In ecology, species can mitigate their extinction risks in uncertain environments by diversifying individual phenotypes. This observation is quantified by the theory of bet-hedging, which provides a reason for the degree of phenotypic diversity observed even in clonal populations. The theory of bet-hedging in well-mixed populations is rather well developed. However, many species underwent range expansions during their evolutionary history, and the importance of phenotypic diversity in such scenarios still needs to be understood. In this paper, we develop a theory of bet-hedging for populations colonizing new, unknown environments that fluctuate either in space or time. In this case, we find that bet-hedging is a more favorable strategy than in well-mixed populations. For slow rates of variation, temporal and spatial fluctuations lead to different outcomes. In spatially fluctuating environments, bet-hedging is favored compared to temporally fluctuating environments. In the limit of frequent environmental variation, no opportunity for bet-hedging exists, regardless of the nature of the environmental fluctuations. For the same model, bet-hedging is never an advantageous strategy in the well-mixed case, supporting the view that range expansions strongly promote diversification. These conclusions are robust against stochasticity induced by finite population sizes. Our findings shed light on the importance of phenotypic heterogeneity in range expansions, paving the way to novel approaches to understand how biodiversity emerges and is maintained.
Author summaryEcological populations are often exposed to unpredictable and variable environmental 1 conditions. A number of strategies have evolved to cope with such uncertainty. One of 2 them is stochastic phenotypic switching, by which some individuals in the community 3 are enabled to tackle adverse conditions, even at the price of reducing overall growth in 4 the short term. In this paper, we study the effectiveness of these "bet-hedging" 5 strategies for a population in the process of colonizing new territory. We show that 6 bet-hedging is more advantageous when the environment varies spatially rather than 7 temporally, and infrequently rather than frequently. 8 Introduction 9The dynamics and evolutionary history of many biological species, from bacteria to 10 humans, are characterized by invasions and expansions into new territory. The 11 September 19, 2018 1/15 effectiveness of such expansions is crucial in determining the ecological range and 12 therefore the success of a species. A large body of observational [1, 2] and 13 experimental [3-6] literature indicates that evolution and selection of species undergoing 14 range expansions can be dramatically different from that of other species resident in a 15 fixed habitat. Theoretical studies of range expansions based on the Fisher-Kolmogorov 16 equation [7, 8] or variants [9, 10] also support this idea. Adaptive dispersal strategies [2] 17and small population sizes at the edges of expanding fronts [11,12] are among the m...