Invaders Today, Natives Tomorrow?

Models of colonizing species and episodes from the annals of population biology tell us that colonists, including exotic species or potential “biological invaders” (“Biological Invaders,” 17 Sept., p. [1834][1]), are most vulnerable to local extinctions early in an invasion. Once a colonizing species gains considerable momentum in staking its evolutionary claim on a habitat or ecosystem, it becomes all but invincible. Therefore, it seems to me that it makes little sense to attempt to control well-established biological invaders (foreign colonists) with equally exotic control agents. Only in the earliest stages of a biological invader's population growth cycle would eradication be possible, but unfortunately this is the most cryptic phase of the colonizing strategy, making detection of a potential problem extremely difficult in many cases. I advocate the notion that the entire planet is, and has been, one mammoth mixed-bag of countless colonizing episodes, both in geological and in contemporary time. We are focusing a lot of attention on the invasions of species within very small scales of time, but Earth's intermingling of organisms from different continents and seas has been occurring for millions of years. Doesn't it therefore follow that in cases today where biological invaders have strong footholds, that they are best left alone? Isn't it possible that at some point these populations will be naturally controlled by new interrelationships with local species and climate? In other words, at some point biological invaders have the potential of becoming new or quasi-native species. # {#article-title-2} Investigations of biological invaders may be more complicated than it would first appear. For many potentially noxious pests, we do not have adequate information about their native distribution. For example, concern was raised in the 1980s when Bursaphelenchus xylophilus , a parasitic nematode that severely damages native pines in Japan, was found to be responsible for the rapid death of mature pine trees in the midwestern United States ([1][2]). Concern lessened, however, when it was determined that it was primarily exotic, non-native pines that were dying and that the nematode was probably a North American native species. Similarly, the soybean cyst nematode, Heterodera glycines , was first observed in North America in North Carolina in 1954. Records suggested that the nematode was introduced with shipments of tulips from Japan ([2][3]). In spite of quarantines, the nematode spread to every soybean-producing state and, in 1997, it was estimated to have reduced U.S. soybean production by 218 million bushels ([3][4]). Its rapid spread has led some researchers to suggest that the nematode may have been endemic to North America, existing on related weed hosts, and that its distribution expanded with increased soybean production. Another theory has implicated importation of soil from Japan in the late 1800s to obtain Bradyrhizobium japonicum for soybean root nodulation. Biotic surveys and inventories of native organisms are critical for the proper identification of biological invaders. 1. [↵][5]1. V. H. Dropkin 2. et al. , Plant Dis. 65, 1022 (1982). [OpenUrl][6] 2. [↵][7]1. N. N. Winstead 2. et al. , Plant Dis. Rep. 39, 9 (1955). [OpenUrl][8] 3. [↵][9]North Central Region-137 subcommittee on soybean disease losses, report on loss estimates for the U.S. 1996–1998 available at . [1]: /lookup/doi/10.1126/science.285.5435.1834 [2]: #ref-1 [3]: #ref-2 [4]: #ref-3 [5]: #xref-ref-1-1 "View reference 1 in text" [6]: {openurl}?query=rft.jtitle%253DPlant%2BDis.%26rft.volume%253D65%26rft.spage%253D1022%26rft.atitle%253DPLANT%2BDIS%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [7]: #xref-ref-2-1 "View reference 2 in text" [8]: {openurl}?query=rft.jtitle%253DPlant%2BDis.%2BRep.%26rft.volume%253D39%26rft.spage%253D9%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [9]: #xref-ref-3-1 "View reference 3 in text"