Social Group Size Research Articles

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.

Pitheciid vocal communication: what can we say about what they are saying?

The variation in ecological traits in pitheciids allows investigation of vocal communication over a range of social and acoustic circumstances. In this review paper we present a summary of the history of pitheciid vocal studies and review i) the status of our current knowledge of the vocal repertoire sizes of pitheciid primates, ii) how much do we understand about the context of different acoustic signals and iii) how can we potentially use our knowledge of vocalisations in animal welfare practices. We show trends across taxa and identify gaps in our knowledge. For instance, the repertoires described for Titi monkeys and Sakis have the expected sizes for these genera, considering their relatively small social group sizes. However, Uacari groups can contain over 100 individuals, and a larger vocal repertoire than the ones described would be expected, which could be a consequence of the fission-fusion social system where the large group divides into smaller subgroups. Nevertheless, vocal repertoires exist for only about 12% of the pitheciid species and nothing is known, for example, on call ontogeny. We hope that this review will serve as a reference point for researchers interested in investigating vocal behaviour in this primate group, thus, optimising both funding focus and, researcher’s time and effort. Also, we hope to help defining methodologies and strategies for the conservation and management of pitheciid monkeys.

Coevolution of cultural intelligence, extended life history, sociality, and brain size in primates

Explanations for primate brain expansion and the evolution of human cognition and culture remain contentious despite extensive research. While multiple comparative analyses have investigated variation in brain size across primate species, very few have addressed why primates vary in how much they use social learning. Here, we evaluate the hypothesis that the enhanced reliance on socially transmitted behavior observed in some primates has coevolved with enlarged brains, complex sociality, and extended lifespans. Using recently developed phylogenetic comparative methods we show that, across primate species, a measure of social learning proclivity increases with absolute and relative brain volume, longevity (specifically reproductive lifespan), and social group size, correcting for research effort. We also confirm relationships of absolute and relative brain volume with longevity (both juvenile period and reproductive lifespan) and social group size, although longevity is generally the stronger predictor. Relationships between social learning, brain volume, and longevity remain when controlling for maternal investment and are therefore not simply explained as a by-product of the generally slower life history expected for larger brained species. Our findings suggest that both brain expansion and high reliance on culturally transmitted behavior coevolved with sociality and extended lifespan in primates. This coevolution is consistent with the hypothesis that the evolution of large brains, sociality, and long lifespans has promoted reliance on culture, with reliance on culture in turn driving further increases in brain volume, cognitive abilities, and lifespans in some primate lineages.

The effect of social group size on feather corticosterone in the co-operatively breeding Smooth-billed Ani (Crotophaga ani): An assay validation and analysis of extreme social living.

Living closely with others can provide a myriad of fitness benefits, from shared territory defense to co-operative resource acquisition. Costs of social aggregation are not absent, however, and likely influence optimal and observed groups’ sizes in a social species. Here, we explored optimal group size in a joint-nesting cuckoo species (the Smooth-billed Ani, Crotophaga ani) using endocrine markers of stress physiology (corticosterone, or CORT). Smooth-billed Anis exhibit intense reproductive competition that is exacerbated in atypically large groups. We therefore hypothesized that intra-group competition (measured by social group size) mediates the desirability and physiological cost of social group membership in this species. To test this hypothesis, we captured 47 adult Smooth-billed Anis (31 males, 16 females) during the breeding seasons of 2012-2014 in south-western Puerto Rico, and documented social group sizes. Tail feathers were sampled and used to quantify CORT (pg/mg) in enzyme-linked immunosorbent assays (ELISAs) (n = 50). Our analyses show significant differences in feather-CORT of adults between categorical group sizes, with individuals from atypically large social groups (≥ x + 1SD) having highest mean concentrations (33.319 pg/mg), and individuals from atypically small social groups (≤ x − 1SD) having lowest mean concentrations (8.969 pg/mg). Whether reproductive competition or effort is responsible for elevated CORT in atypically large social groups, however, remains unclear. Our results suggest that living in atypically large groups is physiologically expensive and may represent an evolutionarily unstable strategy. To our knowledge, this is the first study to explore a correlation between stress physiology and group size in a joint-nesting species.

