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1.
We determined how the presence of heterospecific individuals in the vicinity of a focal individual affects the behavior of two critically endangered species of cranes on their wintering grounds at Cheolwon in the Korean Demilitarized Zone. The red-crowned crane, Grus japonensis, is larger than the white-naped crane, Grus vipio, and it dominates the white-naped crane in aggressive interactions. We showed that the dominant species increases foraging activity in the presence of the subordinate species presumably because of scrounging of food from the subordinate. Because interspecific interactions may affect avian endangerments these behavioral findings should be taken into account when managing winter refuges for the two endangered crane species.  相似文献   

2.
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。  相似文献   

3.
Vigilance achieved at the group level, known as collective vigilance, can enhance the ability to assess threats and confer benefits to gregarious prey species. Examining the factors that influence collective vigilance and exploring how individual vigilance is organized at the group level can help to understand how prey groups respond to potential threats. We quantified collective vigilance and determined its temporal pattern in a natural wintering population of the hooded crane Grus monacha in the Shengjin Lake reserve in China. We examined the role of flock size and anthropogenic disturbances in the human‐dominated landscape on collective vigilance and level of synchronization. The proportion of time during which at least one individual scanned the surroundings (collective vigilance) increased with flock size and was higher in the more disturbed buffer zone of the lake. Synchronization of vigilance occurred more frequently in the smaller flocks but was not related to the risk of disturbance. Synchronization implies that individuals tend to monitor and copy the vigilance of neighbors. In the degraded wetlands, the wintering hooded crane benefits from foraging in groups and synchronizing their vigilance in response to human disturbances.  相似文献   

4.
Prey can obtain valuable benefits from associating with other species if heterospecifics help to detect predators or locate good food patches. In mixed‐species groups, how species respond to the presence of other species remains a poorly explored question although it might give crucial insights into mechanisms underlying the interspecific coexistence. We studied temporary mixed‐species groups of large herbivores in Hwange National Park (Zimbabwe) between the common impala (Aepyceros melampus), the focal species here, and bigger species including the plains zebra (Equus quagga), the greater kudu (Tragelaphus strepsiceros) or the blue wildebeest (Connochaetes taurinus). In the Hwange savanna, the focal and smaller species are exposed to a larger range of predators than the associated species. In this context, we investigated how impalas adjusted their vigilance with group size comparing impala‐only and mixed‐species groups and whether the identity of heterospecifics affected vigilance of impalas. Our study showed that the time impalas spent in vigilance significantly decreased with group size when they formed impala‐only groups, whereas it did not significantly vary with group size in mixed‐species groups. Moreover, in mixed‐species groups, impalas did not adjust their time spent in vigilance with the proportion of conspecifics and the identity of the associated species. Thus, the mechanism underlying the difference of impalas' behavioural adjustment of vigilance with group size between single‐ and mixed‐species groups seemed to be related to the presence but not to the number and the identity of heteropecifics. Finally, we discuss the concept that larger and dominant heterospecifics were likely to increase competition for food access, thereby forcing higher vigilance of impalas, outweighing any reduction from collective vigilance.  相似文献   

5.
车烨  杨乐  李忠秋 《生态学报》2018,38(4):1375-1381
以往关于动物警戒行为的研究多以经典随机独立模型为基础,然而,近期一些理论和实证研究则向该模型发出了挑战。根据警戒行为同步性程度的不同,集体警戒可能存在基于模仿的同步警戒和避免重复的协调警戒两种模式。研究了中国雅鲁藏布江自然保护区越冬黑颈鹤家庭群的警戒行为,通过独立样本t检验验证由于年龄和是否携幼所导致的个体警戒水平的差异,通过单因素方差分析比较不同类型家庭群的集体警戒水平,通过配对t检验比较集体警戒的实际观测值和独立假设下的预期值从而确定越冬黑颈鹤家庭群的警戒同步性。结果表明家庭群中的幼年黑颈鹤警戒行为时间显著低于成年黑颈鹤,但幼鹤的存在对成鹤的警戒水平没有显著影响。不同类型黑颈鹤家庭群的集体警戒水平没有差异,但并未如预期表现为同步警戒。警戒行为模式是动物在特定环境中的适应性表现,越冬黑颈鹤生境中不存在落后目标策略的捕食者和高强度的捕食风险,因而可能不足以诱发以降低捕食风险为主要功能的高强度的警戒行为同步性;同时,在资源匮乏的冬季对食物获取的优先性可能也削弱了对同步警戒的需求。  相似文献   

