Seed banks, seed mortality, and the role of fungal communities in neotropical forests

Depending on their abundance, distribution and host specificity, fungi, and especially fungal pathogens, have the potential to shape the distribution and abundance of susceptible hosts. My dissertation research examined the ecology and interactions of fungi and seeds in tropical seed banks, and the abiotic factors that influence host-fungal interactions. Working at Barro Colorado Nature Monument (BCNM) Panama, the La Selva Biological Station, Costa Rica, and the Yasuni National Park, Ecuador, I determined that fungi cause significant mortality at the seed and pre-emergence stage in the archetypal tropical pioneer genus Cecropia. I integrated empirical measurements of seed mortality in the field with molecular tools to link specific fungal taxa with seed fate. Cecropia species appear to be equally susceptible to fungal infection during the seed and emerging seedling stage. Further, most Cecropia seeds are susceptible to colonization by fungi, pathogenic or not; > 80% of seeds collected from soil yield a fungal isolate when cultured. These results provided a first genetic characterization of fungal taxa influencing seed and seedling mortality in tropical forests, and showed how the composition of the fungal community varies with respect to host and habitat. I demonstrated that spatial differences in fungal community composition can influence seed survival. Finally, I showed how temporal variation in seed survival and fungal community composition are likely driven by abiotic factors in the environment.;Index words. Ascomycota; Cecropia; fungi; tropical forest ecology; seed bank; pioneer species; pathogens; ITS; Barro Colorado Island, Panama; La Selva, Costa Rica; Yasuni, Ecuador; recruitment limitation.