Comment on: The last uninvaded frontier?
One thing I feel compelled to note is that it can't be the rule that introduced exotics decrease biodiversity. Or else each exotic plant introduced to the Hawaiian Islands over the past 28 million years would have reduced biodiversity. You can't have much biodiversity if every introduction results in the loss of one established species. Errr...you can't have any biodiversity because the second exotic plant species would simply have replaced the first...and the third species would have replaced the second...
It could certainly be prudent to play it safe by arguing against the introduction of any species anywhere...but I think the priority should really be determining why some introduced species increase, rather than decrease, biodiversity.
The first plant to establish in Hawaii was like the first person on the bus. They had their pick of seats. It would be surprising for the second person to board the bus and force the first person out of their seat. "Hey, that's my seat!" It's not the greatest analogy because we have to imagine people being better suited to certain seats on a bus.
How many seats (microhabitats) are there in Hawaii? We can imagine an epiphyte boarding the bus and seeing that all the seats were taken..."it's ok, I prefer sitting on the roof". Epiphytes have no problem sitting in really uncomfortable seats. That's why they really increase the biodiversity to space ratio.
When I spent three years in the jungles of Panama...I really can't say that I saw a lot of people sitting on top of the buses. Epiphytes were the exception rather than the rule. Then again, I spent most of my time on the "drier" Pacific side.
Oncidium cebolleta grows in the dry forests of the Americas and Dendrobium canaliculatum grows in the dry forests of Australia. I would be extremely surprised if their cross introductions resulted in the loss of biodiversity. There are plenty of empty uncomfortable seats. Or maybe they would say to each other like two old time western gunslingers..."this here town ain't big enough for the two of us".
Epiphytic orchids, unlike other epiphytes such as bromeliads, rarely ever have high density populations. Generally they are few and far between. For me this seems to indicate that the rule for introduced orchids will not be a reduction in biodiversity.
Not sure if I'm remembering/interpreting a paper correctly...but a study of established reed stem Epidendrums in Hawaii seemed to indicate that they've already started to noticeably differentiate in the past 50 or so years since they've naturalized. It's pretty amazing how quickly they've adapted to the selective pressures of a new environment. I wonder how long it would take for them to become a new subspecies...and eventually a new species.