Kokko H, Johnstone R A, Clutton-Brock T H
Department of Zoology, University of Cambridge, UK.
Proc Biol Sci. 2001 Jan 22;268(1463):187-96. doi: 10.1098/rspb.2000.1349.
Some individuals (helpers) in cooperatively breeding species provide alloparental care and often suppress their own reproduction. Kin selection is clearly an important explanation for such behaviour, but a possible alternative is group augmentation where individuals survive or reproduce better in large groups and where it therefore pays to recruit new members to the group. The evolutionary stability of group augmentation is currently disputed. We model evolutionarily stable helping strategies by following the dynamics of social groups with varying degrees of subordinate help. We also distinguish between passive augmentation, where a group member benefits from the mere presence of others, and active augmentation, where their presence as such is neutral or harmful, but where helping to recruit new group members may still be beneficial if they in turn actively provide help for the current reproductives ('delayed reciprocity'). The results show that group augmentation (either passive or active) can be evolutionarily stable and explain costly helping by non-reproductive subordinates, either alone or leading to elevated help levels when acting in concert with kin selection. Group augmentation can thus potentially explain the weak relationships between relatedness and helping behaviour that are observed in some cooperatively breeding species. In some cases, the superior mutualistic performance of cooperatively behaving groups can generate an incentive to stay and help which is strong enough to make ecological constraints unnecessary for explaining the stability of cooperatively breeding groups.
在合作繁殖物种中，一些个体（帮助者）提供异亲抚育，并且常常抑制自身的繁殖。亲缘选择显然是对这种行为的一个重要解释，但另一种可能的解释是群体扩充，即个体在大群体中生存或繁殖得更好，因此招募新成员加入群体是有利可图的。目前，群体扩充的进化稳定性存在争议。我们通过追踪具有不同程度从属帮助的社会群体的动态，来模拟进化稳定的帮助策略。我们还区分了被动扩充（即群体成员仅仅从其他成员的存在中受益）和主动扩充（即其他成员的存在本身是中性的或有害的，但如果帮助招募新群体成员，而这些新成员反过来又积极为当前繁殖者提供帮助（“延迟互惠”），那么这仍然可能是有益的）。结果表明，群体扩充（被动或主动）可以是进化稳定的，并且可以解释非繁殖性从属者付出代价的帮助行为，这种行为单独存在时或者与亲缘选择共同作用导致帮助水平提高时都能解释。因此，群体扩充有可能解释在一些合作繁殖物种中观察到的亲缘关系与帮助行为之间的微弱关系。在某些情况下，合作行为群体的卓越互利表现能够产生一种留下来提供帮助的动机，这种动机足够强烈，以至于无需用生态限制来解释合作繁殖群体的稳定性。
