Bet-hedging theory has long fascinated evolutionary ecologists, because it can explain the occurrence of traits that seem maladaptive. In bet-hedging, organisms sacrifice average fitness for reduced variance in fitness and increased lifetime fitness. We investigated whether bet-hedging theory can explain prolonged dormancy (PD), a life history strategy where perennial plants fail to send up shoots for one or more years. At first glance PD seems maladaptive; why stay belowground while others are growing and reproducing? We tested the hypothesis that PD is a bet-hedging strategy using a 23-year demography study of Astragalus scaphoides. Bet-hedging theory predicts that a population without PD will have higher population growth rate with low environmentally induced variance in vital rates. However, as variance increases, a population with PD should eventually have a higher growth rate. We asked: 1. How does environmental variation affect population growth rate? and 2. How does PD affect population growth rate as environmental variation increases? We conducted stochastic simulations and calculated geometric mean population growth rate (λg) as we manipulated variance in vital rates. We compared simulations of populations with and without PD after removing the transition into PD, while keeping other vital rates constant.
Results/Conclusions As expected, the population with PD fared better as variance increased. However, it took high levels of variation to give the population with PD an advantage in λg. Our results do not support PD being a bet hedging strategy except in unusual circumstances. We will combine this study, with future and ongoing experiments, in order to assess the role of this puzzling stage in plant life history strategies.