Abundance of badgers (Meles meles) in England and Wales

The European badger (Meles meles) is of considerable interest in the UK as it is both a protected species and the main wildlife reservoir for bovine tuberculosis infection in cattle. While there have been three national badger surveys in the 1980s, 1990s and 2011–13, using the number of badger main setts as a proxy for the abundance of badger social groups, none has combined contemporary data on social group size at landscape and national scales. We estimated social group size by genotyping hair samples collected at 120 main setts across England and Wales and employing a capture-mark-recapture method based on genotypes. The estimated mean social group size in England and Wales was 6.74 (±0.63) badgers. There was considerable variation in badger social group size among Land Class Groups (LCGs), with a low of 2.67 in LCG3 and a high of 7.92 in LCG4. Combining these results with the recent Badger Sett Survey of England and Wales, we estimate there are approximately 485,000 badgers (95% confidence intervals 391,000–581,000) in England and Wales. Although direct comparison with previous estimates is not ideal owing to methodological differences, our results are consistent with a marked increase in the badger population of England and Wales since the 1980s.

Evaluation of an aversion-based program designed to reduce predation of native birds by dogs: An analysis of training records for 1156 dogs

The aim of this study was to quantify 1647 aversion training sessions involving 1156 dogs conducted between 1998 and 2007 at Coromandel sites (North Island, New Zealand). The effects of gender, age, social group size, function of dog, breed, number of training sessions and responses to training were explored for evidence of learning differences. The behaviour of dogs presented for up to five further training sessions was analysed for change with repeated exposure. The effect of one-, two- or three-year gaps between training sessions was also investigated. All 1156 dogs displayed avoidance to the training stimuli after the first training session. When presented with the training stimuli at the second training session, 69% of the dogs displayed avoidance, 88% did so at their third training session, 86% at the fourth session and 100% at their fifth session. Where avoidance was not displayed at a repeated training session, the dog underwent aversion training again. Lower levels of avoidance to the training stimuli were seen in older dogs being trained for the first time, dogs from single-dog households, dogs used to hunt pigs, non-sporting breed dogs and dogs that have a three-year gap or longer between sessions. While the majority of dogs avoided the kiwi training stimuli, it is recommended that the ecological translation of the training stimuli be investigated.

Self-fertilization, sex allocation and spermatogenesis kinetics in the hypodermically inseminating flatworm Macrostomum pusillum.

The free-living flatworm genus Macrostomum is an emerging model system for studying the links between sex allocation, sexual selection and mating system evolution, as well as the underlying developmental and physiological mechanisms responsible for wide intra- and inter-specific variability in reproductive phenotypes. Despite compelling comparative morphological evidence of sexual diversity, detailed experimental work on reproductive behaviour and physiology in Macrostomum has so far been largely limited to just two species, M. lignano and M. hystrix, an obligate and a preferential outcrosser, respectively. In this study, we establish that a third species, M. pusillum, exhibits a combination of reproductive traits strikingly different from both of its congeners. Unlike M. lignano, we demonstrate that M. pusillum does not adjust sex allocation or the speed of spermatogenesis to the prevailing social group size. Macrostomumpusillum's relatively simple sperm morphology likely explains the short spermatogenesis duration we report, and is linked to a hypodermically inseminating mode of fertilization, which we show also means that these worms are capable of self-fertilization. Surprisingly, and unlike M. hystrix, selfing in isolated worms commences after only a short (if any) delay compared with the onset of reproduction in grouped individuals, with little evidence of differential inbreeding depression in 'isolated' progeny. These combined results suggest that, in nature, M. pusillum may be regularly selfing, in contrast to the congeners studied to date. Our findings highlight the rapid and correlated evolution of reproductive traits, and reinforce the utility of the genus Macrostomum for understanding the evolutionary and developmental mechanisms responsible for this diversity.

