Bet hedging with seed banks

Bet hedging with seed banks

       Bet hedging is an evolutionary response to variable and unpredictable environments (like the desert!).

       We have sayings about bet hedging like, “A bird in the hand is worth two in the bush” or “Don’t put all your eggs in one basket”

                These capture the idea of giving up some potential gain to lower risk in a variable unpredictable environment.

       Desert annual plants bet hedge by holding back a fraction of seeds that do not germinate even when conditions are favorable.

       The greater the year-to-year variation in success in the growing life stage of a desert annual, the stronger the selection to lower the germination fraction and bet hedge with dormant seeds.

       Year-to year variation in reproduction (21 years of Tumamoc data) is driven by variation in growing season rainfall:

Yet species differ in their sensitivity to rainfall variation:

High variance species, which are more sensitive to variation in rainfall, should have lower germination fractions. Our long-term data show that they do:

      

This shows that delayed germination of desert annuals acts as a bet hedging strategy!

For more on bet hedging see:

Venable, D. L. 2007. Bet hedging in a guild of desert annuals. Ecology 88: 1086-1090. pdf

Gremer, J. R., and D. L. Venable. 2014. Bet hedging in desert winter annual plants: optimal germination strategies in a variable environment. Ecology Letters 17:380-387. pdf

Gremer, J. R., Kimball, S., and D. L. Venable. 2016. Within- and among-year germination in Sonoran Desert winter annuals: bet hedging and predictive germination in a variable environment. Ecology Letters 19:1209-1218. pdf