Inferring the Dynamics of Diversification: A Coalescent Approach
Schematic illustration of the nine diversification models considered in our analyses. The models can be classified according to three broad criteria: diversity is either expanding over time (in red, Models 3–6) or saturated (Models 1 and 2); rates either vary over time (in blue, Models 2, 4a–4d, and 6) or they are constant over time (Models 1, 3, and 5); and extinctions are either present (in green, Models 1–4) or absent (Models 5 and 6). There are four flavors of models that exhibit expanding diversity with time-varying rates and positive extinction: the speciation rate (λ) varies over time while the extinction rate (μ) is constant (Model 4a); the extinction rate varies over time while the speciation rate is constant (Model 4b); both rates vary over time with a constant extinction fraction (; Model 4c); and both rates vary independently over time (Model 4d). When they vary, rates either decay or grow exponentially. The parameters of each model are shown in Table 1.