August 10, 2010

First stop: Tahiti

Assistant Professor of Biology, Queens College and The Graduate Center

Tahiti morning

Tahiti morning

PAPEETE, Tahiti | It is 7 am in Papeete, and the sunrise is beautiful, the smells are relaxing and for some reason I have a random Kinks song stuck in my head. Down here in the southern hemisphere, it is wintertime and the equatorial sun sets at 6 pm (all too early), with no angular lingering. After 14 hours on two planes and a six-hour time difference, my three students and I forced ourselves to stay up until 10 in order to get in synch with the local time zone. We sauntered through the grimy streets to the waterfront food carts and had ourselves some steak, frites, and tuna kabobs. Papeete is the largest city in French Polynesia—actually, it’s the only city in French Polynesia. We are really as far as you can get from all continental reach, which puts us roughly equidistant from Australia, the Americas and Antarctica.

We are here in the Society Islands to look for invasive species as part of an ongoing international project to examine the entire biological community at the DNA level, using a process known as DNA biocoding. This ecosystem-scale endeavor is manageable only on a relatively small, discrete and bounded system such as an island. The nearby island of Moorea is the project’s main site because it harbors a full range of complex tropical habitats—lowland forest, mid-elevation, mountain forest and marine coral. There are already two longstanding research stations here, providing us with an established infrastructure for our expedition. There really is no other place on the planet with all these characteristics. For more on the overall project, go to: http://mooreabiocode.org/

Though Moorea is the main event, it is here in Papeete, the central port of Polynesia, that has long served as the entry point for species coming in from all the world–carried here by the ballast water of cargo ships and various other conduits for hitchhiking species. I would not be surprised if most of the plants we see while walking around town came from other parts of the world in the last 50 years. But let us step back and note that the history of human expansion into Polynesia from Southeast Asia is one of humans and their invasive species sculpting newly colonized islands into “human ecosystems.” In fact, when looking for invasive species in Polynesia we have to partition and qualify what we mean by “natural” into “pre-human,” post-Polynesian, and … post-war.

Let us step back further and think about what’s actually meant by “natural” and unnatural manmade environments. They don’t form a dichotomy but a continuum. Modifying the natural environment so that it will yield more resources, be safer and more ascetically pleasing is as old as our species. Rather than being the “noble savage” in perfect harmony with our environment until some mythical fall from paradise, humans, in varying degrees, have always sculpted their surroundings to form human-centric ecosystems. One might appreciate the Mediterranean region’s citrus trees, olive groves, vineyards, wheat fields and nut trees as idealized natural beauty, but really none of these species are from this area. They are products of thousands of years of human interference with the natural environment and human-facilitated species invasions.

For volcanic Polynesian islands like Moorea and Tahiti, we can partition species “invasions” into a few vague categories. In the first scenario, after the volcanic island emerged from the ocean more than a million years ago, it got rained on by species from older islands—something predicted to continue until the island can accommodate no more species (a function of the island’s size). At this point the number of new species coming in is offset by a background species extinction, all of which is related to how geographically isolated the island is. This assumes, of course, that all species are equally suitable.

Another scenario is that a large burst of species settled on the island early on with later colonizations less likely because of interactions between competitive species. Although colonization and extinctions happen periodically, sometimes in bursts, a second way to introduce new species is by local in situ speciation—the formation of new species within an island. This seems to be quite common on islands, and it’s not very surprising given the isolation and the novel environments that can drive natural selection of traits that eventually result in reproductively isolated lineages and new forms (i.e. speciation).

After several waves of speciation and extinction, a third wave of species invasions occurred as humans expanded across the Pacific, bringing along their own “human ecosystem.” This bag of flora and fauna is a long list that includes pigs, fowl, crops, ceremonial plants, rats and parasites. This occurred only in the last couple of thousand years—maybe only hundreds—depending on where in Polynesia we are talking about, and in many ways falls within the normal spectrum of human environmental modification.

Finally, the forth major wave of invasions is what we are now experiencing and what we aim to characterize with modern genetic techniques. A huge genetic database has been accumulating as researchers from all over the world have come to Moorea to contribute to the DNA Biocode project. We can use this reference database as well as other global genetic databases to detect invasive species found here on the island. And that’s what we plan to do.

Tomorrow morning, we take the ferry to Moorea. I’ll talk to you from there.