Over at Eco-Evo Evo-Eco, Andrew Hendry proposes “Faith’s Conjecture”: in ecology and evolution, the putative causal relationships underlying observed correlations can always be reversed. He discusses a number of examples, such as gene flow and local adaptation–does gene flow prevent local adaptation, or does local adaptation prevent gene flow? The answer is “yes”.
Another way to put the same point would be to say the feedbacks are ubiquitous. It’s never the case that A causally affects B, but not vice versa.
I find it much easier to think of examples than counterexamples. For instance, I’ve previously argued that causality in ecology does not run exclusively from larger to smaller spatial or organizational scales, but also in the reverse direction (see here and here). The only counterexamples I can think of off the top of my head have to do with associations between biotic and abiotic variables. For instance, think of species-area curves: area causally affects species richness, but not vice-versa. Probably if I thought about it more I could come up with some all-biotic counterexamples. But I do think Faith’s Conjecture has a pretty good batting average as eco-evolutionary generalizations go.
Dynamic Ecology 