ABSTRACT
It was noted in Chapter 7 that one of the earlier formal estimates of the size of an ideal population required to prevent drift and inbreeding is often referred to as the Franklin/Soulé 50/500 rule: for the average species an ideal effective population size, Ne, of at least 50 individuals is needed to prevent inbreeding (or inbreeding depression) and 500 individuals to prevent random genetic drift (e.g., see Avise 1994; Meffe 1996: 53; Finkeldey and Hattemer 2007: 123-127). We emphasize that these numbers refer to the ideal effective population size, not the actual population census size. In later analyses including the effects of the accumulation of mutations, Lynch et al. (1995) suggested that Ne sizes should not drop below 100 (and census sizes less than 1,000), and Lande (1995) recommended Ne should not decline below 5,000, to prevent population extinction. Lynch et al. argue that management policies that maintain populations at 100-1,000 census individuals are inadequate, and Schultz and Lynch (1997) suggest that long-term effective population sizes of a few hundred individuals are advisable to prevent population extinction.
