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  1. Foundational work has examined adaptive social behavior in animals in relation to the costs and benefits of group living. Within this context, a “group” of animals represents an organizational unit that is integral to the study of animal ecology and evolution.
  2. Definitions of animal group sizes are often subjective with considerable variability within and across species. However, investigations of both the extent and implications of such variability in the estimation of animal group sizes are currently lacking.
  3. Selecting ungulates as a case study, we conducted a literature review to assess prevailing practices used to determine group sizes among terrestrial Cetartiodactyla and Perissodactyla. Via this process, we examined group size definitions for 61 species across 171 peer‐reviewed studies published between 1962 and 2018.
  4. These studies quantified group sizes via estimation of ungulate aggregations in space and time. Spatial estimates included a nearest neighbor distance ranging from 1.4 m to 1,000 m, and this variation was partially explained by a weak positive correlation (|r| = .4, p < .003) with the body size of the ungulate research subjects. The temporal extent over which group size was estimated was even broader, ranging from three minutes to 24 hr.
  5. The considerable variability in ungulate group size estimation that we observed complicates efforts to not only compare and replicate studies but also to evaluate underlying theories of group living. We recommend that researchers: (a) clearly describe the spatiotemporal extents over which they define ungulate group sizes, (b) highlight foundational empirical and ecological rationale for these extents, and (c) seek to align such extents among individual species so as to facilitate cross‐system comparisons of ungulate group size dynamics. We believe an integrative approach to ungulate group size estimation would readily facilitate replication, comparability, and evaluation of competing hypotheses examining the tradeoffs of animal sociality.
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Social interactions of adult female sable antelope, Hippotragus niger, were observed at the National Zoological Park's Conservation and Research Center. Aggressive behavior was quantified for two herds containing 8 and 11 females. Aggression was lowest at calving, and highest near the time of conception. Dominance hierarchies were strictly linear and stable over time. Dominance rank was highly correlated with age, with the oldest females achieving highest rank. High-ranking females initiated more aggression and were more likely to behave aggressively towards a newly introduced adult female. The newly introduced individual was the victim of prolonged, intense group chases and was permanently excluded from the herd. Low-ranking females directed more aggression at yearling herd members than did high-ranking females. Temporary absences by herd members resulted in long-lasting, substantial increases in received aggression upon their return. Because of their aggressive nature, sable antelope present a challenge to captive management. © 1993 Wiley-Liss, Inc.  相似文献   

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Group-living animals travel together to collectively exploit the resources of their environment. This study investigates how social relationships and individual temperament traits affect movement orders in domestic cattle and sheep. We analysed spontaneous group movements occurring at pasture after a resting period in a group of 15 18-month-old Charolais heifers and a group of 19 1-year-old Romane ewe-lambs. For each species, animals had similar social experience and no kinship ties. Before that, animals were observed within the group to establish their social status (e.g. dominance and preferential relationships, and sociability), then in individual tests in order to assess their emotional traits. In both species, most individuals could initiate a group movement but some individuals were more successful than others in recruiting the rest of the group. Ewe-lambs, and to a lesser extent heifers, held preferential positions during travel. We did not find any significant correlations in either species between animal order and their position in the dominance hierarchy (heifers: P = 0.438; ewe-lambs: P = 0.574) while individuals linked by preferential bonds frequently followed each other during group movements (heifers: P < 0.001; ewe-lambs: P < 0.001). With regard to social traits, heifers with a low cohesion index, and with a lower number of partners with whom they develop frequent affinitive interactions, acted more frequently as 'first movers' (P = 0.040 and 0.023, respectively), as well as did ewe-lambs with a high spatial independency index (P = 0.002). Ewe-lambs with the highest cohesion indices were more frequently observed in front of the group while moving halfway between departure and arrival (P = 0.028). We did not find significant correlations between individual positions during group movements and emotional traits such as reactivity, boldness and fearfulness. We conclude that preferential bonds and individual traits related to social dependence were more influential in spontaneous group movements at pasture than were emotional traits and dominance status.  相似文献   

