Crop size influences pre-dispersal seed predation in the Brazilian Cerrado

ABSTRACT Many pre-dispersal seed predators are specialized insects that rely on seeds for larval development. These insects may respond to the amount of seeds produced by a plant (i.e. crop size), increasing the proportion of seeds damaged with increases in seed numbers. Large seeds have more resources and spend more time in plants to complete their development and are probably more prone to be preyed on by those insects than small seeds. Here I tested how crop size and seed mass influence pre-dispersal seed predation in plants from the Cerrado savannas of Brazil. I related plant crop size to pre-dispersal seed predation for Xylopia aromatica and Erythroxylum pelleterianum. A literature review was performed to test if seed mass may explain among-species differences in pre-dispersal seed predation. Pre-dispersal losses increased proportionally to crop size in the two species investigated, but some species show positive or no density-dependent seed predation in literature, indicating that seed losses are not a simple function of crop sizes. Seed mass did not explain pre-dispersal seed loss differences among 14 species with data available. Pre-dispersal losses are often small and probably less important than seed dispersal and establishment limitation for plant recruitment in Cerrado savannas.

摘要 许多种子扩散前捕食者（pre-dispersal seed predator）为特化昆虫，其幼虫发育完全依赖植物种子。此类昆虫会响应植物的种子产量，即结实量（crop size），随种子数量增加，受损种子的比例随之升高。大种子蕴含更多资源，且在植株上完成发育的时长更长，相较小种子更易被此类昆虫捕食。本研究以巴西塞拉多稀树草原（Cerrado savannas）的植物为研究对象，探究结实量与种子质量如何影响种子扩散前捕食（pre-dispersal seed predation）。针对Xylopia aromatica与Erythroxylum pelleterianum两个物种，本研究将植株结实量与其种子扩散前捕食率进行关联分析；同时通过文献综述，检验种子质量能否解释不同物种间种子扩散前捕食率的差异。研究结果显示，两种受试物种的种子扩散前损失量均随结实量成比例升高，但现有文献显示部分物种存在正密度依赖型种子捕食或无密度依赖的种子捕食现象，这说明种子损失并非仅由结实量单一决定。在纳入现有数据的14个物种中，种子质量无法解释其种子扩散前损失量的差异。塞拉多稀树草原中，种子扩散前损失通常较低，其对植物种群补充的影响可能弱于种子扩散与定植限制。