not all of its effectiveness at encouraging voluntary contributions to a public good. Efficiency is not significantly different from the small-group treatment.

Individual Contributions To Cooperative Behaviour in the Acorn Woodpecker: Effects of Reproductive Status, Sex, and Group Size

Behaviour ◽  
1985 ◽  
Vol 95 (3-4) ◽  
pp. 290-312 ◽  
Author(s):  
Ronald L. Mumme ◽  
Alan De Queiroz
Keyword(s):  
Group Size ◽  
Common Interest ◽  
Cooperative Behaviour ◽  
Individual Fitness ◽  
Strong Positive Relationship ◽  
Individual Contributions ◽  
Melanerpes Formicivorus ◽  
Group Members ◽  
Acorn Woodpeckers ◽  
The Individual

AbstractAcorn woodpeckers (Melanerpes formicivorus) are communal breeders that live in permanently territorial family groups of 2-15 individuals. All group members participate in several forms of cooperative behaviour, which we define as the investment of resources in a common interest shared by other group members (CHASE, 1980). Acorn woodpecker group interests include the caching of acorns in a specialized storage tree (the granary), maintenance of the granary, and defence of the granary against intra- and interspecific intruders. Because of a strong positive relationship between the availability of stored acorns and group reproductive success, investments in acorn storage, granary maintenance, and granary defence have a direct positive effect on the individual fitness of breeders. Non-breeding helpers, however, do not realize a direct reproductive reward, and therefore profit less directly from investment in these forms of cooperative behaviour. Thus, we predicted that breeders should invest more heavily in cooperative behaviour than should helpers. The prediction was upheld: for nearly every form of cooperative behaviour examined, breeders contribute significantly more than do helpers. On the other hand, while established breeders only rarely intrude on neighbouring territories, nonreproductive helpers frequently do so. These dispersal "forays" constitute attempts by helpers to locate ecologically restricted breeding vacancies. The effect that group size has on individual contributions to cooperative behaviour is unclear. Individual rates of acorn storage decrease significantly with increasing group size, but granary attendance and granary maintenance do not. Male and female acorn woodpeckers do not differ in their contributions to acorn storage, granary maintenance, or interspecific defence. Females, however, play a significantly greater role in intraspecific defence because of a female-biased intruder sex ratio and sex-specific defensive behaviour.

scholarly journals Red deer Cervus elaphus blink more in larger groups

2020 ◽  
Author(s):  
Zeke W. Rowe ◽  
Joseph H. Robins ◽  
Sean A. Rands
Keyword(s):  
Group Size ◽  
Cervus Elaphus ◽  
Red Deer ◽  
Group Living ◽  
Blink Rate ◽  
Non Invasive ◽  
Group Members ◽  
The Individual ◽  
Perceived Predation Risk ◽  
Meaningful Measure

ABSTRACTMost animals need to spend time being vigilant for predators, at the expense of other activities such as foraging. Group-living animals can benefit from the shared vigilance effort of other group members, with individuals reducing personal vigilance effort as group size increases. Behaviours like active scanning or head lifting are usually used to quantify vigilance, but may not be accurate measures as the individual could be conducting them for other purposes. We suggest that measuring an animal’s blinking rate gives a meaningful measure of vigilance: increased blinking implies reduced vigilance, as the animal cannot detect predators when its eyes are closed. We demonstrate that as group size increases in red deer, individuals increase their blink rate, confirming the prediction that vigilance should decrease. Blinking is a simple non-invasive measure, and offers a useful metric for assessing the welfare of animals experiencing an increase in perceived predation risk or other stressors.

The Epistemology of Groups

2020 ◽  
Author(s):  
Jennifer Lackey
Keyword(s):  
Group Level ◽  
Social Significance ◽  
Individual Group ◽  
Key Concepts ◽  
Normative Requirements ◽  
Group Members ◽  
The Individual ◽  
Belief Justification ◽  
In Virtue Of ◽  
Trump Administration

Groups are often said to bear responsibility for their actions, many of which have enormous moral, legal, and social significance. The Trump Administration, for instance, is said to be responsible for the U.S.’s inept and deceptive handling of COVID-19 and the harms that American citizens have suffered as a result. But are groups subject to normative assessment simply in virtue of their individual members being so, or are they somehow agents in their own right? Answering this question depends on understanding key concepts in the epistemology of groups, as we cannot hold the Trump Administration responsible without first determining what it believed, knew, and said. Deflationary theorists hold that group phenomena can be understood entirely in terms of individual members and their states. Inflationary theorists maintain that group phenomena are importantly over and above, or otherwise distinct from, individual members and their states. It is argued that neither approach is satisfactory. Groups are more than their members, but not because they have “minds of their own,” as the inflationists hold. Instead, this book shows how group phenomena—like belief, justification, and knowledge—depend on what the individual group members do or are capable of doing while being subject to group-level normative requirements. This framework, it is argued, allows for the correct distribution of responsibility across groups and their individual members.

