Immigration and invasion - biological xenophobia?

One of the hottest political topics in Singapore today is the issue of immigration: your 'foreign talent' may be my 'job-stealer', as the debate continues on just how much immigration is desirable for a small country like ours.

In the field of biological conservation, a similar conflict has popped up, as reported recently in the Boston Globe. Conservationists have traditionally spoken of 'introduced' vs. 'native' species, with the least desirable introduced species being termed 'invasive'. But a number of vocal critics have spoken up to say that this is simply nativism - an unthinking bias in favour of the supposedly native. They contend that the division between native and non-native is arbitrary and unscientific, in part because many familiar species were originally imports from elsewhere, and also because the environment is constantly changing, and species are continually migrating, and to try to freeze a community in time is akin to gardening nature. The author Michael Pollan went as far as to say that species-nativism was "xenophobic".

Classical examples of species invasions include the rabbit and cane toad in Australia, and the European starling in the USA (for which Shakespeare, bizarrely enough, is to blame). In Singapore, Clidemia hirta or Koster's Curse (a native of the Americas) has a tenacious foothold on forest fringes and clearings, preventing the re-establishment of native vegetation.

However, much of our modern landscape is precisely the product of introduced species. The grand arching wayside tree canopies that provide shade and shelter are often rain trees, Samanea saman, which are native to Brazil. These are perhaps the 'foreign talent' side of the argument.

We justifiably take pride in our native species, and among the popular Science Centre guidebook series is a volume on cultivating native plant species. But for an island as small as Singapore, does it make sense to speak of 'native' species? What hope is there of eradicating non-native species, anyway?

Ultimately, it may simply be a matter of rhetoric. The disagreement is not over the substance of the matter but the language that we use to talk about it. As the Globe article says:

Just as most ecologists accept that only a fraction of non-native species are harmful, the anti-nativists, when pressed, will admit that unequivocally destructive species like the Asian longhorned beetle should be reined in. Their disagreement lies more in how we should talk about the issue, how we justify our interventions and how we label the species we want to eradicate.

That is to say: when we call a species an 'invasive species', it's not enough simply to say that it's non-native and hence must be eradicated for that reason alone. We must be clearer about what 'invasiveness' means, and be able to justify our assertions about their harmfulness and undesirability.