Extinction Risk of Sonoran Desert Annuals Following Potential Changes in Precipitation Regimes
Rapid environmental change can affect both the mean and variability in environmental conditions. Natural selection tends to favour those organisms that best respond to such changes. Here, we consider delayed germination as bet hedging strategies for 10 Sonoran Desert annuals. We use a germination model parameterized with long-term demographic and climate data to explore potential effects of changes in the mean and variance in precipitation on the evolution of germination strategies, as well as the risk of extinction. We then explored the potential for evolutionary rescue in response to these changes. As expected, results indicate that as rainfall declines, or uncertainty in rainfall increases, all species have higher extinction risk (the former being more detrimental). These shifts also increased the benefit of delayed germination. Results also indicate that evolutionary rescue can often occur for small shifts, especially for more variable rainfall regimes, but would not likely save populations experiencing larger environmental changes. Finally, we identified life history traits and functional responses to precipitation that were most strongly correlated to the ability to cope with changes in rainfall and with potential for evolutionary rescue: dormant seed survivorship and, to a smaller degree, chance of reproduction and seed yield sensitivity to precipitation.