Vertebrate florivory of vascular epiphytes: the case of a bromeliad

Abstract The avoidance of vertebrate herbivory is thought to be one of the possible drivers for the evolution of epiphytism. Scarce literature suggests that epiphyte herbivory is mainly related to insect attack on reproductive structures. In a pine-oak forest we observed almost all inflorescences of an epiphytic bromeliad (Tillandsia carlos-hankii) with signs of florivory; the degree of damage suggested that vertebrate herbivores could be involved. To assess the intensity of vertebrate florivory damage we recorded the percentage of damaged individuals in a 500 m2 plots during two flowering seasons. To identify possible vertebrate herbivores, we installed 20 mixed capture stations, 10 photo-traps focused on bromeliads and analyzed stomach contents of captured vertebrates. Florivory was observed on 62% of individuals during the first flowering season and 77% on the second; and average one individual lost 41% of reproductive structures. Vertebrates associated with florivory were a bird, Icterus bullockii (Aves, Passeriformes, Icteridae), a squirrel Sciurus aureogaster (Mammalia, Rodentia, Sciuridae), and mice, Peromyscus gratus, P. levipes and P. aztecus (Mammalia, Rodentia, Cricetidae). Our results suggest that vascular epiphytes are used as opportunistic resources for small vertebrates during seasons when preferred resources are scarce.

摘要 避免脊椎动物植食被认为是附生现象（epiphytism）演化的潜在驱动因素之一。目前相关研究较为匮乏的文献表明，附生植物（epiphyte）的花食性（florivory）主要与昆虫对其繁殖结构的取食相关。我们在一处松栎林中观察到，某附生凤梨科植物——铁兰（*Tillandsia carlos-hankii*）——的几乎所有花序均带有花食性取食痕迹；该损伤程度提示脊椎动物植食者可能参与了取食过程。为评估脊椎动物花食性损伤的强度，我们在两个开花季内，于500平方米的样地中记录了受损伤个体的占比。为识别潜在的脊椎动物植食者，我们布设了20组混合诱捕站，其中包含10台聚焦于凤梨科植物的相机陷阱（photo-trap），并对捕获的脊椎动物的胃容物进行了分析。首个开花季中，62%的个体出现花食性损伤，第二个开花季该比例升至77%；单株个体平均损失41%的繁殖结构。与花食性相关的脊椎动物包括：布氏拟鹂（*Icterus bullockii*，鸟纲Aves、雀形目Passeriformes、拟鹂科Icteridae）、金松鼠（*Sciurus aureogaster*，哺乳纲Mammalia、啮齿目Rodentia、松鼠科Sciuridae）以及鹿鼠属的*Peromyscus gratus*、*P. levipes*和*P. aztecus*（哺乳纲Mammalia、啮齿目Rodentia、仓鼠科Cricetidae）。本研究结果表明，当小型脊椎动物的偏好食物资源匮乏时，维管附生植物会被其当作机会性取食资源加以利用。