Seed predation by macaws favors fruits with less seeds and thicker endocarps in the palm Attalea phalerata

ABSTRACT When foraging on a specific range of fruits or seeds, animals can represent a natural selection force, affecting plant population realized fecundity. Most studies have focused on characteristics of dispersed seeds, but the higher predation of seeds of specific size or shape is also an important force that influences the populations’ realized fecundity and can help to understand patterns of plants genetic variability. In the Brazilian Pantanal, we investigated the predation of Acuri (Attalea phalerata) palm fruits by macaws, whose seeds go intact through tapirs digestive tract and then are deposited on latrines, where they are often consumed by seed predators. We found 251 fruits, containing between 1 and 5 seeds per fruit; 170 were intact and 81 had been partially damaged by macaws, mostly those containing 3 or 4 seeds per fruit and with thin endocarps. We argue that the higher consumption of fruits with these traits reflects a trade-off in the energy spent by macaws to open the fruits and the energy provided by them. Higher predation on 3-4 seeded fruits favors the selection of 1-2 seeded fruits, revealing a selection force opposed to the one exerted by bruchids and small rodents, which favors multi-seeded palm fruits.

摘要：当动物在特定类群的果实或种子上觅食时，会构成一种自然选择压力，进而影响植物种群的实际繁殖力。现有多数研究均聚焦于扩散种子的特征，但特定大小或形状种子的更高捕食率，同样是影响种群实际繁殖力的重要因素，有助于阐明植物遗传变异的分布格局。在巴西潘塔纳尔湿地中，我们针对金刚鹦鹉对阿库里椰子（Attalea phalerata）果实的捕食行为展开了调查。该棕榈的种子可完整通过貘的消化道，随后被排泄至粪便堆中，而这些种子常会被其他种子捕食者取食。本次调查共收集到251份果实，单果内含1至5枚种子；其中170份完好无损，81份已被金刚鹦鹉部分破坏，受破坏的果实多为单果含3至4枚种子且内果皮较薄的个体。我们认为，金刚鹦鹉对具备上述特征果实的更高取食率，反映了其破开果实所需消耗的能量与果实提供的能量之间存在权衡关系。对3至4枚种子果实的更高捕食率，会倾向于选择单果含1至2枚种子的个体，这揭示了一种与豆象及小型啮齿类所施加的选择压力相反的选择力——后者更偏好多种子的椰子果实。