Population Dynamics of Epiphytes: the Influence of Host Branches

Epiphytes need to balance the chances and risks oflongterm survival and those of colonizing newbranches in their high-stress and high-risk canopyhabitats. Populations of three epiphytic orchids andfive bromeliads were declining except for the mostxeric species. High seedling mortality had onlylittle effects on population growth rates, which weremost sensitive to the survival of large stages. Branch characteristics related to light affected timeto germination, survival rates and the probability ofgrowing from the pre-reproductive to the reproductivestage. The breeding systems of the epiphytesinvestigated ranged from obligatory outcrossing tofacultatively self-pollinating. Species growing onsmall and less stable branches had a higher fruit setthrough self-pollination or other strategies, whichmay be of importance to compensate the highdisturbance on these substrates. However, high fruitset and substantial herbivory in reproductive organsof several species had only a limited effect onpopulation performance. Declining populationscombined with the increasing loss of natural habitatsmay lead to the extinction of species, especiallythose restricted to closed forests.