Jos Stratford said:
On the other hand, if we talk more widely, i.e. by ecosystem, then certainly there are species some wish to remove that are 'native' to the overall ecosystem, i.e. our friend the Eagle Owl.
Of course they are native to the wider ecosystem, but, you still haven't given me absolute proof that the (already attenuated) harriers would not be at risk. All I'm saying (and said in my last posts) is that given that there is no pressing need for these owls to be here, since they almost certainly didn't arrive on their own volition, the sheer complexity of the relationships involved, and perhaps the irrepresentativeness of the overall ecosystem, means that I tend towards caution.
Jos Stratford said:
Basically, there is a complete gradient from 'natural' to 'unnatural', so it will be subjective to use this as a criteria.
I fully agree that the issue of 'naturalness' is one big grey area. It reminds me of an issue in geography we studied a while back-i.e. America is an MEDC, and Malawi is an LEDC, but what comes inbetween? Blue tit vs. Eagle Owl? The trouble is, if we see the complexity of deciding what is an invasive species, and then decided to ignore the issue, trouble ensues.
In the abscence of any definites, I always think that championing the species that have been there for a 'while' (how long is a piece of string I wonder), i.e. a highly conservative viewpoint, offers the best bet against the chance of entrance of highly destructive invasive species. The question of the species that get here by their own volition is a tricky one, especially due to the effects of anthropogenic climate change etc.
Even if we discount any notion of naturalness, what do we replace it with? The rather alien concept of biodiversity? Aesthetics? Some criteria have to be used to avoid an absolute laissez-faire viewpoint.