Vigilance and Group Size in Homo sapiens

While eating, Homo sapiens frequently look up and visually scan their environment. As in many bird and mammal species studied, the frequency of looking up was negatively correlated with group size. Average duration of scanning the environment also correlated negatively with group size. At all group sizes studied (1–5), females spent less time scanning than did males. With increasing group size females reduced their rate of looking up more than did males.     

Local survival in Semipalmated Sandpipers Calidris pusilla breeding at La Pérouse Bay, Canada

A hierarchical modelling approach was used to examine adult and age-specific survival in an 8-year study of breeding Semipalmated Sandpipers Calidris pusilla at La Pérouse Bay, Canada. The survival of adult sandpipers was best described by a model with time dependence in local survival rate and probability of recapture. Annual variation in the local survival rate of adults was not correlated with nest success, timing of breeding or "return rates" and was not biased by an effect of first capture. Local survival rate of adult females (0.56, 95% c.l. = 0.51-0.61) was consistently lower than that of adult males (0.61, 95% c.l. = 0.56-0.66); these estimates were comparable with data from other shorebirds. The survival of returning young was best fitted by a model with both age and time dependence in local survival rate and probability of recapture. We evaluated our estimates of local survival rate with reference to patterns of breeding fidelity and philopatry in Semipalmated Sandpipers and other shorebirds.     

Effect of Group Size on Individual and Collective Vigilance in Greater Rheas

We studied the effect of group size on the proportion of time that greater rheas, Rhea americana, allocated to vigilance and feeding during the non‐breeding season. We tested whether: (1) the proportion of time that one bird allocates to vigilance (individual vigilance) decreases with group size, and (2) the proportion of time that at least one bird of the group is vigilant (collective vigilance) increases with group size. We analyzed video‐recordings of birds that were foraging alone or in groups from two to 12 birds. The proportion of time allocated to individual vigilance decreased and the proportion of time spent feeding increased with group size. In both cases the main significant difference was between birds foraging alone and in groups. Collective vigilance did not vary with group size and it was lower than expected if vigilance bouts were random or sequential. Our results indicate that rheas foraging in large groups would not receive the benefit of an increase in collective vigilance, although they could still benefit from a reduction of predation risk by the dilution effect.     

On the Relationship between Herbaceous Cover and Vigilance Activity of Degus (Octodon degus)

A number of studies demonstrate that plant cover provides prey animals with refuges to decrease vulnerability to predators. However, others suggest plant cover to visually obstruct detection of predators or conspecifics. We suggest these seemingly conflicting results can, to some extent, be resolved if overhead vs. lateral cover are distinguished. We recorded seasonal variation in vigilance activity of a natural population of degus (Octodon degus), a diurnal, semi‐subterranean and social rodent from central Chile. We used these data to determine whether cover provided by herbaceous vegetation is mostly obstructive. The height of herbaceous vegetation in the habitat of degus varied seasonally, and the ability of degus (estimated from human observers) to detect potential predators decreased when herbaceous vegetation was high. This effect was more important for degus using quadruped postures and when dealing with terrestrial simulated predators. Accordingly, degus adjusted the quality rather than the quantity of their vigilance activity: male and female degus allocated similarly more time to bipedal vigilance when the height of herbs was high. Such increase in bipedal vigilance seemed to occur at the expense of quadruped vigilance instead of foraging time. Collectively, these results support the hypothesis that cover of herbaceous vegetation is mostly obstructive to degus when active above ground, a finding that contrasts with previous evidence supporting that shrub cover provides refuges against predators. The differential effects of shrubs and herbs on degu vigilance are likely linked to differences in the costs and benefits associated with each cover type. For degus, shrubs may provide more overhead (protective) than lateral (obstructive) cover.     

