環境和社會因子對冠羽畫眉繁殖權利分享之影響

Abstract

社會性動物會彼此合作獲取共同利益，但群成員間亦需競爭這些共有的利益。繁殖對動物來說是最直接也是最主要的利益之一，瞭解合作群體內的繁殖偏差(reproductive skew)和其影響因子，就能夠知道動物如何分配利益以維持穩定的合作關係。現今繁殖偏差的議題已經吸引了許多理論的注意，像是交易模型、角力競爭模型、子代成本模型，但是實驗性的研究多著重於理論預測的驗證和高位階完全控制次位階的繁殖假設，關於環境因子對繁殖分配的影響，和衝突解決機制的檢測則相對稀少─尤其是非親緣的合作群體。冠羽畫眉(Yuhina brunneiceps)為多對非親緣個體共用一巢的合作生殖系統，藉由觀察其繁殖行為，搭配氣候資料，正適合來驗證繁殖偏差理論與其衝突解決機制。本研究分析2001-2007年繁殖季期間各繁殖群的子代數量、子代品質，和環境狀況。結果發現，當產蛋前的雨量小(環境好)，或打鬥時間較長時，高位階個體的子代較重，而次位階個體有較多的子代數。在雨量大(環境差)時，打鬥行為少，高位階個體有較重且較多的子代。結果顯示，環境好時繁殖利益分配符合角力競爭模型(tug-of-war model)，環境差時則由子代成本模型(costly young model)影響繁殖分配。透過冠羽畫眉繁殖偏差的研究，我發現生態環境會影響衝突解決機制，瞭解不同環境下的衝突解決機制，能夠讓我對合作群體中面對利益分配和衝突時，如何維持穩定的合作關係有更好的理解。

Animals form groups, they cooperate and compete with their group members. One of the most important benefits in group living is reproduction. Knowing the reproductive skew in group is the key to reveal the secret of maintained cooperation. Studies of reproductive skew already get many attentions from theoretical research. However, most of empirical studies focus on the test of predictions and the assumption of reproduction complete control from dominant, the effect of ecological factors and the test of conflict resolution mechanism is rare – especially in non-kin species. Taiwan yuhina (Yuhina brunneiceps) has a joint-nesting breeding system in which several genetic unrelated pairs breed in a single nest. By observed their reproduction behavior and environment, is especially suited for the test of reproductive skew and the relationship between ecological conditions and conflict resolution mechanism. This study recorded total 52 breeding groups’ nestling number, nestling weight and ecological factors in every breeding season from 2001 to 2007. Result shows that dominant’s offspring was heavier but less than subordinate when precipitation was low (favourable ecological condition) or tussling time was longer. Dominant take advantaged in both nestling number and weight when precipitation was high, as well as tussling was rare happened. These results were predicted by the tug-of-war model in favourable ecological condition and costly young model in unfavourable ecological condition. Our study indicates that different conflict resolution mechanism was worked under different ecological conditions. By knowing the effect of ecological condition among conflict resolution mechanism, we can have a better understanding of cooperation maintains when conflict occur.