| Characterized by the unique space they occupy in tropical forests, vascular epiphytes have increasingly been recognized as indicators for changes in environmental conditions, including climate, forest structure and biodiversity, and ecosystem health. Found in association with fungi, ants, birds, and other vertebrates, along with the host tree on which they are perched, epiphytes are a dominant component of mature tropical forest ecosystems. Epiphytes are less abundant in secondary forests, yet the factors limiting epiphyte distribution and abundance in secondary forests have been little studied. Seasonal tropical forests where epiphytes are found are under increasing pressure from anthropogenic disturbances and tropical storms. Given their highly symbiotic nature and importance in tropical forests, the studies presented in this dissertation were designed to increase our understanding of how populations of epiphytes get established in natural ecosystems.;I first describe the structure of epiphyte communities throughout mature, secondary, and wetland seasonal tropical forests of the Yucatan Peninsula. After conducting surveys in the field, I used logistic regression and principal components analysis to analyze the data and found epiphyte presence to be strongly related to the amount of light and amount of lichens covering the host bark. Host specificity in these forests was not observed. In Chapter 1, I describe how host tree and epiphyte species composition varied across the three forest types and discuss the suitability of these forest types for epiphyte establishment.;In October 2005, Hurricane Wilma passed over the study site, and I report the impact of this disturbance on the epiphyte populations. I used Shannon's diversity index and Soerensen's similarity index to compare epiphyte populations in the different forest types throughout El Eden Ecological Reserve as well as the change in these populations following Hurricane Wilma.;I used a combination of field and growth chamber germination experiments to explore the influences of temperature, humidity, vapour pressure deficit, and seed viability on epiphyte germination and establishment. Finally, I used stable isotopes to investigate the physiological ecology of epiphytes. In Chapter 4, I report on the flexibility of carbon assimilation for four con-generic epiphyte species and discuss the implications for epiphyte success in changing environments. |
