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 Whose afraid of invasive species?


The why of the emergence and extinction of species is always rather hard to come by, since we want to understand the how first, anyway. From a mere biological view, rather than an anthropological one, conservation biology (as an extension of environmentalism), for instance, is as much anti-evolution as intelligent design. Both are doctrines, one declaring Nature to be sacred, the other that only humans have a sole. Both seek to comfort people who either worry about the loss of environment or a loss of belief in a God. If the goal of evolution were man, then both doctrines are indeed valid expressions of the notion that man occupies a special place within Nature.

Obviously a healthy environment is necessary, since our only source of food are fellow creatures living from clean air, soil and water. The goal here is not to shrug our shoulders regarding pollution and destruction of habitats. The goal is to get an understanding of our understanding of evolution. I want to start here with a discussion of the invasive or alien species problem. Invasive species are seen as problematic and as agents of extinction of native species (see Global Invasive Species Program and the Invasive Species Specialist Group). Yet we should look at invasive species not simply as a problem of invasion, but one of change (mostly facilitates by our technology and migration patterns).

The outcomes of 'invasion' is a form of evolution (think of finches invading the Galapagos islands). While it affects native species, species richness is often not diminished, particularly for plants, but can be enhanced. Invariably, species composition will change. How this change threatens a 'healthy' ecosystem, may be a matter of discussion. But mostly it is viewed as having negative outcomes related to human commercial interests, like the introduction of predators, pathogens and weeds. A recent article in the Proceeding of the National Academy of Sciences, USA, by Dov Sax and Steven Gaines (www.pnas.org/cgi/doi/10.1073/pnas.0802290105) focusing on island biodiversity find among other things the following:

"Overall, patterns of extinction and naturalization have led to large change in net species richness on islands around the world. Bird richness on most oceanic islands has remained largely unchanged, because the number of extinctions has been largely matched by the number of exotic birds that have become naturalized. This relative consistency in net bird richness may be important in understanding and predicting future extinctions, but is not a 'good' thing from a conservation perspective, because it means that many unique endemic species have been lost and replaced by more cosmopolitan species from mainlands. In contrast to birds, mammal richness has increased dramatically, particularly on oceanic islands, which have few native mammal species. Freshwater fish richness has also increased, because few native fishes have gone extinct (at least so far), whereas many exotic species have become naturalized. Invertebrate richness may also have increased, because many invertebrates have become naturalized on islands, e.g., >2,500 species on Hawaii alone, but records of extinction are less certain, so it is difficult to know how net richness has changed without additional investigation. Finally, vascular plants (land plants) have seen dramatic increase in richness across both continental and oceanic islands, because many exotics have become naturalized, whereas few native species have gone extinct."

These findings have been published as part of a series of Biodiversity and Extinction by the National Academy of Sciences (see the Sackler Colloquium on biodiversity and extinction). Although there are quite a few well documented stories of great changes brought to some regions upon import (intentional and unintentional) of mostly animals and pathogens, very rarely plants, a majority of reported invasive species events have no factual documentation of damage. It is easy to identify invasive species and elaborate some future damage due to 'extinction debt' (see Avise, Hubbell and Ayala, www.pnas.org/cgi/doi/10.1073/pnas.0802504105), but most is speculation (... "E. O. Wilson estimated that the Earth is currently losing about 0.25% of its remaining species per year. Such estimates are educated guesses because the represent extrapolations to taxa that undoubtedly are disappearing even before they can be identified.") and denial (... " Sax and Gaines examine historical records from islands around the world to ask whether native plant species likewise often have gone extinct when exotic plants were introduced and became naturalized. The answer seems to be a clear no, at least yet." ibid.).

Predicting the future is a tough job. I opt for a little more faith in Nature. Even E. O. Wilson (the founder of sociobiology and what is now known as evolutionary psychology) says that life is resilient. Much of doomsday thinking is a reflection of human hubris that we take ourselves to seriously and important and omnipotent, as if man, like God, has the ability to destroy life as we know it. A little humility should be in order.

 Copyright © 2000-2009 Lukas K. Buehler