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When it comes to a healthy biodiversity, more species are not necessarily better. Yet this idea has not always been the case. True, many introduced plants and animals can serve very useful purposes, not only in providing food and other biological resources for people, but also at times providing useful ecological services. It would be hard to imagine the Marshall Islands without imported coconuts, breadfruit, "iaraj," bananas and chickens.
Nevertheless, not only in the Marshall Islands, but worldwide, it is now becoming clear that the importation of any new species is a risky proposition. And once one of these species, often referred to as an invasive species or an aggressive exotic, becomes established, there is often no practical way to get rid of it. The damage it does is thus permanent and often whole ecosystems are forever changed. Guam, for example, lost most of its endemic and native birds and the culprit most often cited is the brown tree snake (Boiga irregularis - this same species of snake has been reported on Kwajelein and Wake). In French Polynesia, when the attractive decorative plant Miconia calvensens escaped from a botanical garden, it became the "purple plague" and is now considered to be the worst of all invasive plants throughout Pacific! Fortunately, while there are old reports of this species decades ago on Jaluit, it evidently died out and is no longer to be found in the Marshalls.
Aggressive exotics are notorious for causing the extinction of endemic species, since they often take over environment and positions the natives held in the ecosystems. Sometimes, the destructive nature of some species has not been realized until nearly 50 years after their introduction - long, long after they have become well entrenched in an area and far too late to do much about it.
Tangan-tangan has caused ecological disaster on Guam. It is only found to a limited extent in the Marshalls.
The spiraling whitefly is damaging important native plants and food crops alike.
So far, at least, the Marshall Islands have not suffered from invasive species to the totally disastrous extent of other places. No endemic species has yet been driven into extinction by the onslaught of exotics. Nevertheless, the land environments of the Marshall Islands are particularly vulnerable to the bad effects of introduced species since they contain so few native species. Furthermore, non-native species can bring with them diseases and parasites that can further harm native plants and animals. The recent infestations of the spiraling whitefly and mealybugs are cases in point.
Biological control can at times help to keep exotic species in check, but this is a very complicated process, and doesn't always work. And it usually means the introduction of more new species, and there are risks with any introduction, even those brought in for pest control. Pesticides and herbicides are another means often used to control exotics, but these again have the potential of backfiring and have been known to destroy the very native species that they were intended to protect.