Okay, I've taken the bait - or at least, I'm nibbling at it. Earlier today Jim Crants pretty accurately summarized the points I made off-list, for which I thank him. Here I'm responding to his paragraph regarding 'moral grounds' and to his numbered paragraphs (1-4). In order to minimize repeated replies, I've deleted previous material, leaving only specifically relevant passages. I apologize for the inconvenience of having to look up the rest, but it's probably still in your inbox.
JC: Initially, my argument was on moral grounds: whatever negative effects invasive species have on native species are the fault of our species (unless a non-human disperser was responsible for the intial long-distance-dispersal event, which very rarely happens), and, as moral agents, we are obligated to try to undo or mitigate the harm we cause to others. That's my Catholic upbringing speaking, I guess, and it's apparently not a compelling argument to someone who hasn't already reached the same moral conclusion on exotic invasives. MC: I think it's safe to assume many or most ecologists feel similarly duty-bound, regardless of their particular religious or ethical training. I suspect (but cannot bring data to bear) that (again) many or most of us now active became ecologists partly because we were already convinced that ethics extend beyond human-human interactions. As a child of the 60s and 70s, I can say that fits my experience, and seems to apply to almost every ecologist I've talked to. Relatively fewer of us have tried to articulate our moral convictions in ways philosophers or theologians would consider to be 'principled', and in my view none of us have really succeeded. Whatever else we are, we're animals with limited capacities. To be very 60s indeed, 'there's nothing [we] can do that can't be done', and evidently quite a lot we can't do. Still, human activity has reconfigured the biosphere. Topologically, it's like wadding up a map of the Earth so that places once all but completely separated are now in all but direct contact. Every major port city touches every other. Every major airport likewise. It's not just the world we live in, it's the world everything else lives in, too. Fundamentally redrawing the map by creating wholly new 'currents of commerce' while expecting former 'rules' of dispersal to persist seems naive. Either our morals are outdated, or our actions are immoral. But neither has much effect on global commerce, and the distinction doesn't matter to anything else entrained in our wake. JC(1) Exotic species, on average, interact with fewer species than native species, and their interactions are weaker, on average. In particular, they have fewer parasites, pathogens, and predators, counted in either individuals or species. This is especially true of plants, and especially non-crop plants. I suspect, but have not heard, that exotic plants also have fewer mycorrhizal associates than native ones, but I doubt that they have significantly fewer pollinators or dispersers. Meanwhile, back in their native ranges, the same species have the same number of associations as any other native species. MC(1) Natural selection only produces interactions good enough to persist under prevailing conditions; there is no gold standard. By definition, 50% of all species interact with fewer species than average, and 50% of all interactions are weaker than average. Preferring stronger, more complex interactions means preferring more tightly-coupled (and therefore) 'riskier' systems with a higher likelihood of failure. JC(2) Very-long-distance dispersal by humans confers a fitness advantage over very-long-distance dispersal by other agents, on average, for two reasons. First, humans often disperse organisms in groups, such as containers of seeds, shipments of mature plants and animals, or large populations contained in ballast water, allowing them to overcome the Allee effects (lack of mates, inbreeding depression) their populations would face if introduced as one or a few individuals. We also often take pains to maximize the establishment success of organisms we disperse, by shipping healthy, mature plants and animals and propogating them when they arrive, while non-human dispersal agents usually introduce small numbers of organisms, often nowhere near their peak fitness potential (e.g., seeds, spores, starving and dehydrated animals). MC(2). JC appears to be arguing that once rare occurrences are no longer rare. I agree. But I draw the opposite conclusion, because he is arguing that to generate such changes is morally wrong, while I am just saying: when these conditions prevail, long distance dispersal becomes normal. JC(3) Although the population dynamics of invasive species do not differ by what agent introduced them (whether humans brought them, some other agent did, or they evolved in situ), it is ecologically consequential that human activities are generating so many more invasive species than natural processes usually do. Aside from maybe continents or oceans merging through plate tectonics, nothing non-human introduces such a flood of new species to new environments as we humans have in the last several centuries. MC(3). See MC(2). What was once normal is no longer normal. 'Ecologically consequential' in this context is standing in for 'morally consequential'. Ecologically, change is change. JC(4) To arrive at the conclusion that the terms "native" and "exotic" (or "alien") are ecologically meaningless, you must approach the issue this way: if there is no set of criteria by which one can reliably categorize an organism as native or exotic in the absence of historical evidence, the distinction is meaningless. I think the valid approach is this: if there is no set of criteria by which one can reliably distinguish the category "native species" from the category "exotic species" (*after* the categorization is done based on geographic history), the distinction is meaningless. By analogy, the first approach is like saying that there is no difference in height between men and women because one cannot reliably identify the height of a person by their sex, while the second approach is like saying that there is a difference in height between men and women because men are, on average, significantly taller than women. MC(4). JC undermines his argument here by trying to make the difference between natives and aliens morally inconsequential. I think we can assume that he sees no moral imperative emerging from the statistical likelihood that men are (and have been) taller than women. But we know he believes a moral imperative emerges from the claims he makes in (1-3). So his analogy isn't really an analogy. A better analogy would be a claim that men are, on average, more politically powerful than women, evaluated in light of a moral claim that no such difference should exist. But even that analogy would only recommend equalizing average fitness; leveling the playing field. And it flies in the face of the "past = desired future" formula inherent in anti-alien sentiment. Finally, if Williamson's legendary '10s' rule is even remotely accurate, the aliens are already disadvantaged by multiple orders of magnitude. Long distance transport is now vastly more likely, but establishment at the other end is still a long shot. Matthew K Chew Assistant Research Professor Arizona State University School of Life Sciences ASU Center for Biology & Society PO Box 873301 Tempe, AZ 85287-3301 USA Tel 480.965.8422 Fax 480.965.8330 mc...@asu.edu or anek...@gmail.com http://cbs.asu.edu/people/profiles/chew.php http://asu.academia.edu/MattChew > > > >
