越冬白额雁警戒行为的群体效应和对策选择机制

Since being proposed, group size effect has been verified in a variety of mammals, birds, reptiles, and other animal categories. However, nearly a third of studies did not found the negative relationship between group size and vigilance level predicted by group size effect. In recent years, ethologists verified that vigilance was not only directed to predators (antipredator vigilance), but also directed to conspecifics (conspecific vigilance). They further proposed that conspecific vigilance should increase as group size increase, and antipredator vigilance should decrease as group size increase. Proportions of these two vigilance categories (conspecific vigilance and antipredator vigilance) changed in different species and different populations of the same species, which incurred the contradictory results found above. Distinguishing and quantifying proportions of antipredator vigilance and conspecific vigilance were prerequisite for verifying their newly proposed hypothesis. However, studies on this aspect were extremely scarce, expect for one study conducted on group living eastern grey kangaroos. In this project, we will distinguish and quantify the relative proportions of conspecific vigilance and antipredator vigilance of individuals from wintering greater white-fronted goose foraging groups. Then we will test the effects of group size, number of nearby neighbors, individual position within a group, and competition intensity on levels of conspecific vigilance and antipredator vigilance. Furthermore, we will re-examine group size effect and edge effect with levels of conspecific vigilance and antipredator vigilance as dependent variables. Finally, we will try to uncover the adaptive vigilance strategies of individual greater white-fronted goose in the frequently changed groups during wintering seasons. The conducting of this project will provide new approaches for studies on vigilance theories of aggregational animals and optimal group size formation theories.

警戒行为的群体效应在许多动物类群中获得了广泛的验证，然而，有近三分之一的研究结果不符合群体效应的预测。近年来，行为学家证实除了监视捕食者（捕食者警戒）外，部分警戒行为的目的是监视群体内其它成员（同类警戒）。同类警戒水平可能随着群体增大而上升，从而导致一些研究发现总警戒水平不随群体增大而降低（不符合群体效应预测）。区分和定量同类警戒和捕食者警戒水平是验证这一假设的前提，对于警戒理论的发展有重要意义，而这方面的研究工作极为匮乏。本项目拟以越冬白额雁为研究对象，区分和定量同类警戒和捕食者警戒水平；探索群体大小、邻近个体数量、个体在群体中的位置、竞争强度等因素对同类警戒水平以及捕食者警戒水平的影响；从新的角度重新验证群体效应、边缘效应等经典假说；揭示越冬白额雁警戒策略随群体变化的适应机制。本项目的开展将为集群动物警戒理论和最优群体大小形成理论的研究提供新的思路。

本项目以专性取食苔草的越冬白额雁觅食群为研究对象，观察和记录白额雁个体警戒行为和觅食行为，利用广义线性混合模型、局部加权回归和分段回归等分析方法，探讨了白额雁个体警戒策略选择和觅食效率随群体大小、邻近个体数量和群体位置等因子变化的规律。主要研究结果包括：1）白额雁个体的警戒频率、警戒平均持续时间和警戒时间占比与群体大小关系不显著，随邻近其它同种个体的数量增加而上升，处于群体边缘的个体警戒水平显著高于中间个体，中间个体的警戒水平与邻近个体数量的关系比边缘个体更显著；2）目标个体的觅食时间、觅食效率和觅食率与群体大小无关、随邻近个体数量增加而降低，边缘个体比中间个体具有更高的觅食收益；3）邻近个体数量越多，个体之间的竞争强度越大；而在没有明显打斗等竞争行为的情形下，目标个体的警戒水平随邻近个体数量增加而上升，觅食收益随邻近个体数量增加而降低，显示隐形竞争的存在，证明了越冬白额雁觅食群中警戒行为的主要对象是邻近其它同类个体，即同类警戒水平高于捕食者警戒水平。4）针对现有研究中普遍采用主观定义个体在群体中的位置问题，采用距边缘距离的方法定量衡量个体在群体中的位置，利用局部加权回归和分段回归分析警戒投入和觅食收益与距边缘距离的关系，结果显示，白额雁觅食群边缘效应的范围为距边缘2.5米范围内，新方法定义的个体位置与传统方法相比具有更加显著的边缘效应。本项目的研究结果表明在类似于白额雁觅食群的大的动物集群中群体效应不明显，边缘效应仍然发挥作用，研究结果是对现有动物集群理论的部分验证、有益补充和进一步延申。此外，白额雁觅食群的形成不仅能够降低捕食风险，也可提高觅食效益。同类警戒和隐形竞争的广泛存在表明，越冬白额雁可能面临生境和食物资源短缺的问题。由于白额雁在长江中下游主要以苔草为食物，不利用农田生境，增加自然湿地面积和苔草资源量有助于缓解群体内部竞争压力，促进种群增长。