Using Smartphones to Collect Behavioral Data in Psychological Science

Smartphones now offer the promise of collecting behavioral data unobtrusively, in situ, as it unfolds in the course of daily life. Data can be collected from the onboard sensors and other phone logs embedded in today’s off-the-shelf smartphone devices. These data permit fine-grained, continuous collection of people’s social interactions (e.g., speaking rates in conversation, size of social groups, calls, and text messages), daily activities (e.g., physical activity and sleep), and mobility patterns (e.g., frequency and duration of time spent at various locations). In this article, we have drawn on the lessons from the first wave of smartphone-sensing research to highlight areas of opportunity for psychological research, present practical considerations for designing smartphone studies, and discuss the ongoing methodological and ethical challenges associated with research in this domain. It is our hope that these practical guidelines will facilitate the use of smartphones as a behavioral observation tool in psychological science.

Religiosity, race/ethnicity, and alcohol use behaviors in the United States.

Religiosity is a protective factor against many health problems, including alcohol use disorders (AUD). Studies suggest that religiosity has greater buffering effects on mental health problems among US Blacks and Hispanics than Whites. However, whether race/ethnic differences exist in the associations of religiosity, alcohol consumption and AUD is unclear. Using 2004-2005 NESARC data (analytic n = 21 965), we examined the relationship of public religiosity (i.e. frequency of service attendance, religious social group size), and intrinsic religiosity (i.e. importance of religious/spiritual beliefs) to frequency of alcohol use and DSM-IV AUD in non-Hispanic (NH) Blacks, Hispanics and NH Whites, and whether associations differed by self-identified race/ethnicity. Only public religiosity was related to AUD. Frequency of religious service attendance was inversely associated with AUD (NH Whites β: -0.103, p 0.05) or Hispanics (β: -0.002, p > 0.05). US adults reporting greater public religiosity were at lower risk for AUD. Public religiosity may be particularly important among NH Blacks, while intrinsic religiosity may be particularly important among NH Whites, and among Hispanics who frequently attend religious services. Findings may be explained by variation in drinking-related norms observed among these groups generally, and in the context of specific religious institutions.

Coastal latrine sites as social information hubs and drivers of river otter fission–fusion dynamics

Fission–fusion dynamics, consisting of regular shifts in the size and composition of social groups, are prevalent in animal societies and have implications for foraging success, disease and information transfer, and the fitness of individuals. Thus, the individual and environmental factors that drive social dynamics have become a focus of recent investigations. River otters, Lontra canadensis, in coastal Alaska have a plastic social system, influenced by forage fish availability. These carnivores also regularly frequent terrestrial latrine sites, where they associate and communicate through deposition of odorous substances. To investigate fission–fusion dynamics in this system we (1) deployed camera traps to record social behaviours at latrine sites and (2) attached proximity tags to quantify encounter rates among individuals. Camera detections demonstrated that most latrine visits were of single otters and small groups (2–8 individuals). Fusion events into large groups (up to 18 individuals) were infrequent. Larger groups were recorded at crossover latrines, where trails connected bodies of water, whereas social behaviour was more frequent at spatially central latrines. Visiting otters performed signalling behaviours more frequently than social behaviours, especially at crossover sites. Proximity tag data revealed that the timing of fission and fusion events coincided with latrine visits and that spatial overlap was a good predictor of social interaction. Thus, the structural and spatial features of latrines influence their function as centres of information exchange, social activity hubs and meeting places among small social units, with implications for river otter group dynamics. We conclude that shifting social and environmental conditions may lead to high communication complexity. This unique social system provides novel evidence of the role of olfactory communication in mediating social decisions.

The Influence of Social Comparison and Peer Group Size on Risky Decision-Making.

This study explores the influence of different social reference points and different comparison group sizes on risky decision-making. Participants were presented with a scenario describing an exam, and presented with the opportunity of making a risky decision in the context of different information provided about the performance of their peers. We found that behavior was influenced, not only by comparison with peers, but also by the size of the comparison group. Specifically, the larger the reference group, the more polarized the behavior it prompted. In situations describing social loss, participants were led to make riskier decisions after comparing themselves against larger groups, while in situations describing social gain, they become more risk averse. These results indicate that decision making is influenced both by social comparison and the number of people making up the social reference group.