集群数量和采食距离对储草期布氏田鼠警戒频次的影响

警戒行为是动物对环境中潜在危险做出的反应。为探究影响警戒行为的因素,作者在内蒙古锡林郭勒典型草原区进行了集群数量和采食距离对储草期自由生活状态下布氏田鼠(Lasiopodomys brandtii)警戒频次影响的实验。通过标志重捕法和人工去除法设定3个集群数量梯度(11只、6只和3只),利用人工食物站设置4个采食距离梯度(5 m、10 m、20 m、30 m),共12个梯度组合,每个组合分别观察60次采食过程,共计观察720次,并记录采食过程中的警戒频次。对数据进行双因素方差分析,集群规模和采食距离对布氏田鼠警戒行为频次均有极显著影响(P0.01)。随着集群数量减小,布氏田鼠单次采食的警戒频次显著增加;采食距离越远,单次采食的警戒频次越高;集群数量和采食距离之间还存在极显著的交互作用(P0.01)。集群数量增大意味着采食距离的增加,为保证储草效率,布氏田鼠种群会在增加集群数量和减小采食距离之间权衡,最终集群数量维持在中等水平,支持了最优集群理论。     

Sexual,Seasonal and Group Size Differences in the Allocation of Time between Vigilance and Feeding in the Greater Rhea,Rhea americana

We studied the effect of sex and group size on the proportion of time a greater rhea, Rhea americana, allocates to vigilance and feeding during the breeding and the non-breeding seasons. We analysed 175 records of focal animals that were feeding alone or in groups of 2 to 26 birds. In both seasons, males spent more time in vigilance and less time in feeding than females. Both sexes spent more time in vigilance and less time in feeding during the breeding season. Sexual and seasonal differences in vigilance were the result of different mechanisms. Males had shorter feeding bouts than females but there were no sexual differences in the length of the vigilance bouts. On the contrary, seasonal differences were the result of males and females having longer vigilance bouts during the breeding season but there were no seasonal differences in the length of the feeding bouts. During the non-breeding season, individual vigilance was higher in rheas foraging alone than in groups. In this case, solitary birds had longer vigilance and shorter feeding bouts than birds foraging in groups. We discuss the possible effect of intragroup competition and food availability on the allocation of time between feeding and vigilance in this species.     

群体规模对越冬灰鹤警戒行为的影响

2005年1—3月,在云南丽江拉市海就群体规模对越冬灰鹤(Grusgrus)警戒行为的影响进行了研究。用扫描取样记录群体的规模和警戒个体的数量、用焦点取样记录群体中个体警戒行为的频次和持续时间,结果显示灰鹤群体和个体的警戒力均随群体规模增加而降低,但集群个体数超过30只后,群体警戒力便不会再下降(P>0.05)、成体的警戒持续时间也会增加(P<0.01);当群体规模超过50只后,成体的警戒频次也会上升(P<0.05)。推测亚成体维持低警戒的群体规模上限值要高于成体,单从警戒行为分析,20—30只个体的集群可能代表越冬灰鹤的最适群体大小。     

The Relationship between Regular Sports Participation and Vigilance in Male and Female Adolescents

The present study investigated the relationship between regular sport participation (soccer) and vigilance performance. Two groups of male and female adolescents differentiated in terms of their sport participation (athletes, n = 39, and non-athletes, n = 36) took part in the study. In one session, participants performed the Leger Multi-stage fitness test to estimate their aerobic fitness level. In the other session, participants completed the Psychomotor Vigilance Task (PVT) to evaluate their vigilance performance. Perceived arousal prior to the task and motivation toward the task were also measured in the PVT session. The results revealed that athletes had better cardiovascular fitness and showed better performance in the PVT. However, correlation analyses did not show any significant relationship between cardiovascular fitness and performance in the PVT. Athletes showed larger scores in motivation and perceived arousal measures with respect to non-athletes, although, once again, these variables were not correlated with PVT performance. Gender differences were observed only in the Leger test, with males showing greater fitness level than females. The major outcome of this research points to a positive relationship between regular sport participation and vigilance during adolescence. This relationship did not seem to be influenced by gender, perceived arousal, motivation toward the task or cardiovascular fitness. We discuss our results in terms of the different hypotheses put forward in the literature to explain the relationship between physical activity and cognitive functioning.     

