Factors affecting social behavior and reproductive success of male rhesus monkeys

This paper reviews aspects of life history that influence the reproductive success of male rhesus monkeys. Recent theories propose that there is some optimum level of inbreeding for each population and that behaviors related to group transfer by males are the result of selection pressure toward such an optimum. Group changing by males is clearly linked to the effects of testosterone at sexual maturation. A male’s maternal genealogical rank is not consistently related to the age at which it leaves the natal group, but social interactions within the natal group may influence the age of departure. Choice of the new group is influenced by the operational sex ratio and the presence of maternal relatives. Rank in the new group is positively correlated with seniority. Seniority, in turn, is influenced by the rank of the male’s natal group, his mother’s genealogical rank, and the presence of male siblings in the new group. Much of this effect is due to the high mortality of males born to females and/or groups of low rank. Most studies show a positive association between male reproductive success and rank. Males from high-ranking groups and/or maternal genealogies that join groups containing brothers tend to remain in those groups longer, attain a higher rank, and probably achieve higher levels of reproduction than other males.     

The effect of social facilitation on foraging success in vultures: a modelling study

The status of many Gyps vulture populations are of acute conservation concern as several show marked and rapid decline. Vultures rely heavily on cues from conspecifics to locate carcasses via local enhancement. A simulation model is developed to explore the roles vulture and carcass densities play in this system, where information transfer plays a key role in locating food. We find a sigmoid relationship describing the probability of vultures finding food as a function of vulture density in the habitat. This relationship suggests a threshold density below which the foraging efficiency of the vulture population will drop rapidly towards zero. Management strategies should closely study this foraging system in order to maintain effective foraging densities.     

Lifetime reproductive success and longevity of queens in an annual social insect

Although central to understanding life‐history evolution, the relationship between lifetime reproductive success and longevity remains uncertain in many organisms. In social insects, no studies have reported estimates of queens’ lifetime reproductive success and longevity within populations, despite the importance of understanding how sociality and associated within‐group conflict affect life‐history traits. To address this issue, we studied two samples of colonies of the annual bumblebee, Bombus terrestris audax, reared from wild‐caught queens from a single population. In both samples, queens’ lifetime reproductive success, measured as either queens’ inclusive fitness or as total biomass of queen‐produced sexuals (new queens and males), was significantly positively associated with queen longevity, measured from the day the first worker was produced. We suggest that a positive relationship between reproductive success and longevity was inherited from nonsocial ancestors showing parental care and maintained, at least in part, because the presence of workers buffers queens against extrinsic mortality.     

Agonistic reciprocity is associated with reduced male reproductive success within haremic social networks

While individual variation in social behaviour is ubiquitous and causes social groups to differ in structure, how these structural differences affect fitness remains largely unknown. We used social network analysis of replicate bluebanded goby (Lythrypnus dalli) harems to identify the reproductive correlates of social network structure. In stable groups, we quantified agonistic behaviour, reproduction and steroid hormones, which can both affect and respond to social/reproductive cues. We identified distinct, optimal social structures associated with different reproductive measures. Male hatching success (HS) was negatively associated with agonistic reciprocity, a network structure that describes whether subordinates ‘reciprocated’ agonism received from dominants. Egg laying was associated with the individual network positions of the male and dominant female. Thus, males face a trade-off between promoting structures that facilitate egg laying versus HS. Whether this reproductive conflict is avoidable remains to be determined. We also identified different social and/or reproductive roles for 11-ketotestosterone, 17β-oestradiol and cortisol, suggesting that specific neuroendocrine mechanisms may underlie connections between network structure and fitness. This is one of the first investigations of the reproductive and neuroendocrine correlates of social behaviour and network structure in replicate, naturalistic social groups and supports network structure as an important target for natural selection.     

