Print PagePlants have long been appreciated to employ life history strategies for persisting in variable environments. Recently, interest in these strategies has grown with concern that global climate change will increase the variability populations face. To explore the extent of these strategies and evidence that they may aid in maintaining California’s flora under climate change, we examined the germination and dormancy strategies of 200 populations of 40 native annual plant species across California’s natural climate gradient. Specifically, we asked: How common is it for annual plants to have seed banks and temperature cued germination consistent with bet-hedging life history strategies? And does the nature of these “risk aversion” strategies change with climate variability? For each population we determined the size of the persistent seed bank in 2006 using soil collected from each field population. We also collected seeds from individual parents in each population, and tested whether seeds preferentially germinated at 5°, 15° or 27°C. Using these data we tested for statistical relationships between germination rates, seed bank presence, latitude and short- and long-term climate factors.
Results/Conclusions
Despite predictions, we found little evidence for germination temperature preferences in 40% of populations from 75% of species. Also counter to predictions, we found no relationship with germination probability and any tested climate factor or latitude, considering all populations together. There was, however, a significant quadratic relationship between latitude and germination for populations with a 5° germination preference. Fitting with predictions, there was a negative relationship between the probability of detecting a seed bank and total annual rainfall and a positive relationship between seed bank presence and mean maximal temperature. Most striking was our finding that species with a 5° germination preference were significantly more likely to have seed banks in sites with minimum winter temperatures below 5°, while populations with a 15° germination preference were significantly more likely to have seed banks in locations with minimum winter temperatures above 5°C. Counter to predictions, our findings suggest that many species do not have climate-based germination or dormancy strategies for risk aversion. Populations without temperature risk aversion strategies are more likely to be vulnerable to climate-change induced extinction than those with such strategies. Our findings also suggest that temperature-based risk aversion strategies vary extensively across populations of the same species and that species-level analyses of climate-change responses are likely to miss important differences among populations.
