There goes the neighborhood: Reproductive success of Bletia patula when Spathoglottis plicata moves in

Background/Question/Methods One of the challenges of invasive species biology is knowing whether or not a naturalized species is invasive before dramatic ecosystem changes occur. In Puerto Rico, the exotic orchid, Spathoglottis plicata, has naturalized and spread rapidly over the last two decades. It is abundant and occupies the same habitat as the native orchid, Bletia patula. The two are hosts to the same native florivorous weevil, Stethobaris polita, a specialist on orchid flowers. We ask whether high population densities of Spathoglottis plicata affect the reproductive success of Bletia patula by elevating the abundance of the weevil. We measured local densities of the orchids where the two species grow together and also where B. patula grows in absence of S. plicata. We measured female reproductive success of Bletia at all sites. We also monitored the abundance of weevils and the extent of floral damage they cause on Bletia patula. In addition, we experimentally tested in vitro whether weevils preferred one species to the other. Finally, we modeled the distribution of both orchid species to predict the extent to which the two species may interact.

Results/Conclusions Preliminary data indicate the number of weevils per Bletia inflorescence tends to be higher where S. plicata is also present. These data also show a significantly higher flower and fruit production for B. patula where S. plicata is absent. The weevil choice experiments show that the beetles do not prefer flowers of one species to the other. The current distribution of the native Bletia patula is almost completely limited to the northern karst region of Puerto Rico whereas the naturalized S. plicata has established in nearly all moist to wet habitats of the island with a high frequency of populations in the same region as B. patula. The Spathoglottis is expected to occur wherever B. patula exists. Our data thus far suggest that Spathoglottis plicata is an invasive species. It negatively affects the reproductive success of the native orchid, Bletia patula, through an elevation in the frequency and abundance of the florivorous weevil.