Bumblebees (Bombus terrestris) use social information as an indicator of safety in dangerous environments

Avoiding predation is one of the most important challenges that an animal faces. Several anti-predation behaviours can be employed, yet simply using the presence of conspecifics can be a good signal of safety in an environment with potential predation hazards. Here, we show, for the first time, that past experience of predation causes bumblebees (Bombus terrestris) to aggregate with conspecifics, facilitating the identification of safe foraging patches. Bees were trained to differentiate between flowers that harboured predators and flowers that were predator free. When test subjects were subsequently presented solely with the previously predator-infested flower species, there was a significant preference to only land on flowers occupied by other feeding conspecifics. Yet, when safe flowers were made available to subjects previously entrained to discriminate safe from predator-occupied flowers, subjects ignored other bees and the social information potentially provided by them, demonstrating that attraction towards conspecifics is confined to dangerous situations. Our findings demonstrate a previously unknown social interaction in pollinators which may have important implications for plant–pollinator interactions.     

When to use social information: the advantage of large group size in individual decision making

Correct decision making is crucial for animals to maximize foraging success and minimize predation risk. Group-living animals can make such decisions by using their own personal information or by pooling information with other group members (i.e. social information). Here, we investigate how individuals might best balance their use of personal and social information. We use a simple modelling approach in which individual decisions based upon social information are more likely to be correct when more individuals are involved and their personal information is more accurate. Our model predicts that when the personal information of group members is poor (accurate less than half the time), individuals should avoid pooling information. In contrast, when personal information is reliable (accurate at least half the time), individuals should use personal information less often and social information more often, and this effect should grow stronger in larger groups. One implication of this pattern is that social information allows less well-informed members of large groups to reach a correct decision with the same probability as more well-informed members of small groups. Thus, animals in larger groups may be able to minimize the costs of collecting personal information without impairing their ability to make correct decisions.     

Validity of an estimator of reproductive success

Lifetime reproductive success is a major component of individual fitness and a central dependent variable for the study of natural selection. For long-lived animals, such as apes or baboons, assessment of lifetime reproductive success requires observations of identified individuals in continuous, long-term studies from which it is difficult and often impossible to obtain an adequate sample of necessary reproductive and survival data. This situation can be alleviated by the availability of a valid measure that uses incomplete reproductive histories to estimate the lifetime reproductive success of individuals. The validity of one such estimator was tested by determining if, after 10.5 years of studying free-ranging female baboons, it predicted lifetime reproductive success obtained from full reproductive histories after 21.5 years. Validity was evaluated for seven criteria of success, ranging from the number of a female's live births to the number of her offspring that reached the age of 72 months. Moderate to good prediction of lifetime reproductive success by the estimator was found for criteria of offspring living to 36 months or more. After 10.5 years, complete reproductive life spans were available for only eight females. Using the estimator, analytic potential, via sample representativeness and size, was improved at 10.5 years by an increase from a sample of eight to between 34 and 62, depending upon the criterion used, and at 21.5 years from 39 to 70. With a valid estimator, the opportunity to study lifetime reproductive success of a long-lived species is substantially improved without having to depend upon rarely available, uninterrupted data collection for 20–60 years. Am. J. Primatol. 44:137–145, 1998. © 1998 Wiley-Liss, Inc.     

Effects of social group size on information transfer and task allocation

Summary Social animals exchange information during social interaction. The rate of interaction and, hence, the rate of information exchange, typically changes with density and density may be affected by the size of the social group. We investigate models in which each individual may be engaged in one of several tasks. For example, the different tasks could represent alternative foraging locations exploited by an ant colony. An individual's decision about which task to pursue depends both on environmental stimuli and on interactions among individuals. We examine how group size affects the allocation of individuals among the various tasks. Analysis of the models shows the following. (1) Simple interactions among individuals with limited ability to process information can lead to group behaviour that closely approximates the predictions of evolutionary optimality models, (2) Because per capita rates of social interaction may increase with group size, larger groups may be more efficient than smaller ones at tracking a changing environment, (3) Group behaviour is determined both by each individual's interaction with environmental stimuli and by social exchange of information. To keep these processes in balance across a range of group sizes, organisms are predicted to regulate per capita rates of social interaction and (4) Stochastic models show, at least in some cases, that the results described here occur even in small groups of approximately ten individuals.     

