Several models have been proposed to explain the diversification of life during geological periods. According to Benton (1997), The diversification of marine families in the past 600 million years (Myr) appears to have followed two or three logistic curves, with equilibrium levels that lasted for up to 200 Myr. In contrast, continental organisms clearly show an exponential pattern of diversification, and although it is not clear whether the empirical diversification patterns are real or are artifacts of a poor fossil record, the latter explanation seems unlikely. In this problem, we will investigate three models fordiversification. They are analogous to models for populationgrowth, however, the quantities involved have a differentinterpretation. We denote by N(t) the diversification function,which counts the number of taxa as a function of time, and by rthe intrinsic rate of diversification.

(a) (Exponential Model) This model is described by

(b) (Logistic Growth) This model is described by

(c) Assume that

(d) Use your answer in (c) to explain the following quote from Stanley (1979): There must be a general tendency for calculated values of

(e) Explain why the exponential model is a good approximation to the logistic model when