Fig. 2

Choice of modelling according to the competing timescales. When the timescale of each of the dynamics corresponding to X_w, X_u and X_d is well-defined, as is the case with exponential distributions, models 4, 5 and 6 may be approached by the simpler models 1, 2 and 3. The regions where those approximations are valid are indicated on panel (a) for model 4, and on panel (b) for models 5 and 6. Panel (c) depicts a representative evolution over time of the state of the edges, in the four regimes corresponding to the corners of the domains of panels (a) and (b). This qualitative idea of equivalence between models is revisited more rigorously in Fig. 4