Impact of Social Relation and Group Size in Multicast Ad Hoc Networks

This paper investigates the multicast capacity of static wireless social networks. We adopt the two-layer network model, which includes the social layer and the networking layer. In the social layer, the social group size of each source node is modeled as power-law distribution. Moreover, the rank-based model is utilized to describe the relation between source and destinations in the networking layer. Based on the two-layer network model, the probability density function (PDF) of the destination positions is analyzed and verified by numerical simulation, which is different from the traditional ad hoc networks. According to the PDF, the bound of the network capacity is derived, and we propose a Euclidean minimum-spanning-tree-based transmission scheme, which is proved to achieve the order of capacity bound for most cases. Finally, the capacity of social networks is compared to the traditional multicast ad hoc networks, which indicates that the capacity scaling performs better in social networks than traditional ones. To our best knowledge, this is the first work of analyzing the impact on the capacity of social relation and group size in multicast ad hoc networks for the rank-based model.

Relational altruism and giving in social groups

Much fundraising is done by individuals within existing social groups. Exploiting a unique dataset, we demonstrate (i) a positive relationship between social group size and the number of donations; (ii) a negative relationship between group size and the size of individual donations; (iii) no clear relationship between group size and the total amount raised. Free riding with respect to the activity being funded cannot explain the relationship between group size and donation size, since the number of social group members is only a subset of total contributors. Instead, the findings are consistent with the notion that giving in social groups is motivated by “relational altruism”.

Importance of latrine communication in European rabbits shifts along a rural-to-urban gradient.

BackgroundInformation transfer in mammalian communication networks is often based on the deposition of excreta in latrines. Depending on the intended receiver(s), latrines are either formed at territorial boundaries (between-group communication) or in core areas of home ranges (within-group communication). The relative importance of both types of marking behavior should depend, amongst other factors, on population densities and social group sizes, which tend to differ between urban and rural wildlife populations. Our study is the first to assess (direct and indirect) anthropogenic influences on mammalian latrine-based communication networks along a rural-to-urban gradient in European rabbits (Oryctolagus cuniculus) living in urban, suburban and rural areas in and around Frankfurt am Main (Germany).ResultsThe proportion of latrines located in close proximity to the burrow was higher at rural study sites compared to urban and suburban ones. At rural sites, we found the largest latrines and highest latrine densities close to the burrow, suggesting that core marking prevailed. By contrast, latrine dimensions and densities increased with increasing distance from the burrow in urban and suburban populations, suggesting a higher importance of peripheral marking.ConclusionsIncreased population densities, but smaller social group sizes in urban rabbit populations may lead to an increased importance of between-group communication and thus, favor peripheral over core marking. Our study provides novel insights into the manifold ways by which man-made habitat alterations along a rural-to-urban gradient directly and indirectly affect wildlife populations, including latrine-based communication networks.

Increased population density reduces body growth and female investment in a simultaneous hermaphrodite.

Sex allocation theory applied to hermaphrodites assumes that there is a trade off between the allocation of resources to male and female functions, within a fixed reproductive resource budget. Charnov's classic resource allocation model predicts a more female-biased sex allocation when competition among different sperm donors is low due to diminishing fitness returns for male investment. By manipulating the social group size, one automatically changes the population density at which individuals live. Increasing population density may affect reproductive allocation, leading to resource competition and/or to increased concentration of harmful metabolites. This could lead to an over- or underestimation of the individual adjustment of sex allocation responses to mating opportunities. In this article, we tested the effects of density and social group size separately on female investment and body growth (considered as proxy of the overall energy budget) in the simultaneously hermaphroditic polychaete worm Ophryotrocha diadema. We manipulated social group size (i.e., monogamous and promiscuous regimes) and density (i.e., 4 levels) using a full-factorial design, to identify the underlying factor affecting female allocation (in terms of egg production) and body growth. In contrast to findings of previous experiments, we found that an increase in population density reduced body growth and egg production of hermaphrodites irrespective of social group size. We advance the hypothesis that the increase of catabolites and oxygen consumption in high-density conditions reduces the overall resource budget and this could obscure group size effects on female fecundity.

The coevolution of innovation and technical intelligence in primates.

