Floral Display, Reproductive Success, and Conservation of Terrestrial Orchids

Abstract

Almost a third of all species in the family Orchidaceae offer no reward to insect pollinators. In the absence of a reward, the number of flowers may be the most important component of insect attraction; however, the importance of the number of flowers in the inflorescence for fruit production has not yet been satisfactorily explored. We have examined reproductive success in the European orchid species Orchis morio in different years and at various locations. We have tested the following hypotheses: (i) For a species under given conditions, there exists an optimal number of flowers in the inflorescence, and plants with this optimal number of flowers are the most common ones in the population; (ii) Increase of the number of pollinators results in an increase in fruit set of the orchid. Neither of the hypotheses was supported by our data; however, our data suggest that fruit set may be positively correlated with the amount of rewarding co-flowering plants. Based on these findings, we propose that promotion of rewarding co-flowering plants, rather than augmentation of the presence of pollinators, seems to be a promising conservation strategy for nectarless orchid species.