相关风险因子对高原鼠兔摄食行为的影响

研究了捕食风险环境中集和洞口距离对高原鼠兔摄食行为的影响。结果表明,集群数量的增加不仅降低了警觉行为,同时也减少了摄食行为,在高风险环境中,集群为1时的取食行为强度最大,低风险环境中,为0时最大,警觉行为主要出现在距洞口2m的范围内,其行为强度与洞口踪影职责负相关,当洞口距离大于3m时,风险处理区的高原鼠兔几乎无警觉行为出现,且该处理区的取食区域几乎压缩的洞口旁,研究结果表明,在捕食风险环境中,高原鼠兔摄食行为与集群和洞口距离之间具有复杂的关系,其行为决策反映了降低风险与摄取食物间的权衡,行为目标是在降低捕食风险的同时尽可能地取食食物。     

Human Activity Dampens the Benefits of Group Size on Vigilance in Khulan (Equus hemionus) in Western China

Animals receive anti-predator benefits from social behavior. As part of a group, individuals spend less time being vigilant, and vigilance decreases with increasing group size. This phenomenon, called “the many-eyes effect”, together with the “encounter dilution effect”, is considered among the most important factors determining individual vigilance behavior. However, in addition to group size, other social and environmental factors also influence the degree of vigilance, including disturbance from human activities. In our study, we examined vigilance behavior of Khulans (Equus hemionus) in the Xinjiang Province in western China to test whether and how human disturbance and group size affect vigilance. According to our results, Khulan showed a negative correlation between group size and the percentage time spent vigilant, although this negative correlation depended on the groups’ disturbance level. Khulan in the more disturbed area had a dampened benefit from increases in group size, compared to those in the undisturbed core areas. Provision of continuous areas of high-quality habitat for Khulans will allow them to form larger undisturbed aggregations and to gain foraging benefits through reduced individual vigilance, as well as anti-predator benefits through increased probability of predator detection.     

Load Size Variation in the Eastern Chipmunk,Tamias striatus: The Importance of Distance from Burrow and Canopy Cover

We examined the degree to which chipmunks foraging from dishes containing sunflower seeds varied cheek pouch load size according to both travel time (distance from burrows) and predation hazard (canopy cover). Results showed that larger loads were taken under cover at some distance from burrows than were taken from closer or more open sites. Distance effects appeared to reflect the influence of traveling times on quitting harvest rates as predicted by central place foraging models. Quitting harvest rates also appeared to be higher under low than under dense canopy cover; this trend was most pronounced at some distance from burrows suggesting that foraging decisions were made relative to both energetics and predator avoidance. Chipmunks appeared to employ a patch exploitation strategy that minimized the hazard:gain ratio.     

The Long and the Short of It: No Dietary Specialisation between Male and Female Western Sandpipers Despite Strong Bill Size Dimorphism

