Selection in Temporally Variable Environments

Fluctuating selection has proven to be a troublesome topic, one fraught with misconceptions, inaccuracies and exaggerations. The simple clonal population genetic model is misleading, and past interpretations of the lottery model of ecology failed to identify the mechanism promoting coexistence, which experiments show is resource limitation. A common definition of bet-hedging, based on comparing arithmetic and geometric means, is criticized. Stochastic phenotypic switching as a means to survive abrupt changes in the environment is illustrated using desert annuals and microbial persisters in the presence of antibiotics. Sequential consumption of resources produces endogenously fluctuating environments that can result in competitive exclusion, coexistence and priority effects. Experiments show that an inferior competitor with a short diauxic lag can coexist with a superior competitor with a long diauxic lag. Simulations shows that three populations stably oscillate when competing for three essential resources, and that twelve populations oscillate chaotically when competing for five essential resources. Models require careful parameterization to support more species than there are resources, and mild environmental perturbations cause the communities to collapse to a few competitors.