In birds and primates, the frequency of behavioural innovation has been shown to covary with absolute and relative brain size, leading to the suggestion that large brains allow animals to innovate, and/or that selection for innovativeness, together with social learning, may have driven brain enlargement. We examined the relationship between primate brain size and both technical (i.e. tool using) and non-technical innovation, deploying a combination of phylogenetically informed regression and exploratory causal graph analyses. Regression analyses revealed that absolute and relative brain size correlated positively with technical innovation, and exhibited consistently weaker, but still positive, relationships with non-technical innovation. These findings mirror similar results in birds. Our exploratory causal graph analyses suggested that technical innovation shares strong direct relationships with brain size, body size, social learning rate and social group size, whereas non-technical innovation did not exhibit a direct relationship with brain size. Nonetheless, non-technical innovation was linked to brain size indirectly via diet and life-history variables. Our findings support 'technical intelligence' hypotheses in linking technical innovation to encephalization in the restricted set of primate lineages where technical innovation has been reported. Our findings also provide support for a broad co-evolving complex of brain, behaviour, life-history, social and dietary variables, providing secondary support for social and ecological intelligence hypotheses. The ability to gain access to difficult-to-extract, but potentially nutrient-rich, resources through tool use may have conferred on some primates adaptive advantages, leading to selection for brain circuitry that underlies technical proficiency.

Inhibition in Clark's nutcrackers (Nucifraga columbiana): results of a detour-reaching test.

Inhibition (i.e. the ability to restrain ineffective responses to a given stimulus) is a good indicator of complex cognitive abilities in animals. Inhibition has been demonstrated in a broad range of mammals with foraging style and social group size identified as potential influences of this ability. Whether these ecological factors also apply to birds has not been well studied. Corvids, a family of birds well known for being able to accomplish difficult cognitive tasks often requiring inhibition, are a good model for studying inhibitory control. During this study, we measured the ability of Clark's nutcrackers (Nucifraga columbiana), a relatively non-social, food specialist corvid to exercise inhibitory control during a detour-reaching test. Individuals had to retrieve a pine nut inserted into a transparent tube through one of the side openings without pecking directly at the nut from the front of the tube. Overall, nutcrackers were able to inhibit pecking directly at the food (i.e. prepotent response), instead detouring to the side to retrieve the reward. However, the nutcrackers first required a learning period before showing inhibitory control. The nutcrackers' ability to inhibit was lower than other corvids studied to date, and we discuss the implications of this result for the role of sociality and dietary breadth for the evolution of inhibitory control.

Influence of social mixing and group size on skin lesions and mounting in organic entire male pigs

Alternatives to surgical castration are needed, due to stress and pain caused by castration of male pigs. One alternative is production of entire male pigs. However, changed behaviour of entire males compared with castrated males might adversely affect the welfare of entire males and changes in management procedures and production system might be needed. Elements from the organic pig production system might be beneficial in this aspect. The aim of this article is to investigate the effect of grouping strategy including social mixing and group size on levels of mounting behaviour and skin lesions, hypothesising that procedures that disrupt the social stability (e.g. regrouping) will have a larger negative effect in small groups compared with large groups. Approximately 1600 organic entire male pigs of the breed (Landrace×Yorkshire)×Duroc were reared in parallel in five organic herds, distributed across four batches in a 2×2 factorial design in order to test the influence of social mixing (presence or absence of social mixing at relocation) and group size (15 and 30 animals). Animals were able to socialise with piglets from other litters during the lactation period, and were all mixed across litters at weaning. A second mixing occurred at insertion to fattening pens for pigs being regrouped. Counting of skin lesions (1348 or 1124 pigs) and registration of mounting behaviour (1434 or 1258 pigs) were done on two occasions during the experimental period. No interactive effects were found between social mixing and group size on either skin lesions or mounting frequency. Herd differences were found for both mounting frequency and number of skin lesions. No association between skin lesions and mounting were revealed. Social mixing and group size were shown as interacting effects with herds on mounting frequency (P<0.0001), but with no consistent pattern across all herds. In addition, no effect of social mixing was found on mean number of skin lesions, but more lesions were observed in large groups (P<0.036). This could indicate that keeping entire male pigs in groups of 30 animals as compared with smaller groups of 15 may marginally decrease the welfare of these animals.