Many bird species show spatial or habitat segregation of the sexes during the non-breeding season. One potential ecological explanation is that differences in bill morphology favour foraging niche specialisation and segregation. Western sandpipers Calidris mauri have pronounced bill size dimorphism, with female bills averaging 15% longer than those of males. The sexes differ in foraging behaviour and exhibit partial latitudinal segregation during the non-breeding season, with males predominant in the north and females in the south. Niche specialisation at a local scale might account for this broad geographic pattern, and we investigated whether longer-billed females and shorter-billed males occupy different foraging niches at 16 sites across the non-breeding range. We used stable-nitrogen (δ¹⁵N) isotope analysis of whole blood to test for dietary specialisation according to bill length and sex. Stable-nitrogen isotope ratios increase with trophic level. We predicted that δ¹⁵N values would increase with bill length and would be higher for females, which use a greater proportion of foraging behaviour that targets higher-trophic level prey. We used stable-carbon (δ¹³C) isotope analysis to test for habitat segregation according to bill length and sex. Stable-carbon isotope ratios vary between marine- and freshwater-influenced habitats. We predicted that δ¹³C values would differ between males and females if the sexes segregate between habitat types. Using a model selection approach, we found little support for a relationship between δ¹⁵N and either bill length or sex. There was some indication, however, that more marine δ¹³C values occur with shorter bill lengths. Our findings provide little evidence that male and female western sandpipers exhibit dietary specialisation as a function of their bill size, but indicate that the sexes may segregate in different habitats according to bill length at some non-breeding sites. Potential ecological factors underlying habitat segregation between sexes include differences in preferred habitat type and predation risk.     

Relationship between Endopolyploidy and Cell Size in Epidermal Tissue of Arabidopsis

Relative quantities of DNA in individual nuclei of stem and leaf epidermal cells of Arabidopsis were measured microspectrofluorometrically using epidermal peels. The relative ploidy level in each nucleus was assessed by comparison to root tip mitotic nuclei. A clear pattern of regular endopolyploidy is evident in epidermal cells. Guard cell nuclei contain levels of DNA comparable to dividing root cells, the 2C level (i.e., one unreplicated copy of the nuclear DNA). Leaf trichome nuclei had elevated ploidy levels of 4C, 8C, 16C, 32C, and 64C, and their cytology suggested that the polyploidy represents a form of polyteny. The nuclei of epidermal pavement cells were 2C, 4C, and 8C in stem epidermis, and 2C, 4C, 8C, and 16C in leaf epidermis. Morphometry of epidermal pavement cells revealed a direct proportionality between nuclear DNA level and cell size. A consideration of the development process suggests that the cells of highest ploidy level are developmentally oldest; consequently, the developmental pattern of epidermal tissues can be read from the ploidy pattern of the cells. This observation is relevant to theories of stomate spacing and offers opportunities for genetic analysis of the endopolyploidy/polyteny phenomenon.     

Flight Distance and Eye Size in Birds

Larger eyes capture more information from the environment than small eyes, but also require more brain space for information processing. Therefore, individuals have to optimize the size of their eyes, leading to the prediction that larger eyes should have evolved in species with greater benefits from large eyes, such as species subject to intense predation risk. In a comparative analysis of 97 bird species, we found that species that fled at longer distances from an approaching potential predator indeed had relatively large eyes for their body size. In contrast, there was no indication that large eyes had evolved in species living in secluded habitats, or in species eating mobile prey. These findings are consistent with the assumption that eye size is labile and can evolve in response to changing predator environments. They also suggest that eye size may act as a constraint on optimal anti‐predator behavior, if the predator community changes as a consequence of introductions or invasions.     

Scaling of Pelagic Metabolism to Size,Trophy and Forest Cover in Small Danish Lakes

ABSTRACT We tested whether pelagic light and nutrient availability, metabolism, organic pools and CO₂-supersaturation were related to lake size and surrounding forest cover in late summer–autumn measurements among 64 small (0.02–20 ha), shallow seepage lakes located in nutrient-rich, calcareous moraine soils in North Zealand, Denmark. We found a strong implicit scaling to lake size as light availability increased significantly with lake size while nutrient availability, phytoplankton biomass and dissolved organic matter declined. Forest lakes had significantly stronger net heterotrophic traits than open lakes as higher values were observed for light attenuation above and in the water, dissolved organic matter, pelagic community respiration (R) relative to maximum gross primary production (R/GPP) and CO₂-supersaturation. Total-phosphorus was the main predictor of phytoplankton biomass (Chl) despite a much weaker relationship than observed in previous studies of larger lakes. Maximum gross primary production increased with algal biomass and decreased with dissolved organic matter, whereas community respiration increased with dissolved organic matter and particularly with gross primary production. These results suggest that exogenous organic matter supplements primary production as an energy source to heterotrophs in these small lakes, and particularly so in forest lakes experiencing substantial shading from the forest and dissolved humic material. This suggestion is supported by 20–30-fold CO₂ supersaturation in the surface water of the smallest forest lakes and more than sixfold supersaturation in 75% of all measurements making these lakes among the most supersaturated temperate lakes examined so far.     

