Thanks for your comment, Jerry. I agree absolutely that the ecological change being brought about by human influence is quicker and more widespread - to a staggering degree - than that brought about by any other factor over recent millennia. We are in a period of mass extinction - or we're certainly heading that way. I grieve as much as any feeling person would at the plight of an individual polar bear drowning at sea because there is less polar ice. I also acknowledge that some other constituents of the polar bear's habitat will be adversely affected by the extinction of polar bears, and that this is grounds for grief too. And even on an entirely self-interested level, I grieve for a world without polar bears, because they're magnificent, and I get the same kind of pleasure out of contemplating them as you get out of contemplating Christmas Island crabs. But I want to be cautious about this last, and about what we would be prepared to exchange in order to preserve a species for the sake of human pleasure. There are cases where our efforts to conserve a species work against both the individuals of that species (who are conscripted into captive breeding programs) and against other animals (who are trapped/poisoned/infected with haemorrhagic diseases like the calicivirus). Averting human boredom is not, to my mind, enough of a justification for that kind of incursion on the well-being of individual animals.

Regarding your second point that rapid species migration will reduce diversity: yes it will, in the short term, and as I say above, this is certainly grounds for grief; but will it in the long term? I would argue that with enough time, a species located in different environments will begin to speciate, that Australian-located rabbits, for instance, are in the process of becoming different from European rabbits. We have an example in the rubus or raspberry genus, one of the world's oldest extant genera, which by virtue of long-term habitation in several continents has produced different forms: the Rubus parvifolius, native to Australia, very different to the Rubus idaeus of Europe. The speciation I am talking about is a long term prospect, though, and I don't dispute that rapid anthropogenic species migration is producing a world very different from the world that we know (and love).

Your analogy with cultural traffic is very interesting. I'll refer you to William O'Brien's argument that globalisation processes more often lead to cultural hybridization than homogenisation (see O'Brien, "Exotic Invasions, Nativism, and Ecological Restoration: On the persistence of a contentious debate", <i>Ethics, Place & Environment</i> 9 (2006)).

I'm sure you're right that what are now separate land masses were once upon a time contiguous (or more contiguous). All the same, the probably super-continent (or continents) was huge, and would have comprised some very different environments. Unless you think lizards, say, flashed into being in each corner of that land mass, you have to accept that they migrated. Whether they did so pre- or post- the splintering of that supercontinent doesn't alter the fact that they "invaded" different ecologies.

Thank you for this, Byron. Nowhere do I want to say that mass extinction is unimportant - or in fact anything short of disastrous for the world as we know it.

Thanks, Robert. Yes, I'm standing on the shoulders of some very big giants here. The most obvious one is Charles Darwin. <i>The Origin of Species</i> is one long explanation of how environmental pressures, and indeed extinctions, foster speciation. There's an interesting tension between Darwin's representation of life as constantly evolving and the systems ecology's understanding of nature as tending towards stability. As I'm sure you know, I'm not the first person to observe that tension (see e.g., Josef Keulartz and Cor van der Weele, "Framing and Reframing in Invasion Biology", <i>Configurations</i> 16.1 (2008)).

The argument is also informed by posthumanism, which amongst other things queries the nature/culture opposition (see the Zizek reference for a fascinating instance of posthumanist thinking about anthropogenic climate change).

Thanks for mentioning the acclimatisation movements. In an obvious sense, they advocate the opposite of what people like Tim Flannery in his recent QE advocate, but in another sense - that in which they propound a vision of an ideal nature that can only be achieved through human stewardship - there's a disconcerting overlap.

Thanks, Reuben. This is a good summary of my argument, but although I do argue that anthropogenic change is "natural", I don't claim (I certainly don't mean to claim) that because it is natural it is good, okay, or should just be allowed to run its course. What I do say is that when pressures have been exerted on environments in the past, they have produced differentiations among populations, which have, in the long range, fostered biological diversity across ecosystems. I'm reluctant to say that even these processes were good/okay. Okayness only kicks in with a condition of relative ecological stability that comes about as a result of biodiversity that comes about as a result of environmental change. I'm the first to acknowledge that human activity has catapulted species, en masse, into the instability/extinction phase of the evolutionary process.

Yes, human intervention in the processes of anthropogenic extinction would be just as natural all over again. There's nothing in my article that argues against such interventions, although, as I flag in a comment below, there are instances where the preservation of species comes into conflict with the welfare of individual animals, and these are instances which I believe require consideration not only for the welfare of the members of an endangered species, the welfare of those species understood to be antagonists to the endangered species, and the welfare of other individuals and species threatened by the extinction of the endangered species.

To Fred: thanks for reiterating the points about 1080 and calici virus. I agree that we're not very good at making utiliarian judgements, and as a matter of course disproportionately weight our own interests and the interests of those we most care about. I still think it's worth trying to get a sense of how we can minimise suffering, however imperfect our calculations will be, rather than just throwing that effort out and only considering the welfare of the entities we happen to like. Utilitarians of the Peter Singer school have a pretty basic measure of how to apportion moral consideration: capacity to suffer. So if there's a conflict of interest between a dog and a microbe, the dog wins, the antibiotics are administered -- except that once we start thinking about the complex interrelations in an ecology, we realise that there are never only two parties implicated in any relationship, that the well-being of the dog affects the well-being of everything the dog eats, everything that those that the dog eats eat, etc, etc, etc.

Great article (but of course I'd say that). And I'm grateful for your nuanced account of the ethics. My position is this: a species doesn't have intrinsic value (which doesn't mean we don't value it). Its value resides in the benefits it offers to other constituents of an ecosystem. On the other hand, individual animals from within a species do have intrinsic value, in that they value their own life and so have a value unto themselves. This latter value goes as much for members of an indigenous species as an introduced one.

Thank you, Matthew - many interesting points here. You rightly note that I don't offer any answers for how to arrest species extinction and the destabilisation of ecosystems that results, and you also note that "do nothing", when the issues are so pressing, is a course of the most culpable irresponsibility.

So, an attempt at the beginning of an answer: it is not possible to return this country's ecologies to the way they were before White invasion. There is water where there was not water, desert where there wasn't desert, grassland where there was forest, 20 million humans where there were fewer than 1 million, countless millions of sheep, chickens, rabbits, European honeybees, hectares of wheat, pine forests. Even if we deported the extra humans (like me), unblocked all the dams, etc, even so, the oceans that surround this continent have heated and changed the climatic conditions on land and indigenous species have integrated introduced species into their diets (e.g., the quoll attacking your chickens, or closer to my part of the country, the wedge-tail eagle catching the field mice). Sudden changes - even changes that involve the removal of introduced species - need to be considered in the light of how our ecosystems work now. I think what you're suggesting is that we should therefore work towards ecosystem function rather than restoration of pre-invasion ecologies: if that's the case, then I agree; it's not that I think that's the most ethical course, it's that it's the only possible course that won't lead to a landscape inhospitable to all life for a protracted period. And given that the most dysfunctional landscapes at the moment are the agricultural monocultures, I think that's where we need to begin, with reforming our agricultural practices so that we foster landscapes hospitable to life. That is, biodiverse landscapes, environments that function as ecosystems, in which humans are one of the constituents. (N.B. this is of course permaculture.)

I also agree that we would do well to invest some of the energy that currently goes into thinking through existing "invasive" species to thinking about introducing new species, while being open to the fact that *given that our landscape has already changed*, the extremely careful introduction of additional species can aid in achieving ecosystem health. E.g., I understand the introduction of the cactoblastis to have helped with the control of the prickly pear that you mention, even though the cactoblastis has "invasive" status in other environments.