In my last post on the value and possible non-existence of “mesocosms,” I closed with a quote from Stommel’s 1963 paper on scale in physical oceanography. Stommel’s point, which I echoed, is that certain natural processes take place on space or time scales that may not be observable or manipulable, at least with our present capabilities. Ecologists often run up against these limits. As I said in the comments, a common response to criticism along these lines goes something like “Yes, I’m aware of that issue, but for obvious practical/logistical reasons we couldn’t do any better. Ecology is hard.”
This may be true, but it isn’t a good argument. Just because a certain experiment–in or out of a mesocosm–is the only one possible doesn’t necessarily mean its worth doing. There are some species, ecological systems, and processes that are just not amenable to mesocosms.
For instance: how would you do an experiment on competition and resource partitioning between breeding Laysan and black-footed albatrosses in a mesocosm? It would need to be three thousand miles wide, which is impractical. But for obvious reasons, nobody would buy the results of an albatross experiment done in practical 50-m enclosures.
This albatrosses-in-cages idea is intentionally stupid, but my sense is that there are cases where experimenters make less extreme versions of similar errors. The ability to do controlled, randomized experiments is great…until the conditions necessary for control start fundamentally changing the characteristics of the system. We should be able to recognize when this is the case, and stop ourselves, before we do the experiment.
An analogy to particle physics may be helpful. Until the Large Hadron Collider was built, physicists couldn’t test for the existence of the Higgs boson. According to the predictions of the Standard Model, the Higgs boson would not appear unless protons were smashed with a certain amount of energy, which was beyond the capabilities of all the existing particle accelerators.
The physicists did not try to do Higgs experiments in the existing accelerators, because it would have been an utter waste of time. To do the experiments, they required a bigger instrument, which required in turn decades of effort from thousands of scientists, technicians, laborers, and engineers. They and their funders thought it was worth it, and made it happen.
If you think a three-thousand-mile enclosure is necessary to really understand albatross foraging, God bless your little heart, and good luck with the grant application (not to mention your IACUC…). A lot of big ecological questions do require big investments, either in long-term observing systems (think satellites, ocean observatories, CalCOFI, NEON, e-bird…) or experimental setups (like the ELA in Canada). Many small-scale experiments are useful, and there are a number of good approaches that can bridge the gap between small-scale experiments and large-scale predictions. But experiments at the wrong scale are just not among them.