DISSERTATION RESEARCH: The influence of landscape heterogeneity and mycorrhizal fungi on the distribution of an epiphytic orchid and its genetic variation

森林砍伐威胁着热带地区的生物多样性，不仅因为减少了森林的数量，而且还因为将剩下的森林分割成小而孤立的斑块，物种可能无法到达这些斑块，或者物种一旦到达那里就无法生存。附生植物是一种生长在其他植物上而不是在地面上的植物，是许多物种丰富的热带森林生物多样性的重要组成部分，其中许多附生植物是兰花。兰花的种子很小，风可以把它们吹到很远的地方，所以它们可以从一片森林传播到另一片森林。然而，这些微小的种子如果没有特殊真菌的帮助就无法生长，这种真菌被称为菌根真菌，它为兰花提供营养。如果一片森林中缺少真菌，兰花一旦到达那里就无法存活。这项研究将测试究竟是种子的传播还是真菌的缺乏使兰花无法在热带森林中生长。研究工作将集中在一种在哥斯达黎加被大量使用的中高海拔森林中发现的兰花，并结合美国的分子遗传学和哥斯达黎加的实地实验。由于热带附生植物是全球最受威胁的物种之一，因此本研究对自然资源保护具有实用价值。这项工作应该提供有价值的见解，了解将热带森林划分成小块的特殊方式可以影响生长在热带树木上的许多兰花，无论是通过导致种子不足还是通过破坏兰花所依赖的特殊生态关系。研究结果应该有助于指导保护和恢复热带森林物种多样性的工作。此外，该项目将培养热带野外研究和分子生物学的研究生和本科生，加强国际科学合作。

Deforestation threatens biodiversity in the tropics, not only by reducing the amount of forest, but also by dividing the forest that remains into small, isolated patches that species may not be able to reach or where species may not be able to survive once they get there. Epiphytes, plants that live atop other plants instead of on the ground, are a major part of the biodiversity in many species-rich tropical forests, and many of these epiphytes are orchids. Orchids have tiny seeds that wind can move over long distances, so they might be able to travel from one patch of forest to another. However, the tiny seeds cannot grow without the aid of specialized fungi,known as mycorrhizal fungi,that provide the orchids with nutrients. If the fungi are missing from a forest patch, the orchids will not survive once they get there. This research will test whether it is the dispersal of the seeds or the absence of the fungi that keeps orchids from growing in patches cut from tropical forest. Work will focus on Epidendrum firmum, an orchid found in the heavily used, mid-elevation forests of Costa Rica, and use a combination of molecular genetics in the U.S. and field experiments in Costa Rica. Because tropical epiphytes are among the most globally threatened groups of species, this research has practical value for conservation of natural resources. The work should provide valuable insights into the special ways in which dividing tropical forests into smaller patches can affect the many orchids that grow on tropical trees, whether by causing seeds to fall short or by disrupting the special ecological relationships upon which the orchids depend. The results should help guide efforts to conserve and restore the diversity of species in tropical forests. Furthermore, the project will train graduate and undergraduate students in tropical field research and molecular biology, and strengthen international scientific collaboration.