Neocortex Size Predicts Group Size in Carnivores and Some Insectivores

Neocortex size has been shown to correlate with group size in primates. Data for carnivores and insectivores are used to test the generality of this relationship. The data suggest that carnivores lie on the same grade as the primates, but that insectivores lie on a separate grade to the left of these two orders. Among the insectivores, there appears to be a distinction between the ‘advanced’ genera (which show a relationship between group size and neocortex size) and the ‘basal’ genera (which do not).     

Multilevel Selection 4: Modeling the Relationship of Indirect Genetic Effects and Group Size

Indirect genetic effects (IGE) occur when individual trait values depend on genes in others. With IGEs, heritable variance and response to selection depend on the relationship of IGEs and group size. Here I propose a model for this relationship, which can be implemented in standard restricted maximum likelihood software.SOCIAL interactions among individuals are abundant in life (Frank 2007). Trait values of individuals may, therefore, depend on genes in other individuals, a phenomenon known as indirect genetic effects (IGE; Wolf et al. 1998) or associative effects (Griffing 1967; Muir 2005). IGEs may have drastic effects on the rate and direction of response to selection. Moreover, with IGEs, heritable variance and response to selection depend on the size of the interaction group, hereafter denoted group size (Griffing 1967; Bijma et al. 2007; McGlothlin et al. 2010). The magnitude of the IGEs themselves, however, may also depend on group size, because interactions between a specific pair of individuals are probably less intense in larger groups (Arango et al. 2005). The relationship between the magnitude of IGEs and group size is relevant because it affects the dynamics of response to selection, heritable variation, and group size, determining, e.g., whether or not selection is more effective with larger groups. Moreover, a model for this relationship is required to estimate IGEs from data containing varying group sizes. Hadfield and Wilson (2007) proposed a model for the relationship between IGEs and group size. Here I present an alternative.With IGEs, the trait value of focal individual i is the sum of a direct effect rooted in the focal individual itself, P_D,i, and the sum of the indirect effects, P_S,j, of each of its n − 1 group mates j,(1)where A and E represent the heritable and nonheritable component of the full direct and indirect effect, respectively, and n denotes group size (Griffing 1967). When IGEs are independent of group size, total heritable variance in the trait equals (Bijma et al. 2007)(2)For a fixed becomes very large with large groups. This is unrealistic because an individual''s IGE on a single recipient probably becomes smaller in larger groups. The decrease of IGEs with group size, referred to as dilution here, will depend on the trait of interest. With competition for a finite amount of feed per group, for example, an individual consuming 1 kg has an average indirect effect of P_S,i = −1/(n − 1) on feed intake of each of its group mates. Hence, the indirect effect is inversely proportional to the number of group mates, indicating full dilution. The other extreme of no dilution may be illustrated by alarm-calling behavior, where an individual may warn all its group mates when a predator appears, irrespective of group size. Here the indirect effect each group mate receives is independent of group size, indicating no dilution. The degree of dilution is an empirical issue, which may be trait and population specific, and needs to be estimated.Here I propose to model dilution of indirect effects as(3)where P_S,i,n is the indirect effect of individual i in a group of n members, P_S,i,2 the indirect effect of i in a group of two members, and d the degree of dilution. With no dilution, d = 0, indirect effects do not depend on group size, P_S,i,n = P_S,i,2, as with alarm-calling behavior. With full dilution, d = 1, indirect effects are inversely proportional to the number of group mates, P_S,i,n = P_S,i,2/(n − 1), as with competition for a finite amount of feed. Equation 3 is an extension of the model of Arango et al. (2005), who used d = 