Natural populations are always fluctuating in size, and we’d like to infer from the pattern of fluctuations something about the underlying ecological mechanisms driving them. Oikos recently published a nice piece of handwaving from Graham Bell. In case there was any doubt, I really do mean it as a complement when I call Mathew and Jon great hand wavers, although I suspect they may not think of themselves in that way.) (UPDATE: Jon responds by saying ‘Thanks…I think’. No, I’m not going to tell you who I think the bad hand wavers are… They’re really good at using simple, equilibrial food web models with just 2-4 species to think about complex phenomena like turnover in species richness and composition along natural environmental gradients. Mathew Leibold and Jon Chase are great hand wavers. I think that some ecologists definitely are better at hand waving than others. But just because hand waving involves judgment calls doesn’t mean there aren’t better and worse hand waving arguments (much like there are better and worse judges). There’s an art as well as a science to hand waving. So hand waving arguments always involve some judgment calls. Of course, there are no hard and fast rules about what’s a good (or good-enough) approximation, or what’s an essential vs. If Ed were stranded on a desert island, I doubt he’d wave his arms to attract a passing ship (which brings us back to the point that sometimes arm waving is a good thing, such as when the alternative is to be stranded).Įd and I are of course not the only ones to get a chuckle out of hand waving: This was certainly true in the case of Ed, one of the world’s best and most rigorous population ecologists. In contrast, the best population ecology involves tight, rigorous connections between theory and data population ecologists hold their arms stiff at their sides like Irish step dancers. My former colleague Ed McCauley and I used to joke that community ecology consists of theory on one side, data on the other, and a bunch of community ecologists in the middle frantically waving their arms (arm waving being a more extreme form of hand waving). At least, that’s the perception of community ecology I wouldn’t venture to guess at how true the perception is, though I’m not above joking about it. Hand waving arguments are perhaps especially common in community ecology, where our theoretical models typically are much simpler than the natural communities to which they’re applied (although not inevitably so, as I’ve discussed in a previous post). A model with no simplifying assumptions would be like a map as big as the world itself, and equally useless. Simplifying assumptions are a feature, not a bug, a point well-articulated by philosopher Bill Wimsatt and in an ecological context by Hal Caswell. false) assumptions, all models are in a sense hand waving arguments about what the real world might be like. Indeed, since all models (mathematical and otherwise) have simplifying (i.e. (What it means to ‘capture the essence’, and how it’s different from, say, ‘getting the right answer for the wrong reasons’, is a subject for another post…) The hope is that the simple model somehow ‘captures the essence’ of the complex situation. I’d also include rigorous models of simple situations which can, via hand waving arguments, be used to develop hypotheses about, or interpret data from, more complex situations. Hand waving can include heuristic arguments, approximations, and rough ‘back of the envelope’ calculations. In order to make progress, we are often faced with a choice, not between a rigorous argument and a hand waving argument, but between a hand waving argument and no argument at all. Ecology is hard, and hand waving makes it easier. More interestingly, there can be substantive reasons for hand waving (and the line between presentational and substantive hand waving isn’t clear cut). For instance, presentational reasons: the time constraints of a seminar often oblige the speaker to gloss over technical details. But there are often good reasons for such lack of rigor. If by hand waving we simply mean omitting assumptions or steps in an argument for no good reason (or worse, for a bad reason, such as the desire to mislead the audience), then yes, hand waving is bad. ‘ Hand waving‘ in science has a bad reputation referring to an argument as ‘hand waving’ suggests a lack of rigor.
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