Here and there and everywhere: The invasion experience differs among islands for the bamboo orchid

Background/Question/Methods

Arundina graminifolia, the bamboo orchid, is native to Asia-Pacific, but has been introduced as an outdoor ornamental plant in many parts of the tropics. In the Hawaiian Islands, naturalized populations were reported around 1940 where it was widely cultivated; in Puerto Rico, the same was true in 1982.  Because of the differences in introduction time and apparent varying densities, we seek to determine the cause of differences of Arundina graminifolia in both of these localities and shed light on its invasion process.  We studied the populations in terms of their reproductive biology to understand the differences in density. We also used species distribution modeling to study the two populations in terms of their environmental conditions. To accomplish these goals we collected data on flower morphology, reproductive success and presence localities in its invasive range (Hawaii and Puerto Rico) and its native range. For the species distribution modeling we used the maximum entropy modeling algorithm software MaxEnt where we ran different models that varied in their sample locality data (e.g. using native points, Hawaiian or Puerto Rican localities only).  This process was done to separate the relative effect of the localities in each of the potential distributions.

Results/Conclusions

Fruit production in Hawaii was much greater than in Puerto Rico. There were also differences in flower morphology, where the Puerto Rican orchids tended to have bigger flowers than those of the Hawaiian populations. The greater abundance of Arundina in Hawai'i relative to Puerto Rico is likely a consequence of both higher reproductive success and a longer residence time. We obtained 149 total localities of the bamboo orchid for Hawaii, Puerto Rico and its native range. When we predicted the distribution of Arundina to Hawaii and Puerto Rico separately we found that the variables with the greatest contribution varied across the two localities. Also, abiotic conditions varied considerably between Puerto Rico and the Hawaiian islands. Because of this situation we were unable to predict accurately the potential distribution of one locality using the distribution of another. We also found that the variability of the two invasive localities was within the native range variability, thus suggesting that niche expansion has not occurred. Arundina graminifolia has occupied a wide range of environmental conditions within its native range which enhances its capacity to invade other regions.