In robotics, “uncanny valley” refers to the fact that robots that look and act somewhat human seem creepy. It’s better for them to either look and act not at all like humans, or to look and act exactly like humans. The latter hasn’t yet been achieved as far as I know.
In ecology, theoretical models and microcosm experiments also have an uncanny valley, when they are designed to mimic a particular natural system only in one or two particular respects. In all other respects they are unlike that particular natural system and not intended to mimic it.
I don’t want to cite examples since I don’t want to single anyone out or pick on anyone, so here’s a made-up example that should give you a “search image”. Imagine a protist microcosm experiment purporting to test the effects of phosphorus enrichment on species diversity in lakes. The size and shape of the protist microcosms are chosen so as to mimic the frequency distribution of surface area-to-volume ratios of N. American lakes, and the range of total phosphorus (TP) concentrations used is chosen so as to match the range of TP concentration in N. American lakes. In all other respects, no effort is made to make the microcosms anything like real N. American lakes. The microcosms are kept in a constant environment in the lab, the growth medium is an artificial medium, they only contain algae, bacteria, and bacterivorous protists that were purchased from a biological supply company, etc. But the experiment is described as revealing the effects of enrichment on species diversity in lakes, specifically. As opposed to (or perhaps in addition to) testing some general theoretical hypothesis about enrichment and diversity that might apply in an approximate way to many different systems.
One sometimes sees the same thing in theoretical models. Made up example: a spatially-explicit metacommunity model in which the patch sizes and connectivity are chosen so as to match a particular natural metacommunity. But the species dynamics within patches are described by a Lotka-Volterra competition model of some arbitrarily-chosen number of species, with arbitrary parameter values. And yet the model is discussed as if it explains the observed features of that particular natural metacommunity.
Which seems…odd. At least to me. Those sorts of models and experiments fall in “uncanny valley” for me. Maybe it’s just me, but don’t understand why it’s useful for a model/experiment that’s unlike any particular natural system in most respects to be matched to a particular natural system in one particular respect. Especially since that one respect usually seems to be chosen arbitrarily. In my admittedly-anecdotal experience, there’s never any case made that the one respect in which the model/experiment matches the natural system is the overwhelmingly important one. As in, if you get that bit of the design right, nothing else matters, because that one bit is going to completely dominate the behavior of the model/experiment. I rarely see anyone test whether their modeling or experimental results are sensitive to the realism of the one particular aspect of their model/experiment that’s supposed to be realistic, by including some unrealistic “controls”. And I rarely see anyone test whether their modeling or experimental results are sensitive to the lack of realism of other aspects of their model/experiment.
To be clear, I see an important place for models and experiments that mimic particular natural systems! I’m thinking for instance of the cattle tank experiments on anuran assemblages that folks like my former advisor Peter Morin used to run (e.g., the Mercer Award-winning Morin 1983). Those cattle tanks aren’t exactly like natural ponds in every respect. But they’re enough like natural ponds in enough respects that their results absolutely do give a lot of valid information about the community ecology of anurans in natural ponds. As a second example, think of Dolph Schluter’s (1994) classic experiment using artificial ponds to show that resource competition selects for character displacement in threespine stickleback. Those artificial ponds were, and were intended to be, reasonably representative of the natural ponds first colonized by ancestral threespine stickleback ~10,000 years ago. As a third example, when Meghan assays the virulence of different parasite genotypes in her lab, I’m sure those assays provide valid indices of the virulence of those particular genotypes in nature, even though the lab environment is unlike the natural environment in various respects. As a fourth example, check out this excellent old guest post from Britt Koskella. To return to the uncanny valley analogy, those sorts of studies are like a robot that looks and acts sufficiently human not to creep people out.
Conversely, as I’ve discussed before and won’t repeat here, I see an important place for theoretical models and experiments that test general principles, but that make no attempt to mimic any particular natural system, although they share some features with many natural systems (e.g., protist microcosms exhibit trophic cascades of a strength typical of trophic cascades in nature). Those studies are like robots that make no attempt to look and act human, although they can do some of the things that humans do.* But a model or experiment that carefully matches some particular natural system in one particular respect while not bothering to match that system in any other respect falls between two stools into uncanny valley.**
To be clear, if some feature of your model or experiment has to be chosen arbitrarily (as is often the case for models and experiments that discover and test general principles), the arbitrary choice to mimic some particular natural system isn’t necessarily any worse than any other arbitrary choice. But it’s not any better, either. And it might be worse if it fools you into thinking your experiment is more “realistic” than it really is.
I recognize that there are times when one wants to mimic a natural system in certain particular respects but not others. Schluter (1994) provides an example. In that experiment, Schluter used interspecific hybridization to create a focal population of fish harboring an unnaturally wide range of genetic and phenotypic variation for selection to act on, so as to maximize his chances of detecting selection. Which is fine! Sometimes to get information about how natural systems work, you have to create unnatural conditions.*** But in the cases I’m thinking of, the many mismatches between the model/experiment and the particular natural system of interest aren’t deliberately chosen so as to increase statistical power or test a scientific hypothesis.
I also recognize that it can be a debatable empirical issue whether a model or experiment that’s designed to mimic a particular natural system actually does so sufficiently well in the relevant respects that its results apply to that natural system.
My advice: if you want your model or experiment to test general principles, just go ahead and do that. It’s fine! You don’t need to give your model or experiment a thin veneer of “realism” by matching one particular aspect of it to some particular natural system. Conversely, if you want your model or experiment to give insight into the behavior of some particular natural system, mimicking that natural system in one particular respect probably won’t cut it. And if you want both, the way to do that is to design your model or experiment to match the particular natural system of interest, and then use other approaches and arguments to draw out the broader implications of your system-specific case study (that’s “approach to generality #5” in this list).
I bet this post is going to be controversial. Indeed, I bet at least a few of my friends will seriously disagree. As always, looking forward to your comments. Especially if you think I’m full of it. 🙂
*Which is why criticizing them as “unnatural” or “unrealistic” totally misses the point. That’s like criticizing Robby the Robot for not looking human.
**I tried to work a third metaphor into this sentence but couldn’t quite manage it.
***Many ecologists fail to appreciate this point, in my admittedly-anecdotal experience.