6.
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   

7.
Animals often spend less time vigilant and more time feeding when foraging in larger groups. This group-size effect does not, however, consider if larger groups differ systematically from smaller ones: Large groups could form in different habitats than small groups or be composed of a different mix of ages or classes than small groups. We examined how habitat differences and flock size and composition explain feeding and vigilance rates in common cranes Grus grus , wintering in holm oak Quercus ilex dehesas of Spain. Flock size and composition were related to habitat type in cranes: flocks formed in areas sown with cereal crops were larger than flocks formed in set aside areas. Vigilance rate depended on habitat but decreased with increasing flock size in a similar way across all habitats. Juveniles were less vigilant than adults and showed little change in vigilance with flock size. Vigilance increased and feeding time decreased over months from November through February. Our results show that vigilance is affected by habitat but that the group size effect on vigilance is not the product of differences between habitats in group size or composition.  相似文献   

8.
Abstract Improved predator detection is often stated to be one of the principal benefits of social foraging. However, actual field evidence supporting this assumption is scarce. This may be the result of the fact that most observations are conducted on social animals acting in the absence of an acute predation threat, yet the benefits of grouping come to the fore in that brief moment when an individual's life is at risk. As predation attempts are typically rare in nature, experimental manipulations are necessary to further explore the costs and benefits of social foraging. This study utilizes simple predator simulations (by humans) to experimentally test the predator‐detecting abilities and escape strategies of groups of free‐living emus Dromaius novaehollandiae. Emus in larger groups spent less time in vigilance and more time foraging. Nonetheless, the combined vigilance of group members ensured that emus detected the ‘simulated predator’ sooner as group size increased. After detecting the ‘predator’, larger groups waited longer until opting to flee, and then spent less time and energy doing so. Thus, the results of this study provide experimental evidence that emus benefit from grouping in terms of both the ‘many‐eyes effect’ and the ‘dilution effect’.  相似文献   

9.
Grouping behavior of social ungulates may depend on both predator occurrence and perceived predation risk associated with habitat structure, reproductive state, and density of conspecifics. Over 3 years, we studied grouping behavior of guanaco (Lama guanicoe) families in Chilean Patagonia during the birthing season and determined their response to variation in predator occurrence and perceived predation risk (habitat structure, calf/adult rate, and density of conspecifics). We considered the effect of two predators, puma (Puma concolor) and culpeo fox (Lycalopex culpaeus). We measured two common (family group size and vigilance) and one novel (family group cohesion) behavioral responses of guanaco. Our results show that guanaco family groups adapted their grouping behavior to both predator occurrence and perceived predation risk. Larger family groups were found in open habitats and areas with high puma occurrence, while guanacos stayed in small family groups in areas with high shrub cover or low visibility. Group cohesion increased in areas with higher occurrence of pumas and culpeo foxes, and also increased in smaller family groups and in areas with low guanaco density. Vigilance (number of vigilant adults) was mainly related to group size and visibility, increasing in areas with low visibility, while residual vigilance (vigilance after removing the group‐size effect) did not vary with the explanatory variables examined. Our results suggest that a mix of predator occurrence and perceived predation risk influences guanaco grouping behavior and highlights the importance of evaluating different antipredator responses together and considering all predator species in studies aimed at understanding ungulate behavior.  相似文献   

10.
Previous work on mammals and birds has often demonstrated a negative relationship between group size and individual vigilance. However, this relationship has received only weak support in nonhuman primates. This result may be due to the failure to distinguish different forms of vigilance such as antipredatory vigilance and social monitoring. Here, we tested the effects of group size, reproductive status (breeding vs. nonbreeding), and sex on antipredatory vigilance and social monitoring in captive common marmosets (Callithrix jacchus). Behavioral observations using one-zero sampling were conducted on adult members of three captive groups of small, medium, and large size. Data were analyzed using a series of general linear models (GLMs) analyses of covariance (ANCOVAs). We found an overall negative group size effect on antipredatory vigilance and that breeders, especially breeding males, were significantly more vigilant than nonbreeders. Conversely, we found that social monitoring increased with group size. Unlike the results for antipredatory vigilance, neither breeders and nonbreeders nor males and females differed in their amounts of social monitoring. However, the effect of group size appeared to differ for nonbreeding males compared to all other adults. Our results generally support the idea that individuals in larger groups are safer with breeding males likely playing a prominent role in protection from predation. The increase in social monitoring may be related to increased reproductive competition with the presence of adult offspring, but future studies need to clarify the target of social monitoring in both breeders and nonbreeders. Overall, the study underlines the importance of distinguishing different forms of vigilance and other factors as they may confound the effects of group size on antipredatory vigilance.  相似文献   

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