Department of Animal Behaviour, Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, Zurich 8057, Switzerland.
J Anim Ecol. 2012 May;81(3):649-56. doi: 10.1111/j.1365-2656.2011.01939.x. Epub 2012 Jan 4.
1. While the reasons for group-living have been studied for decades, little is known about why individuals become solitary. 2. Several previous experimental studies could demonstrate that group-living can arises as a consequence of ecological constraints. 3. It has been argued that reproductive competition between group members leads to significant costs of group-living, being a main reason of solitary-living. However, so far, no studies tested experimentally whether reproductive competition can explain solitary-living. 4. Using a socially flexible species, the African striped mouse (Rhabdomys pumilio), we tested experimentally in the field whether dispersal and solitary-living are more likely to occur when reproductive competition is present. 5. We investigated ecological constraints, here expressed as a function of population density, by removing groups of striped mice and creating vacant territories. To control for the effect of reproductive competition, which occurs only during the breeding season, we performed experiments during both the breeding and the non-breeding season. This is the first removal experiment performed in a species with communal breeding during the non-breeding season. 6. During the breeding season, when population density was low, more striped mice from experimental groups moved into the vacant territories and became solitary than striped mice from control groups. This is in support of the ecological constraints hypothesis. 7. During the non-breeding season, striped mice remained group-living despite the availability of free territories. Significantly, more striped mice became solitary-living during the breeding than during the non-breeding season. This is the first experimental support for the reproductive competition hypothesis explaining solitary-living. 8. Analysis of the sexual maturity of males showed that males which became solitary had a higher reproductive potential than males that remained group-living. Analysis of the body mass data of females showed that more solitary females reproduced than group-living females. These results indicate that by becoming solitary individuals of both sexes avoided costs of reproductive competition within groups. 9. Our study provides experimental evidence that reproductive competition within groups can lead to dispersal and solitary-living.
尽管群居的原因已经研究了几十年,但对于个体为何独居却知之甚少。
之前有几项实验研究表明,群居可以是生态约束的结果。
有人认为,群体成员之间的繁殖竞争会导致群居的巨大成本,这是独居的主要原因。然而,到目前为止,还没有研究通过实验来验证繁殖竞争是否可以解释独居现象。
我们使用一种具有社交灵活性的非洲条纹鼠(Rhabdomys pumilio),在野外进行了实验,以测试繁殖竞争存在时,扩散和独居是否更有可能发生。
我们通过去除条纹鼠群体并创造空旷领地来调查生态约束,这里的生态约束表现为种群密度的函数。为了控制繁殖竞争的影响,这种竞争只发生在繁殖季节,我们在繁殖和非繁殖季节都进行了实验。这是在非繁殖季节具有群居繁殖的物种中进行的第一次去除实验。
在繁殖季节,当种群密度较低时,来自实验组的更多条纹鼠会迁移到空旷的领地并变得独居,而对照组的条纹鼠则较少。这支持了生态约束假说。
在非繁殖季节,尽管有空置的领地,但条纹鼠仍保持群居。重要的是,繁殖季节比非繁殖季节有更多的条纹鼠变得独居。这是首次通过实验支持解释独居现象的繁殖竞争假说。
对雄性性成熟的分析表明,变得独居的雄性具有比保持群居的雄性更高的生殖潜力。对雌性体重数据的分析表明,独居的雌性比群居的雌性繁殖更多。这些结果表明,通过变得独居,雌雄个体都避免了群体内繁殖竞争的成本。
我们的研究提供了实验证据,表明群体内的繁殖竞争会导致扩散和独居。