Gilardi James D, Toft Catherine A
Department of Evolution and Ecology, University of California Davis, Davis, California, United States of America.
PLoS One. 2012;7(6):e38293. doi: 10.1371/journal.pone.0038293. Epub 2012 Jun 5.
Generalist herbivores are challenged not only by the low nitrogen and high indigestibility of their plant foods, but also by physical and chemical defenses of plants. This study investigated the foods of wild parrots in the Peruvian Amazon and asked whether these foods contain dietary components that are limiting for generalist herbivores (protein, lipids, minerals) and in what quantity; whether parrots chose foods based on nutrient content; and whether parrots avoid plants that are chemically defended.
METHODOLOGY/PRINCIPAL FINDINGS: We made 224 field observations of free-ranging parrots of 17 species in 8 genera foraging on 102 species of trees in an undisturbed tropical rainforest, in two dry seasons (July-August 1992-1993) and one wet season (January-February1994). We performed laboratory analyses of parts of plants eaten and not eaten by parrots and brine shrimp assays of toxicity as a proxy for vertebrates. Parrots ate seeds, fruits, flowers, leaves, bark, and insect larvae, but up to 70% of their diet comprised seeds of many species of tropical trees, in various stages of ripeness. Plant parts eaten by parrots were rich in protein, lipid, and essential minerals, as well as potentially toxic chemicals. Seeds were higher than other plant materials in protein and lipid and lower in fiber. Large macaws of three species ate foods higher in protein and lipids and lower in fiber compared to plant parts available but not eaten. Macaws ate foods that were lower in phenolic compounds than foods they avoided. Nevertheless, foods eaten by macaws contained measurable levels of toxicity. Macaws did not appear to make dietary selections based on mineral content.
CONCLUSIONS/SIGNIFICANCE: Parrots represent a remarkable example of a generalist herbivore that consumes seeds destructively despite plant chemical defenses. With the ability to eat toxic foods, rainforest-dwelling parrots exploited a diversity of nutritious foods, even in the dry season when food was scarce for other frugivores and granivores.
食草性泛化动物不仅面临着植物性食物中氮含量低且难以消化的问题，还受到植物的物理和化学防御机制的挑战。本研究调查了秘鲁亚马逊地区野生鹦鹉的食物，探讨这些食物是否含有对食草性泛化动物而言具有限制作用的膳食成分（蛋白质、脂质、矿物质）以及含量如何；鹦鹉是否根据营养成分选择食物；以及鹦鹉是否会避开具有化学防御机制的植物。
方法/主要发现：在两个旱季（1992 - 1993年7 - 8月）和一个雨季（1994年1 - 2月），我们对8个属的17种自由放养的鹦鹉在一片未受干扰的热带雨林中觅食102种树木的情况进行了224次实地观察。我们对鹦鹉食用和未食用的植物部分进行了实验室分析，并通过卤虫毒性试验作为脊椎动物毒性的替代指标。鹦鹉食用种子、果实、花朵、树叶、树皮和昆虫幼虫，但它们高达70%的食物是多种处于不同成熟阶段的热带树木的种子。鹦鹉食用的植物部分富含蛋白质、脂质和必需矿物质，以及潜在的有毒化学物质。种子的蛋白质和脂质含量高于其他植物材料，纤维含量较低。与未食用的可用植物部分相比，三种大型金刚鹦鹉食用的食物蛋白质和脂质含量较高，纤维含量较低。金刚鹦鹉食用的食物中酚类化合物含量低于它们避开的食物。然而，金刚鹦鹉食用的食物含有可测量水平的毒性。金刚鹦鹉似乎并非根据矿物质含量进行饮食选择。
结论/意义：鹦鹉是食草性泛化动物的一个显著例子，尽管植物有化学防御机制，它们仍会破坏性地食用种子。凭借食用有毒食物的能力，生活在雨林中的鹦鹉能够利用多种营养丰富的食物，即使在旱季其他食果动物和食谷动物食物匮乏的时候。
