Abstract
The ecology of hemiepiphytes is very poorly understood. More appalling is the lack of information on hemiepiphyte vital rates and demography. Such information is essential to understand the ecology, management and conservation of this group that is an important component of tropical forest. In this thesis, I aimed to fill
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some of these gaps in knowledge on hemiepiphyte ecology. I studied three sympatric secondary hemiepiphyte of the genus Heteropsis in the Colombian Amazon. The life cycle of secondary hemiepiphytes has two contrasting phases. The first occurs after germination and ends when the seedling climbs a host. As secondary hemiepiphytes lack the capacity to hold themselves upright they need to encounter suitable structures on which to climb. The observations on the host-searching behavior of the Heteropsis stems or shoots and the high similarity of the diameter distribution of hosts of Heteropsis seedlings that had just climbed a host, to that of all trees, palms, and lianas of ≥10 cm dbh in the plots were consistent for the three species. These results suggest that Heteropsis seedlings climb up a randomly encountered, nearby host, and that they adopt a random searching strategy instead of one directed by skototropism, as it was found on Monstera by Strong and Ray (1975). The second phase of the life cycle starts when a host has been found and the plant ascends. The vast majority of the seedlings climb up non-suitable hosts (81%). As a consequence, those individuals cannot complete their life cycle; because Heteropsis species must reach a threshold size before beginning to reproduce. Clonal propagation via shoot production allows Heteropsis to move from a non-suitable host to a suitable one. Once the seedling ascended a host the survival probability is very high (94-85%), all species grew very slowly in height (ca. 2 - 8 cm/year) with a substantial number of individuals (up to 62 %) not growing at all or shrinking over a two-year. The amount of light and the number of roots positively affects growth rates to some extent in Heteropsis macrophylla. The suitability of the host did not affect survival and growth of the three Heteropsis species in the short term. As very many recruited seedlings climb onto non-suitable hosts and as these plants may be able to reach suitable hosts through clonal reproduction, it is still possible that this lifecycle pathway through non-suitable hosts contributes substantially to the population growth rate (λ). According to elasticity and loop analyses, the small proportion of seedling that climb up on suitable host (19- 28%) and survive until they reach a reproduction state contribute more to λ than the large share of the seedlings that climb onto non-suitable hosts. The key to the maintenance of these populations is probably the long reproductive lifespan of these species.The source and sink dynamics results emphasize again thatλ’s highly depend on the restricted recruitment of seedlings on suitable hosts. I found that there is little scope for cultivation as an alternative to large-scale harvesting from natural populations. It is advised that harvesters prevent killing plants or pulling down the plants during root harvesting.
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