scholarly journals Group size and aquatic vegetation modulates male preferences for female shoals in wild zebrafish, Danio rerio

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Aditya Ghoshal ◽  
Anuradha Bhat
Keyword(s):  
Group Size ◽  
Aquatic Vegetation ◽  
Natural Habitat ◽  
Ecological Factors ◽  
Choice Test ◽  
Female Group ◽  
Aquatic Flora ◽  
In The Wild ◽  
The Individual

AbstractShoaling decisions in the wild are determined by a combination of innate preferences of the individual along with the interplay of multiple ecological factors. In their natural habitat as well as in the laboratory, zebrafish is a shoaling fish. Here, we investigate the role of group size and associated vegetation in shaping shoaling preferences of wild male zebrafish. We studied the association preference of males to groups of female shoals in a multi-choice test design. We found that males made greater proportion of visits to an 8-female group compared to 2 and 4-female groups. However, males spent similar proportions of time across the three female-containing groups. When artificial vegetation was incorporated along with female number as an additional factor, we found that males prefer high and moderately vegetated patches compared to low or no-vegetation groups, irrespective of the number of females in these patches. Based on experiments using a novel multi-choice design, our results show that preference for group size can change due to interaction of two separate factors. This work is a first attempt to understand the role of aquatic flora in determining shoaling preferences in zebrafish, using an experimental paradigm consisting of a gradation in female and vegetation densities.

scholarly journals The triple aim of clinical research

2021 ◽  
pp. 174077452110015
Author(s):  
E Ray Dorsey ◽  
Karl Kieburtz
Keyword(s):  
Health Care ◽  
Clinical Research ◽  
Population Health ◽  
Patient Experience ◽  
Triple Aim ◽  
Per Capita ◽  
The Individual

The proposed triple aim of health care—enhanced patient experience, improved population health, and reduced per capita costs—can be applied to clinical research. A triple aim for clinical research would (1) improve the individual research participant’s experience; (2) promote the health of populations; and (3) reduce per capita costs of clinical research. Such an approach is possible by designing trials around the needs of participants rather than sites, embracing digital measures of health, and advancing decentralized studies. Recent studies, including those evaluating therapies for COVID-19, have demonstrated the value of such an approach. Accelerating the adoption of these methods can help fulfill this new triple aim of clinical research.

Estimating Express Train Preference of Urban Railway Passengers Based on Extreme Gradient Boosting (XGBoost) using Smart Card Data

2021 ◽  
pp. 036119812110133
Author(s):  
Eun Hak Lee ◽  
Kyoungtae Kim ◽  
Seung-Young Kho ◽  
Dong-Kyu Kim ◽  
Shin-Hyung Cho
Keyword(s):  
Travel Time ◽  
Smart Card ◽  
Public Transportation ◽  
Gradient Boosting ◽  
Log Data ◽  
Smart Card Data ◽  
Extreme Gradient Boosting ◽  
Express Train ◽  
Total Travel Time ◽  
The Individual

As the share of public transport increases, the express strategy of the urban railway is regarded as one of the solutions that allow the public transportation system to operate efficiently. It is crucial to express the urban railway’s express strategy to balance a passenger load between the two types of trains, that is, local and express trains. This research aims to estimate passengers’ preference between local and express trains based on a machine learning technique. Extreme gradient boosting (XGBoost) is trained to model express train preference using smart card and train log data. The passengers are categorized into four types according to their preference for the local and express trains. The smart card data and train log data of Metro Line 9 in Seoul are combined to generate the individual trip chain alternatives for each passenger. With the dataset, the train preference is estimated by XGBoost, and Shapley additive explanations (SHAP) is used to interpret and analyze the importance of individual features. The overall F1 score of the model is estimated to be 0.982. The results of feature analysis show that the total travel time of the local train feature is found to substantially affect the probability of express train preference with a 1.871 SHAP value. As a result, the probability of the express train preference increases with longer total travel time, shorter in-vehicle time, shorter waiting time, and few transfers on the passenger’s route. The model shows notable performance in accuracy and provided an understanding of the estimation results.

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