Dolphin social intelligence: complex alliance relationships in bottlenose dolphins and a consideration of selective environments for extreme brain size evolution in mammals

Bottlenose dolphins in Shark Bay, Australia, live in a large, unbounded society with a fission-fusion grouping pattern. Potential cognitive demands include the need to develop social strategies involving the recognition of a large number of individuals and their relationships with others. Patterns of alliance affiliation among males may be more complex than are currently known for any non-human, with individuals participating in 2-3 levels of shifting alliances. Males mediate alliance relationships with gentle contact behaviours such as petting, but synchrony also plays an important role in affiliative interactions. In general, selection for social intelligence in the context of shifting alliances will depend on the extent to which there are strategic options and risk. Extreme brain size evolution may have occurred more than once in the toothed whales, reaching peaks in the dolphin family and the sperm whale. All three 'peaks' of large brain size evolution in mammals (odontocetes, humans and elephants) shared a common selective environment: extreme mutual dependence based on external threats from predators or conspecific groups. In this context, social competition, and consequently selection for greater cognitive abilities and large brain size, was intense.     

Species interactions and population density mediate the use of social cues for habitat selection

1. The perspective that populations and communities are structured by antagonistic interactions among individuals has dominated much of ecology. Yet how animals use social information to guide decisions, such as habitat selection, may be influenced by both positive and negative interactions among individuals. Recent theory also suggests that the way animals use social information may be substantially influenced by population density, which alters the potential costs and benefits of such behaviours. 2. I manipulated cues of two competitors, the dominant least flycatcher Empidonax minimus (Baird & Baird) and the subordinate American redstart Setophaga ruticilla (Linnaeus), to assess the use of conspecific and heterospecific cues during habitat selection, and if population density influences these strategies. The experiment consisted of surveying birds during a pre-treatment year, which allows for the control and testing the effect of baseline densities, and a treatment year, in which treatments were applied just prior to settlement. Treatments included broadcasting songs of flycatchers and redstarts, and were compared with controls. 3. When controlling for pre-treatment densities, bird densities, and to a lesser extent arrival dates, during the treatment year suggested that flycatchers were attracted to both conspecific and heterospecific cues during settlement. Furthermore, attraction was strongest for flycatchers in plots with moderate pre-treatment densities. American redstarts were rare in the study area but showed apparent attraction to conspecifics and avoidance of heterospecifics. 4. These results provide experimental evidence for the use of multiple social cues in habitat selection and suggest that heterospecific attraction may operate under broader contexts than originally envisioned. In such instances, nontarget effects can potentially occur when manipulating social cues to elicit settlement in conservation strategies. The impact of population density on the use of social cues shown here can also influence our understanding of metapopulation dynamics by causing complex threshold effects on the likelihood of rescue, which may influence metapopulation stability and the likelihood of local extinction.     

Group size,composition, and reproductive success in wild common marmosets (Callithrix jacchus)

Data from published sources about size and composition of wild common marmoset groups (Callithrix jacchus) were analyzed to see if the number of juveniles in a group is closely related to the number of other group members. Mean group size was 8.7 members including 4.4 adults (1.8 females, 2.5 males), 2.9 subadults, and 1.4 juveniles. The number of juveniles was significantly positively correlated to the number of adult males. Groups with one or two adult males had significantly fewer juveniles (mean: 1:1 juveniles) than groups containing more than two adult males (mean: 2.0 juveniles). Apart from a different number of subadults, results showed obvious similarities between common marmosets and tamarins of the genus Saguinus in size and composition of subgroups of adults as well as the key role of adult males in mediating the reproductive success of a breeding female. Common marmoset females seem to gain direct fitness benefits in increased reproductive success from the presence of a larger number of adult males. Whether or not other group members get fitness benefits depends on the reproductive strategy of adult males (monogamy vs. polyandry), their kinship, and on the genetic relationship of nonbreeders to the offspring of the breeding female. © 1995 Wiley-Liss, Inc.     

