Bet Hedging over Growth and Survival under Demographic Fluctuations*

The growth of biological populations is subject to stochastic fluctuations in the birth and death processes of individuals. Such demographic fluctuations create a trade-off between growth and survival for small populations. During biological dispersal, for example, the survival of newly founded populations may be as important as the growth of already established populations. Using a statistical physics model of birth, death, and migration processes, we show that the expansion rate of a species' overall abundance can be maximized by a bet-hedging strategy, in which the population constantly diversifies into subpopulations of “fast-growing” and “better-surviving” individuals. A similar bet-hedging strategy has previously been suggested as a defense mechanism against environmental variations. We unify those bet-hedging strategies against demographic and environmental variations as a general means of adaptation to both types of uncertainties in population growth.