Theory of plant defensive level: example of process and pitfalls in development of ecological theory

Several hypotheses appear regularly in the literature as explanations for the level of plant defense, i.e. why some plants are so well defended and others are not. These hypotheses include optimal defense, carbon: nutrient balance, growth rate and growth‐differentiation balance. However, there is considerable dissatisfaction with the progress with the plant defense hypotheses. At least part of the dissatisfaction with the hypotheses and research framed by them arises from the nature of the development of theory. Progress toward a mature stage requires attention to how theory develops (e.g. clearly distinguishing between the theoretical domain and the subset that can be tested, establishing criteria of robustness, properly accounting for discrepancies). In addition, part of the dissatisfaction with the development of the theory stems from inadequate approaches, such as failure to identify and test assumptions in experimental designs, confusing the hypotheses and their predictions, choosing a subsystem (e.g. plant age or part) that may be inappropriate for the test, and defaulting to a less precise hypothesis for explanation of the results.