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The ‘human shield hypothesis’ describes the situation where prey species use humans as shield from natural predation. We tested the human shield hypothesis in a population of mountain nyala (Tragelaphus buxtoni) subjected to predation from the nocturnal spotted hyena (Crocuta Crocuta) in the Bale Mountains National Park, Ethiopia by radio‐marking 15 mountain nyala (seven females and eight males) and tracking them for up to 2 yr. Occurrence of hyena estimated by faecal transects decreased close to human settlements substantiating the occurrence of a zone with lower risk of hyena predation. The diurnal pattern in the average distance between mountain nyala relocations and human settlements was consistent with the human shield hypothesis with significantly shorter distances during night (when exposed to predation) than during day. However, mountain nyala showed large individual heterogeneity in use of human shields. While nearly all individuals occasionally moved out of the park to human settlements during night, the frequency of such excursions varied from 0% to 71%. The excursions occurred year‐round and were not driven by seasonal access to crops. We have previously demonstrated a strong negative effect of humans on the large‐scale distribution pattern of mountain nyala. The use of human shield documented here is indicative of a positive small‐scale effect of humans. Our study thus supports the view that the effect of human–wildlife interactions can be scale‐dependent.  相似文献   

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We examined the importance of sex differences in predation risk in generating sexual segregation in the guppy, Poecilia reticulata. We hypothesised that sex differences in predation risk will result in habitat segregation and ultimately social segregation of the sexes, with the more vulnerable sex (males in this case) using safer habitats. In accordance with the predation risk hypothesis we observed sexual segregation in a population associated with high but not low predation risk. Under high predation risk we observed a larger proportion of males in shallow marginal habitats resulting in habitat segregation and ultimately social segregation of the sexes. Furthermore, habitat segregation by sex was associated with habitat segregation by body length with shoals in deeper water having a larger mean body length. Shoaling fish species have been key models in investigating group living, and further research directed towards understanding sexual segregation in other fish species would be valuable.  相似文献   

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Population densities of yellow-handed titi monkey (Callicebus torquatus) were estimated using transect census methods. Densities were 2.8 individuals/km(2 )in the upper Rio Itaya basin and 2.5 individuals/km(2) in the lower Rio Algodón basin. Group size varied from two to five individuals, with an average of 2.9 individuals per group at the Rio Itaya. Groups were generally composed of two adults, probably the reproductive pair, with progeny from one to three previous birth seasons. Although the Rio Itaya population is phenotypically identical to populations from the rivers Nanay and Tigre, it differs from population on the rivers Napo and Putumayo. This suggests the existence of two disjunct populations of C. torquatus in Peruvian Amazonia whose taxonomic status warrants further examination.  相似文献   

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Because primates display such remarkable diversity, they are an ideal taxon within which to examine the evolutionary significance of group living and the ecological factors responsible for variation in social organization. However, as with any social vertebrate, the ecological determinants of primate social variability are not easily identified. Interspecific variation in group size and social organization results from the compromises required to accommodate the associative and dissociative forces of many factors, including predation, 1 - 3 conspecific harassment and infanticide, 4 - 6 foraging competition 1 , 7 and cooperation, 8 dominance interactions, 9 reproductive strategies, and socialization. 10 - 12 Causative explanations have emerged primarily through the construction of theoretical models that organize the observed variation in primate social organization and group size relative to measurable ecological variation.  相似文献   

