Density-dependent seed predation in Attalea geraensis Barb. Rodr. (Arecaceae) caused by bruchid beetles in the Brazilian Cerrado

Abstract Palms are an important component of Neotropical communities as they are often diverse and abundant. In some areas, palms occur in high density and act as limiting factor in tree recruitment by limiting tree seedling and sapling abundance. In this study, I evaluated the intensity of seed mortality caused by insects in Attalea geraensis, in a large area of preserved Cerrado (Serra do Cabral, MG, Brazil) during wet season when both A. geraensis fruits and bruchid beetles were abundant. I collected a total of 63 infructescences which had from 3 fruits and 7 seeds to 82 fruits and 251 seeds. Endocarps had from 1 to 6 seeds. Seed mortality per infructescence due to beetles (Pachymerus cardo) was intense, and increases positively and disproportionally according to seed number per infructescence. Besides that, average proportions of seeds preyed upon by insects were consistently high (> 0.83), irrespective of seed number per endocarp. Positive density-dependent seed mortality caused by specialized natural enemies has been assumed to promote species rarity, an important feature of species coexistence in Neotropical forests. Then, the intense seed mortality documented in this study suggests that seed predators may contribute to the richness and diversity of plant species in the Cerrado, the richest and most endangered savanna in the world.

摘要：棕榈科植物是新热带区群落的重要组成部分，因其通常兼具丰富的物种多样性与较高的种群丰度。在部分区域中，棕榈科植物种群密度极高，通过抑制树木幼苗与幼树的种群数量，成为树木更新的限制因子。本研究于巴西米纳斯吉拉斯州卡布拉尔山（Serra do Cabral, MG, Brazil）的大面积原生塞拉多（Cerrado）稀树草原生境中，在盖氏椰子（Attalea geraensis）果实与豆象甲虫均大量出现的湿季，评估了该物种种子被昆虫取食导致的死亡强度。研究共收集63个果序，单个果序的果实数量介于3至82枚、种子数量介于7至251粒不等；其内果皮含1至6粒种子。由卡多厚缘豆象（Pachymerus cardo）引发的单果序种子死亡率极高，且死亡率随单果序内种子数量呈正相关且非线性增长。此外，无论内果皮所含种子数量如何，昆虫取食导致的种子平均受害比例始终高于0.83。由专性天敌引发的正密度依赖型种子死亡，曾被认为可促进物种稀有性——这是新热带森林物种共存的重要特征之一。本研究记录的高强度种子死亡现象表明，种子捕食者或许有助于提升塞拉多稀树草原的植物物种丰富度与多样性，而塞拉多是全球物种最丰富且受威胁最严重的稀树草原生态系统。