Mixed evidence of a commensal relationship between a rare epiphytic orchid and cohabiting bryophytes

The co-occurrence of orchids and bryophytes at occupied sites on host trees has been documented on several occasions, particularly in the tropics, and it may represent an important symbiotic relationship that supports epiphytic orchid populations. Despite continuing interest from ecologists, the specific life history traits that are affected by associations of orchids with bryophytes, and how they are affected, remain unclear. Clarifying the nature of the association will improve our understanding of orchid ecology and have practical implications for applied conservation efforts, particularly for rare species in restricted habitats. In this study, we explored the relationship between the abundance of bryophyte cover on host trees and various life history traits related to size, survival and reproduction of a rare tropical epiphytic orchid, Lepanthes caritensis. The results demonstrated that bryophyte abundance on host trees had variable effects on individual aspects of an orchid's life history. Orchid recruitment was positively correlated with the abundance of bryophyte cover, but survival and flower production were negatively correlated with bryophyte abundance. Our findings revealed that an apparent commensal symbiotic relationship between L. caritensis and bryophytes exists at the recruitment stage, but this is lost during later life stages, when the abundance of bryophytes appears to negatively affect this species.