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The increased abundance of large carnivores in Europe is a conservation success, but the impact on the behavior and population dynamics of prey species is generally unknown. In Europe, the recolonization of large carnivores often occurs in areas where humans have greatly modified the landscape through forestry or agriculture. Currently, we poorly understand the effects of recolonizing large carnivores on extant prey species in anthropogenic landscapes. Here, we investigated if ungulate prey species showed innate responses to the scent of a regionally exterminated but native large carnivore, and whether the responses were affected by human‐induced habitat openness. We experimentally introduced brown bear Ursus arctos scent to artificial feeding sites and used camera traps to document the responses of three sympatric ungulate species. In addition to controls without scent, reindeer scent Rangifer tarandus was used as a noncarnivore, novel control scent. Fallow deer Dama dama strongly avoided areas with bear scent. In the presence of bear scent, all ungulate species generally used open sites more than closed sites, whereas the opposite was observed at sites with reindeer scent or without scent. The opening of forest habitat by human practices, such as forestry and agriculture, creates a larger gradient in habitat openness than available in relatively unaffected closed forest systems, which may create opportunities for prey to alter their habitat selection and reduce predation risk in human‐modified systems that do not exist in more natural forest systems. Increased knowledge about antipredator responses in areas subjected to anthropogenic change is important because these responses may affect prey population dynamics, lower trophic levels, and attitudes toward large carnivores. These aspects may be of particular relevance in the light of the increasing wildlife populations across much of Europe.  相似文献   

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Proboscis monkey (Nasalis larvatus) socioecology was studied at the Natai Lengkuas Station, Tanjung Puting National Park, in Kalimantan Tengah, Indonesia. Data on the nature of intergroup interactions were collected on ten one-male groups and two all-male groups using event sampling during follows and also through evening census surveys. Proboscis monkeys form stable one-male groups, with specific groups regularly associating at their sleeping sites (band members). Both intraband and interband high-intensity agonistic displays (slapping, chasing, biting) were rare. Lower intensity agonistic displays (vocalizations, leaping-branch shaking, and erect penis and open-mouth displays) occurred frequently. Temporal avoidance between bands may have been mediated by early morning vocalizations and branch shaking displays by the adult males. Associations between groups may play a role in displacement avoidance and/or predation avoidance.  相似文献   

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We examined the spatial and temporal distribution of the foods of ursine colobus (Colobus vellerosus) at Boabeng-Fiema, Ghana as a means to predict the monopolizablity and usurpability of their food resources. Recent evidence suggests that food may not be limiting for folivorous primates, and that male sexual coercion may be a more important influence on folivore social organization. To address the question, we collected focal data on the feeding behavior of adult females and males over 11 mo (September 2000-August 2001) on 2 groups: WW (n = 31–33 individuals) and B (n = 8–16 individuals). We also conducted phenological monitoring and a tree survey of the two-group home ranges to establish food availability and distribution. We used 2 behavioral or organism-defined indicators of feeding behavior to assess potential resource contestability: food site residence time and distance moved between food sites. The colobus fed on a high diversity of species, most of their food trees were not clumped in distribution, within-tree interfood distances were short, and food trees were large. The only condition associated with the potential for monopolization was low food tree density. However, low food tree density may be offset by the colobus’ use of large trees. Taken together, the ecological and behavioral indicators suggest the food resources of Colobus vellerosus had a low potential for monopolization. Our results also indicate mature leaves had the longest food site residence time, which may suggest they should be the most usurpable plant part, though their presumed low quality and high abundance probably counteracted the effect. The pattern implied the potential for direct feeding competition among Colobus vellerosus at Boabeng-Fiema was low and agonistic interactions over food are not expected. Instead, a group size effect on feeding efficiency should be a more predominant influence on feeding efficiency, if food is limiting for the species.  相似文献   

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Fear of predation alters prey behavior, which can indirectly alter entire landscapes. A parasite‐induced ecology of fear might also exist if animals avoid parasite‐contaminated resources when infection costs outweigh foraging benefits. To investigate whether animals avoid parasite contaminated sites, and if such avoidance balances disease costs and foraging gains, we monitored animal behavior at raccoon latrines – sites that concentrate both seeds and pathogenic parasite eggs. Using wildlife cameras, we documented over 40 potentially susceptible vertebrate species in latrines and adjacent habitat. Latrine contact rates reflected background activity, diet preferences and disease risk. Disease‐tolerant raccoons and rats displayed significant site attraction, while susceptible birds and small mammals avoided these high‐risk sites. This suggests that parasites, like predators, might create a landscape of fear for vulnerable hosts. Such non‐consumptive parasite effects could alter disease transmission, population dynamics, and even ecosystem structure.  相似文献   