Flamingo breeding: The role of group displays

Group displays in flamingos have been presumed to play a role in stimulating synchronous nesting and in facilitating pair formation. This study compares the group displays and breeding success of a captive flock of Caribbean flamingos (Phoenicopterus ruber ruber) at the National Zoological Park between 2 years: the frequency and synchrony of group displays were measured for a flock of 17 in 1988 and then again in 1989 after flock size was increased to 21. In 1989 the rate of occurrence of display activity increased 48%, the synchrony of group displays increased 100%, the frequency of mounts and copulations almost doubled, and for the first time in the flock's history two fertile eggs were produced. The use of sprinklers to simulate rain had no effect on the group displays. The amount of naturally occurring rainfall in 1989 was almost twice that in 1988. The increased frequency and synchrony of group displays could be attributed to increased flock size, change in sex ratio, addition of strange individuals, or increased rainfall. This study, however, provides evidence for a relationship between behavioral stimulation from group displays and components of breeding success in flamingos.     

Colony size,social complexity and reproductive conflict in social insects

The broad limits of mature colony size in social insect species are likely to be set by ecological factors. However, any change in colony size has a number of important social consequences. The most fundamental is a change in the expected reproductive potential of workers. If colony size rises, workers experience a fall in their chances of becoming replacement reproductives and, it is shown, increasing selection for mutual inhibition of one another's reproduction (worker policing). As workers’ reproductive potential falls, the degree of dimorphism between reproductive and worker castes (morphological skew) can rise. This helps explain why small societies have low morphological skew and tend to be simple in organization, whereas large societies have high morphological skew and tend to be complex. The social consequences of change in colony size may also alter colony size itself in a process of positive feedback. For these reasons, small societies should be characterized by intense, direct conflict over reproduction and caste determination. By contrast, conflict in large societies should predominantly be over brood composition, and members of these societies should be relatively compliant to manipulation of their caste. Colony size therefore deserves fuller recognition as a key determinant, along with kin structure, of social complexity, the reproductive potential of helpers, the degree of caste differentiation, and the nature of within-group conflict.     

Factors affecting the reproductive success of dominant male meerkats

Identifying traits that affect the reproductive success of individuals is fundamental for our understanding of evolutionary processes. In cooperative breeders, a dominant male typically restricts mating access to the dominant female for extended periods, resulting in pronounced variation in reproductive success among males. This may result in strong selection for traits that increase the likelihood of dominance acquisition, dominance retention and reproductive rates while dominant. However, despite considerable research on reproductive skew, few studies have explored the factors that influence these three processes among males in cooperative species. Here we use genetic, behavioural and demographic data to investigate the factors affecting reproductive success in dominant male meerkats (Suricata suricatta). Our data show that dominant males sire the majority of all offspring surviving to 1 year. A male's likelihood of becoming dominant is strongly influenced by age, but not by weight. Tenure length and reproductive rate, both important components of dominant male reproductive success, are largely affected by group size and composition, rather than individual traits. Dominant males in large groups have longer tenures, but after this effect is controlled, male tenure length also correlates negatively to the number of adult females in the group. Male reproductive rate also declines as the number of intra- and extra-group competitors increases. As the time spent in the dominant position and reproductive rate while dominant explain > 80% of the total variance in reproductive success, group composition thus has major implications for male reproductive success.     

Social status and reproductive success of male Macaca fascicularis

Dominant males of nonseasonally breeding species should have more opportunity than seasonal breeders to monopolize access to estrous females and thus enhance their reproductive success. They may also use other strategies for maximizing reproductive success such as producing offspring by relatively high ranking females. To test these hypotheses, the paternity of 35 (80%) of 44 Macaca fascicularis offspring, born over a 28-month period, was established using electrophoretically and serologically defined genetic markers. The social ranks of each of the seven potential fathers and 26 potential mothers were determined by recording outcomes of dyadio agonistic interactions. No evidence could be found to support either hypothesis. Further, in view of previously reported significant, positive correlations between male social rank and sexual activity rates in this study group, sexual activity rates do not appear to predict the number of offspring a male sires in this species.