鳥類的社會征服：全球鳥類社會性與分布範圍之探討

Abstract

具有合作生殖特徵的動物遍佈世界各地。先前的研究指出合作行為起源於良性且可預測的環境，但亦可能起源於惡劣且變動的環境中。雙重群體利益理論提到當鳥類的合作行為是源自於在良好及穩定環境時，其合作行為主要為了對抗個體數飽和的環境及種內競爭；然而，在嚴苛且變動的環境下，合作生殖的物種其合作行為將可以增加在惡劣環境中收集資源的效率以及增加育雛成功率。也就是說，不同生態原因以及合作利益將會導致不同合作類型，且個體從合作中所獲得的利益將影響生態後果(物種之地理分布範圍大小)。本篇研究將利用全球尺度的鳥類類群以及物種的分布範圍來檢驗雙重利益理論，我預測當合作行為在良好及穩定環境中演化出來時，因為個體數飽和的環境而使得個體傾向留在母群體當中，所以具合作生殖行為特徵的物種與不具合作生殖行為的物種之地理分布範圍不會有顯著差異。另一方面，在嚴苛且變動的環境下演化出的合作行為的物種將可以藉由合作來提高其在惡劣環境時的環境適存度，所以合作的物種將比非合作物種具有更大的地理分布範圍。本篇研究利用系統發育迴歸分析以及系統發育路徑分析來建構物種的生活史特徵(體重與社會系統)、氣候因子以及地理分布範圍之間的因果關係，並且表明合作生殖是一個包含雙重群體利益的概括性名詞，而物種的分布範圍則是區分兩種合作利益的關鍵因子。最後強調了如何區分形成合作團體的原因是釐清合作生殖行為演化的重要概念，為接下來的研究提供了有利的證據以及經驗範例。

Cooperative breeding animals are widely distributed over the world. Previous studies showed that cooperatively breeding behavior was derived from both benign and predictable, harsh and unpredictable environments. This fact can be illustrated by the dual-benefits framework. It mentions that there will be no significant differences in the geographical distribution between the cooperative and non-cooperative species when cooperative behavior derived from benign and stable environments, because individuals tend to stay in the natal group in saturated environments. On the other hand, cooperative breeding behavior derived from harsh and unpredictable environments will lead to a larger species range size because cooperative behavior will increase the fitness of cooperative species. In other words, different types of cooperation are formed by different ecological reasons and cooperative benefits, which will affect the ecological consequences (the geographical distribution of species). This study uses phylogenetic analyses and phylogenetic confirmatory path analysis to construct causal relationships between life-history traits (body mass and social system), climate factors, and geographical distribution by analyzing avian species range size in global scale. The results show that cooperative breeding behavior is an umbrella term, which including all social groups formed by different cooperative benefits. Furthermore, we provide robust evidence that species range size is the key concept to distinguish two cooperative benefits and provide empirical evidence for future studies in different taxa.