Do epiphytes affect the fitness of their phorophytes? The case of Tillandsia recurvata on Bursera copallifera

The studies about the negative effect of epiphytes on their phorophytes show contradictory results and are based on limited variables (e.g., shoot survival). On branches of Bursera copallifera, we experimented with the transplantation/removal of Tillandsia recurvata and artificial tussocks, measuring shoot survival, growth, generation of new shoots, and production of inflorescences and fruits. Most single traits did not differ between treatments. The generation of new shoots was lower in the treatments where T. recurvata was present and increased in the branches where it was removed. The lowest shoot survival was in the treatments where T. recurvata was present or was removed. Removing T. recurvata increased plant relative fitness, and it was 43% lower in branches with T. recurvata. Tillandsia recurvata is a structural parasite of B. copallifera. A negative effect of epiphytes on their phorophytes appears counterintuitive since it would not be evolutionarily stable for an epiphyte to shorten the lifespan of its support. Tillandsia recurvata populations are concentrated on B. copallifera branches between 2-4 cm in diameter, while smaller branches are mostly empty, so it is possible that the negative effect of T. recurvata occurs in the smallest branches, explaining why T. recurvata populations are biased to larger branches.