Data from: Exceptional avian herbivores: multiple transitions toward herbivory in the bird order Anseriformes and its correlation with body mass

Herbivory is rare among birds and is usually thought to have evolved predominately among large, flightless birds due to energetic constraints or an association with increased body mass. Nearly all members of the bird order Anseriformes, which includes ducks, geese, and swans, are flighted and many are predominately herbivorous. However, it is unknown whether herbivory represents a derived state for the order and how many times a predominately herbivorous diet may have evolved. Compiling data from over 200 published diet studies to create a continuous character for herbivory, models of trait evolution support at least five independent transitions toward a predominately herbivorous diet in Anseriformes. Although a nonphylogenetic correlation test recovers a significant positive correlation between herbivory and body mass, this correlation is not significant when accounting for phylogeny. These results indicate a lack of support for the hypothesis that a larger body mass confers an advantage in the digestion of low-quality diets but does not exclude the possibility that shifts to a more abundant food source have driven shifts toward herbivory in other bird lineages. The exceptional number of transitions toward a more herbivorous diet in Anseriformes and lack of correlation with body mass prompts a reinterpretation of the relatively infrequent origination of herbivory among flighted birds.

植食性（Herbivory）在鸟类类群中极为罕见，学界普遍认为其演化主要集中于大型无飞行能力鸟类类群，相关依据为能量限制约束，或是植食性与体型增大存在正向关联。雁形目（Anseriformes）涵盖鸭、鹅与天鹅，该目几乎所有类群均具备飞行能力，且其中多数类群以植食性为主。然而目前仍无法明确植食性是否为雁形目的衍生特征，也不清楚以植食性为主的食性究竟独立演化过多少次。本研究整合了200余项已发表的食性研究数据，为植食性构建了连续性性状；通过性状进化（trait evolution）模型分析，结果支持雁形目内至少发生过五次独立的、以植食性为主的食性演化转变。尽管非系统发育相关性检验（nonphylogenetic correlation test）显示植食性与体质量之间存在显著正相关，但在纳入系统发育（phylogeny）因素进行校正后，该相关性便不再具有统计学显著性。上述结果表明，“更大体型能够提升低质量食物的消化优势”这一假说缺乏实证支撑，但本研究并未排除“转向更为充足的食物来源推动了其他鸟类类群向植食性演化”这一可能性。雁形目内植食性食性的演化转变次数异常繁多，且该食性与体型并无显著相关性，这一发现促使学界重新审视具飞行能力鸟类中植食性起源相对稀少这一现象。