On Repeatability in Ecology

One of the elementary lessons of statistics is that every measurement must be repeatable so that differences or changes in some ecological variable can be interpreted with respect to some ecological or environmental mechanism. So if we count 40 elephants in one year and count 80 in the following year, we know that population abundance has changed and we do not have to consider the possibility that the repeatability of our counting method is so poor that 40 and 80 could refer to the same population size. Both precision and bias come into the discussion at this point. Much of the elaboration of ecological methods involves the attempt to improve the precision of methods such as those for estimating abundance or species richness. There is less discussion of the problem of bias.

The repeatability that is most crucial in forging a solid science is that associated with experiments. We should not simply do an important experiment in a single place and then assume the results apply world-wide. Of course we do this, but we should always remember that this is a gigantic leap of faith. Ecologists are often not willing to repeat critical experiments, in contrast to scientists in chemistry or molecular biology. Part of this reluctance is understandable because the costs associated with many important field experiments is large and funding committees must then judge whether to repeat the old or fund the new. But if we do not repeat the old, we never can discover the limits to our hypotheses or generalizations. Given a limited amount of money, experimental designs often limit the potential generality of the conclusions. Should you have 2 or 4 or 6 replicates? Should you have more replicates and fewer treatment sites or levels of manipulation? When we can, we try one way and then another to see if we get similar results.

A looming issue now is climate change which means that the ecosystem studied in 1980 is possibly rather different than the one you now study in 2014, or the place someone manipulated in 1970 is not the same community you manipulated this year. The worst case scenario would be to find out that you have to do the same experiment every ten years to check if the whole response system has changed. Impossible with current funding levels. How can we develop a robust set of generalizations or ‘theories’ in ecology if the world is changing so that the food webs we so carefully described have now broken down? I am not sure what the answers are to these difficult questions.

And then you pile evolution into this mix and wonder if organisms can change like Donelson et al.’s (2012) tropical reef fish, so that climate changes might be less significant than we currently think, at least for some species. The frustration that ecologists now face over these issues with respect to ecosystem management boils over in many verbal discussions like those on “novel ecosystems” (Hobbs et al. 2014, Aronson et al. 2014) that can be viewed as critical decisions about how to think about environmental change or a discussion about angels on pinheads.

Underlying all of this is the global issue of repeatability, and whether our current perceptions of how to manage ecosystems is sufficiently reliable to sidestep the adaptive management scenarios that seem so useful in theory (Conroy et al. 2011) but are at present rare in practice (Keith et al. 2011). The need for action in conservation biology seems to trump the need for repeatability to test the generalizations on which we base our management recommendations. This need is apparent in all our sciences that affect humans directly. In agriculture we release new varieties of crops with minimal long term studies of their effects on the ecosystem, or we introduce new methods such as no till agriculture without adequate studies of its impacts on soil structure and pest species. This kind of hubris does guarantee long term employment in mitigating adverse consequences, but is perhaps not an optimal way to proceed in environmental management. We cannot follow the Hippocratic Oath in applied ecology because all our management actions create winners and losers, and ‘harm’ then becomes an opinion about how we designate ‘winners’ and ‘losers’. Using social science is one way out of this dilemma, but history gives sparse support for the idea of ‘expert’ opinion for good environmental action.

Aronson, J., Murcia, C., Kattan, G.H., Moreno-Mateos, D., Dixon, K. & Simberloff, D. (2014) The road to confusion is paved with novel ecosystem labels: a reply to Hobbs et al. Trends in Ecology & Evolution, 29, 646-647.

Conroy, M.J., Runge, M.C., Nichols, J.D., Stodola, K.W. & Cooper, R.J. (2011) Conservation in the face of climate change: The roles of alternative models, monitoring, and adaptation in confronting and reducing uncertainty. Biological Conservation, 144, 1204-1213.

Donelson, J.M., Munday, P.L., McCormick, M.I. & Pitcher, C.R. (2012) Rapid transgenerational acclimation of a tropical reef fish to climate change. Nature Climate Change, 2, 30-32.

Hobbs, R.J., Higgs, E.S. & Harris, J.A. (2014) Novel ecosystems: concept or inconvenient reality? A response to Murcia et al. Trends in Ecology & Evolution, 29, 645-646.

Keith, D.A., Martin, T.G., McDonald-Madden, E. & Walters, C. (2011) Uncertainty and adaptive management for biodiversity conservation. Biological Conservation, 144, 1175-1178.

Leave a Reply