2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/88560Fluctuations in diversity and extinction sizes are discussed and compared for two different, individual-based models of biological coevolution. Both models display power-law distributions for various quantities of evolutionary interest, such as the lifetimes of individual species, the quiet periods between evolutionary upheavals larger than a given cutoff, and the sizes of extinction events. Time series of the diversity and measures of the size of extinctions give rise to flicker noise. Surprisingly, the power-law behaviors of the probability densities of quiet periods in the two models differ, while the distributions of the lifetimes of individual species are the same.7 pages, 5 figuresPopulations and EvolutionStatistical Mechanicstext