Population dynamics of epiphytes related to canopy structure and dynamics.

Epiphyte populations are distributed in a three-dimensional space, which is defined by their supporting trees and presents substantial gradients of microclimate, resources, and substrate. As most epiphytes die when falling to the ground with a breaking branch, their population dynamics is strongly dependent on the dynamics of the trees and branches they grow on. Both, the different micro-habitats in the canopy, resulting in niche separation, and teh high rates of disturbance, preventing dominance of a few species, are considered to be important contributors for their high diversity in tropical rainforests. While some aspects of epiphyte population dynamics have been studied in several species and matrix models have been developed for a few, none of these includes the complex relationships between tree zonation and dynamics on epiphytes and on their distribution within the canopy. The project aims to develop population models for three orchid and five bromeliad species in a population in a Mexican humid montane forest studied since 1992, partly drawing on previously recorded data. It will include studies of growth, mortality, flower production, pollination, seed production, and germination as related to the plants` position within the trees. Population genetic analysis will help to identify to what exent the spatial distribution is related to genetic distance and thereby inform about the geneflow within the population . Matrix and individual-based population models will be important tools to compare between species, to identify bottlenecks in a species`life cycle and to unterstand the complexities of the dynamics in rainforest canopies.