Influence of distance from conspecific and heterospecific co-flowering plants on pollination and fecundity in the nectarless orchid Dactylorhiza sambucina

Abstract

ABSTRACT Background The relative influence of both conspecific and heterospecific plant density on the fecundity of generalist rewardless plants is unclear. Aims To test whether distance from both conspecific and heterospecific plants influence pollen removal, deposition, and fruit set in the nectarless orchid, Dactylorhiza sambucina that co-flowers with the rewarding Ranunculus apenninus. Methods I experimentally translocated D. sambucina inflorescences and measured pollen removal and deposition rates. I measured plant height and distance to D. sambucina and R. apenninus plants in 30 D. sambucina patches of varying density. I quantified the proportion of pollen removed, pollinia deposited, and fruit set and tested whether these vary according to plant height and distance to both D. sambucina and R. apenninus. Results Translocated inflorescences outside the population had a higher proportion of pollen removal than control plants within the population, while pollinia deposition rates did not differ. Increased D. sambucina height increased pollen removal rates, while increasing distance from R. apenninus resulted in both increased pollen deposition and fruit set. Conclusion Pollination and fecundity of a nectarless orchid may increase with increasing distance from rewarding heterospecifics. This study improves our understanding of how the fecundity of rewardless plants is influenced by co-flowering plants.