“Resolving the paradox of environmental quality and sociality: the ecological causes and consequences of cooperative breeding in two lineages of birds”

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Yu-Heng Lin (林宇恆), Shih-Fan Chan (詹仕凡), Dustin R. Rubenstein, Mark Liu (劉彥廷), and Sheng-Feng Shen (沈聖峰) (Aug 2019)

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Social animals occupy larger species range size

Hornbills (Tockus deckeni) and starlings (Lamprotornis superbus).
(Credit: Sheng-Feng Shen)

Abstract

Cooperatively breeding animals occur in virtually every ecosystem on earth. Comparative and biogeographic studies suggest that both benign and harsh, as well as stable and fluctuating, environments can favor the evolution of cooperative breeding behavior. The fact that cooperative societies occur in environments of such contrasting quality creates a paradox of environmental quality and sociality. The dual-benefits framework—which leads to the prediction that the ecological consequences of sociality (e.g. range size) vary depending on the benefits that individuals of each species receive by forming social groups—offers a potential resolution to this paradox. Here we use a case study of two avian lineages, starlings (Sturnidae) and hornbills (Bucerotidae), in which environmental unpredictability appears to have opposite effects on the evolution of cooperation to test the dual-benefits framework. Consistent with previous work, harsh and unpredictable environments promote cooperative breeding behavior in starlings, which in turn leads to larger geographic ranges. However, cooperatively breeding hornbills occur in benign and stable environments, but sociality does not influence range size. Our study suggests that the paradox of environmental quality and sociality arises largely because cooperative breeding is an umbrella term, encompassing social species that form groups for different reasons. We demonstrate that differentiating among the functional causes of social group formation is critical for developing a predictive framework for understanding the evolution of cooperative breeding behavior.

解決環境品質和社會性演化的悖論:促進兩類鳥類類群中合作生殖演化的生態原因與其後果

林宇恆,詹仕凡,Dustin R. Rubenstein,劉彥廷,沈聖峰

地球上幾乎每個生態系統均可見合作生殖的動物。比較研究和生物地理學研究顯示,良好與嚴苛、以及穩定和變動的環境皆有利於合作生殖行為的演化。合作生殖物種在這些品質相異的環境中存在的事實造成了環境品質和社會性演化的悖論。我們的雙重群體利益理論預測:社會性的生態後果(例如物種的地理分布範圍大小)取決於每個物種的個體透過組成社會群體所獲得的利益,因此這理論提供了對這一悖論的潛在解決方案。由於環境不可預測性對椋鳥科和犀鳥科這兩個鳥類類群合作生殖的演化,有相反的影響,我們就使用兩個鳥類類群,進行案例研究以測試雙重群體利益理論。與過去的研究結果一致的是,嚴酷和不可預測的環境促進了椋鳥的合作繁殖行為,因而使椋鳥有更大的物種地理分布範圍。然而,合作繁殖的犀鳥在良好和穩定的環境中出現,但其合作生殖與否則不影響物種的分布範圍大小。我們的研究表明,環境品質和社會性演化的悖論的形成主要是因為合作生殖是一個概括性術語,包含因不同生態原因而形成群體的社會性物種。我們的研究證明,區分社會群體形成的生態原因,對於進一步發展用於理解合作生殖行為演化的預測理論至為關鍵。