1.Assuming that IGEs are diluted in the same manner as the full indirect effect, the indirect genetic variance for groups of n members equals(4)and total heritable variance equals(5)Hence, for σ_ADS = 0, total heritable variance increases with group size as long as dilution is incomplete (d < 1). Total heritable variance is independent of group size with full dilution (d = 1). Phenotypic variance also depends on group size. With unrelated group members,(6)which increases with group size for d < 0.5, is independent of group size for d = 0.5, and decreases with group size for d > 0.5.The degree of dilution can be estimated from data containing variation in group size, by using a mixed model with restricted maximum likelihood and evaluating the likelihood for different fixed values of d (Arango et al. 2005; Canario et al. 2010). With Equation 3, however, the estimated genetic (co)variances and breeding values for indirect effect refer to a group size of two individuals, which is inconvenient when actual group size differs considerably. Estimates of A_S, , and σ_ADS referring to the average group size may be obtained from the following mixed model,(7)where z is a vector of observations, Xb are the usual fixed effects, Z_Da_D are the direct genetic effects, Z_gg are random group effects, and e is a vector of residuals. The is a vector of IGEs referring to the average group size, and Z_S(d) is the incidence matrix for IGEs, which depends on the degree of dilution; dilution being specified relative to the average group size. Elements of Z_S(d) are(8)where denotes average group size. This model is equivalent to Equation 3, but yields estimates of genetic parameters and breeding values referring to the average group size because for . When the magnitude of IGEs depends on group size, the group and residual variance in Equation 7 will depend on group size:(9a)(9b)Hence, to obtain unbiased estimates of the genetic parameters and d, it may be required to fit a separate group and residual variance for each group size.To account for the relationship between IGEs and group size, Hadfield and Wilson (2007; HW07) proposed including an additional IGE. In their model, an individual''s full IGE is the sum of an effect independent of group size, and an effect regressed by the reciprocal of the number of group mates,(10)There are a number of differences between both models. First, Equation 3 specifies the relationship between the magnitude of IGEs and group size on the population level, which is sufficient to remedy the problem of increasing variance with group size. The HW07 model, in contrast, specifies the relationship between the magnitude of IGEs and group size on the individual level. In the HW07 model, the absolute value of (1/(n − 1))A_SR,_i decreases with group size, while A_S,i is constant. Consequently, the relationship between an individual''s full IGE and group size depends on the relative magnitudes of its A_S,i and A_SR,_i; the IGEs of individuals with greater |A_SR| show greater change when group size varies. This alters the IGE ranking of individuals when group size varies. The HW07 model, therefore, not only scales IGEs with group size, but also allows for IGE-by-group-size interaction, whereas Equation 3 scales IGEs of all individuals in the same way. Second, the interpretation of the genetic parameters differs between both models. In the HW07 model, lim_n→∞ A_S,i,HW07 = A_S,i, meaning that Var(A_S) represents the variance in IGEs when group size is infinite. With Equation 3 or 7, in contrast, refers to groups of two individuals or to the average group size. Third, in the HW07 model, the dilution of IGEs with group size is implicitly incorporated in the magnitudes of Var(A_S) and Var(A_SR), greater Var(A_SR) implying greater dilution. Equation 3, in contrast, has a single parameter for the degree of dilution, expressed on a 0–1 scale. Finally, implementing the HW07 model involves estimating three additional covariance parameters, Var(A_SR), Cov(A_D, A_SR), and Cov(A_S, A_SR), whereas implementing the model proposed here involves estimating a single additional fixed effect, which is simpler. In conclusion, the HW07 model has greater flexibility than the model proposed here, but is also more difficult to implement and interpret.