Adaptation on Fluctuating Fitness Landscapes: Speciation and the Persistence of Lineages

The NK landscape model of adaptive evolution introduced by Kauffman & Levin (1987) is modified to simulate diversification of monophyletic lineages. Extinction probability is made a function of fitness, and speciation probability a function of the number of fitter one mutant neighbors, which is analogous to genetic potential. Dynamics of adaptive walks are measured as the total number of phenotypically defined species per generation. Changes in species number are described for static and varying landscapes. Persistence of lineages is incompatible with static fitness landscapes and requires that most component species do not reach adaptive optima. Differences in N :K ratios, and therefore in morphological integration, strongly affect speciation rates and could play a role in species sorting.