内蒙古典型草原区狭颅田鼠集群数量与被捕食风险的关系

PDF HTML阅读 XML下载 导出引用 引用提醒 内蒙古典型草原区狭颅田鼠集群数量与被捕食风险的关系 DOI: 10.5846/stxb201506031118 作者: 作者单位: 中国科学院生态环境研究中心城市与区域生态国家重点实验室,中国科学院生态环境研究中心城市与区域生态国家重点实验室,新疆维吾尔自治区治蝗灭鼠指挥部办公室 作者简介: 通讯作者: 中图分类号: 基金项目: 中国科学院战略生物资源科技支撑体系运行专项（野生）动物实验平台运行补助经费项目；公益性行业（农业）科研专项经费项目（201203041） Relationship between predation risk and group size of narrow-skulled vole in the typical steppe of Inner Mongolia Author: Affiliation: State Key Laboratory of Urban and Regional Ecology,Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences,State Key Laboratory of Urban and Regional Ecology,Research Center for Eco-Environmental Sciences,Chinese Academy of Sciences,Locust and Rodent Control Headerquarters of Xinjiang Uygur Autonomous Region Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:2005年9月15日-30日，在内蒙古锡林郭勒盟西乌珠穆沁旗的典型草原上研究了狭颅田鼠（Microtus gregalis）冬季集群与来自艾虎（Mustela eversmanni）的捕食风险。采用鼠洞口数量作为狭颅田鼠集群大小的指标，分析了艾虎对不同大小狭颅田鼠集群的捕食优先选择偏好。对实验样地内狭颅田鼠的洞群洞口数进行了调查统计（样地内总共涉及102个狭颅田鼠有效洞群），并计数此期间的艾虎粪便堆数以及攻击掘开狭颅田鼠洞群的情况。运用非参数的Mann-Whitney U 检验法进行数据分析，结果表明：从艾虎遗留的粪便痕迹来看，没有被艾虎访问过的田鼠洞群与被艾虎访问过的洞群之间差异达到极显著水平；另外，从狭颅田鼠洞口被艾虎掘开的痕迹来分析，没有被艾虎挖掘的洞群与被艾虎挖掘的洞群之间的差异也达到极显著的水平；另外，随着田鼠洞群洞口数量的增加，出现艾虎粪便和掘洞的频次和概率就越高。表明艾虎对狭颅田鼠集群洞口数的选择差异性非常显著，明显倾向于选择在洞口数量多的狭颅田鼠洞群停留，同时也更倾向于掘开洞口数量较高的狭颅田鼠洞群作为捕食对象。 Abstract:Group sizes of overwintering colonies of narrow-skulled voles (Microtus gregalis) may affect predation risk by mammals. We examined the effect of different social group sizes on the predation risk of narrow-skulled voles in the Xilinguole typical steppe, Inner Mongolia, West Ujimqin Banner, from September 15 to 30, 2005. Furthermore, we examined the effects of predation by the steppe polecat (Mustela eversmanni) on the group size of the narrow-skulled vole within the sampling area. The number of narrow-skulled vole colonies was used to estimate group sizes of voles. The number fecal droppings and holes excavated by steppe polecats within the habitat of each narrow-skulled vole colony were recorded as indicators of predation pressure. A total of 102 voles were observed within the sampling area. The nonparametric Mann-Whitney U test was used to detect differences in social group sizes between the colonies with and without signs of polecat activity. The results showed that the rank sum of the colonies not surrounded by polecat feces was 3273.5, whereas colonies surrounded by polecat feces was 1,979.5 (U=113.5, Adjusted Z Value=-6.387, Adjusted P < 0.001). The rank sum of colonies with holes dug by polecats was 556, whereas the rank sum of colonies without the polecat excavation was 4697 (U=41, Adjusted Z Value=-3.525, Adjusted P=0.0004). The results of the Mann-Whitney test suggested significant differences in predator preference between the two groups of colonies. In addition, the frequencies of feces and excavation trails rise with the increase of group sizes. This difference indicated that the steppe polecat significantly preferred narrow-skulled vole colonies with high group sizes. The polecats tended to spend longer periods around colonies with several burrow entrances. Some polecats even attempted to dig out such colonies, and therefore, several fecal droppings and excavation trails could be found around these colonies. This finding indicated that the colonies with larger social group sizes experienced higher predator risk. 参考文献 相似文献 引证文献