Here are more comments from my interview with Kim Hill:
‘…we do not have to accept a future that sees our ecosystems as homogeneous with everything else, comprised of international tramp species and the few natives that can persist with them’
‘…there’s a tonne of [introduced] plants out there that if we let go they’ll change landscapes and there’ll be nothing. I mean we’re talking monospecies…’
People are terrified that we are going to end up with a small number of cosmopolitan species (low diversity); that we’re just going to end up with rats, zebra mussels, brown tree snakes; that we’re going to lose our local and regional distinctiveness; and that introductions are ultimately going to be responsible for this diminution.
Well, maybe. But in New Zealand what we can say is that we have introduced tens of thousands of species, something over 26,000 plants, nearly 30 mammals, over 30 birds, tens of freshwater fish, hundreds of invertebrates, and so on.
Yet these additions have not led to corresponding extinctions and most of the extinctions that have occurred to date have been due to overharvesting and habitat loss. That’s not to say that competition and predation are not factors in the extinction of species too, but simply to stress the point that they are usually factors in association with a range of others.
The case for diversity
And our ecological understandings of what happens when you introduce species have changed too. We used to think that highly diverse ecosystems were able to repel invaders. But it turns out it’s not true. Highly diverse native ecosystems tend to also have high numbers of introduced species. So diversity itself seems to be no protection from change.
This is not to say that that diversity is necessarily a good thing, of course. Many native ecosystems, for example, have comparatively low levels of diversity – native beech forests and raupō wetlands being a couple of cases in point. The very idea that diversity is good is, of course, another value judgment. What we can say however is that species richness has increased on a local, regional, and national level due to introductions in New Zealand and elsewhere around the world.
Global species richness has declined, sure enough, but as British ecologist Chris Thomas recently noted, we don’t yet know if that may come to be counterbalanced to some extent by the evolution of new genes, varieties, and species. And studies in recent times of rapid evolution in human-influenced environments seem to show that speciation, whether through divergence, hybridisation or other mechanisms, may be happening much faster than we once thought.
Featured image © Creative Commons.