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Roan antelope are distributed mainly in regions characterized by infertile soils, offering food of low quality. We hypothesized that roan may select localities with higher soil nutrient levels and/or grass swards with more favourable properties in terms of food abundance or quality than generally available in those regions. Roan antelope were observed in a savanna region in South Africa where soils of widely varying nutrient status occurred. Roan favoured open grassland over wooded savanna areas. During the wet season, roan preferred sites with felsite‐derived soil of intermediate soil nutrient status. Grasslands growing on nutrient enriched alluvial soils were preferred outside of the early wet season, although most of the favourable sward characteristics were present in other landscape units. Food quantity, rather than quality appeared to attract roan to foraging sites in the late wet and early dry seasons. Food quality appeared more important in the early wet and late dry seasons. The higher degree of clustering of leafy material within foraging swards seemed to be an additional discriminating factor. The factors governing the selection of foraging sites by roan did not seem notably different from those influencing other species of grazing ruminant, but roan nevertheless seemed tolerant of stemmy grasslands growing on nutrient richer substrates.  相似文献   

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We investigated the consistency of association network structure for groups of sticklebacks Gasterosteus aculeatus. Each group was observed twice and we varied the duration between observations and the size of the experimental arena that they were observed in. At the dyad level, we found positive correlations between dyad interaction frequencies across observations. At the group level we found variation in four network metrics between observations, but only in treatments where the duration between observations was short. Specifically, fish formed more and smaller groups in the second observation in this treatment. Fish were also organized into more subunits in the larger arenas. Finally, we saw positive correlations between some group network metrics across observations suggesting relative consistency at the group level. There are several processes that might drive these interaction patterns. Our findings have implications for experimental design and the comparison and integration of findings of experiments from different studies carried out under different conditions.  相似文献   

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The group size effect states that animals living in groups gain anti‐predator benefits through reducing vigilance levels as group size increases. A basic assumption of group size effect is that all individuals are equally important for a focal individual, who may adjust its vigilance levels according to social information acquired from them. However, some studies have indicated that neighbors pose greater influences on an individual's vigilance decisions than other group members, especially in large aggregations. Vigilance has also been found to be directed to both predators (anti‐predation vigilance) and conspecifics (social vigilance). Central individuals might rely more on social vigilance than peripheral individuals. To test these hypotheses, we examined the effects of flock size, number of neighbors and position within a flock on vigilance and competition of greater white‐fronted goose Anser albifrons that form large foraging flocks in winter, controlling the effects of other variables (group identity, winter period and site). We found that individual vigilance levels were significantly affected by number of neighbors and position within a flock, whereas flock size showed no effect. Individuals devoted a large component of vigilance to nearby flock mates. Central individuals directed a relatively larger proportion of vigilance to monitor neighbors than peripheral ones, indicating that central individuals more relied on social information acquired from neighbors, possibly caused by the more blocked visual field of central individuals. Moreover, some social vigilance may function as conducting or preventing agonistic interactions since competition intensity was positively correlated with number of neighbors. Our study therefore demonstrate that the number of neighbors is more important than group size in determining individual vigilance in large animal groups. Further studies are still needed to unravel which neighbors pose greater influence on individual vigilance, and the factors that influence individuals to acquire information from their neighbors to adjust vigilance behaviors.  相似文献   

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《Current biology : CB》2021,31(17):3952-3955.e3
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Recent research has shown that large flamingo flocks are more likely to experience reproductive success than small flocks and that there is a positive relationship between behavioral stimulation from group displays and reproductive success. This study compares the group displays and reproductive success in a captive flock of Caribbean flamingos over 6 years at the National Zoological Park. Birds were added to the flock in two different years. In each case, the flock produced fertile eggs during the breeding season following the addition of new birds. Furthermore, the addition of new birds in 1988, and then again in 1991, significantly increased group display activity over the previous year when the flock size was lower. That the addition of birds stimulated group display activity suggests an alternative management strategy for promoting reproduction in captivity: separate birds in a flock and then reunite them prior to the breeding season. © 1994 Wiley-Liss, Inc.  相似文献   

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