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ABSTRACT Theory suggests that the drivers of demographic variation and local adaptation are shared and may feedback on one other. Despite some evidence for these links in controlled settings, the relationship between local adaptation and demography remains largely unexplored in natural conditions. Using 10 years of demographic data and two reciprocal transplant experiments, we tested predictions about the relationship between the magnitude of local adaptation and demographic variation (population growth rates and their elasticities to vital rates) across 10 populations of a well‐studied annual plant. In both years, we found a strong unimodal relationship between mean home‐away local adaptation and stochastic population growth rates. Other predicted links were either weakly or not supported by our data. Our results suggest that declining and rapidly growing populations exhibit reduced local adaptation, potentially due to maladaptation and relaxed selection, respectively. 

Abstract PremiseSeed germination involves risk; post‐germination conditions might not allow survival and reproduction. Variable, stressful environments favor seeds with germination that avoids risk (e.g., germination in conditions predicting success), spreads risk (e.g., dormancy), or escapes risk (e.g., rapid germination). Germination studies often investigate trait correlations with climate features linked to variation in post‐germination reproductive success. Rarely are long‐term records of population reproductive success available. MethodsSupported by demographic and climate monitoring, we analyzed germination in the California winter‐annualClarkia xantianasubsp.xantiana. Sowing seeds of 10 populations across controlled levels of water potential and temperature, we estimated temperature‐specific base water potential for 20% germination, germination time weighted by water potential above base (hydrotime), and a dormancy index (frequency of viable, ungerminated seeds). Mixed‐effects models analyzed responses to (1) temperature, (2) discrete variation in reproductive success (presence or absence of years with zero seed production by a population), and (3) climate covariates, mean winter precipitation and coefficient of variation (CV) of spring precipitation. For six populations, records enabled analysis with a continuous metric of variable reproduction, the CV of per‐capita reproductive success. ResultsPopulations with more variable reproductive success had higher base water potential and dormancy. Higher base water potential and faster germination occurred at warmer experimental temperatures and in seeds of populations with wetter winters. ConclusionsGeographic variation in seed germination in this species suggests local adaptation to demographic risk and rainfall. High base water potential and dormancy may concentrate germination in years likely to allow reproduction, while spreading risk among years. 

Abstract PremiseSeed germination involves risk; post‐germination conditions might not allow survival and reproduction. Variable, stressful environments favor seeds with germination that avoids risk (e.g., germination in conditions predicting success), spreads risk (e.g., dormancy), or escapes risk (e.g., rapid germination). Germination studies often investigate trait correlations with climate features linked to variation in post‐germination reproductive success. Rarely are long‐term records of population reproductive success available. MethodsSupported by demographic and climate monitoring, we analyzed germination in the California winter‐annualClarkia xantianasubsp.xantiana. Sowing seeds of 10 populations across controlled levels of water potential and temperature, we estimated temperature‐specific base water potential for 20% germination, germination time weighted by water potential above base (hydrotime), and a dormancy index (frequency of viable, ungerminated seeds). Mixed‐effects models analyzed responses to (1) temperature, (2) discrete variation in reproductive success (presence or absence of years with zero seed production by a population), and (3) climate covariates, mean winter precipitation and coefficient of variation (CV) of spring precipitation. For six populations, records enabled analysis with a continuous metric of variable reproduction, the CV of per‐capita reproductive success. ResultsPopulations with more variable reproductive success had higher base water potential and dormancy. Higher base water potential and faster germination occurred at warmer experimental temperatures and in seeds of populations with wetter winters. ConclusionsGeographic variation in seed germination in this species suggests local adaptation to demographic risk and rainfall. High base water potential and dormancy may concentrate germination in years likely to allow reproduction, while spreading risk among years. 

Bet hedging consists of life history strategies that buffer against environmental variability by trading off immediate and long-term fitness. Delayed germination in annual plants is a classic example of bet hedging and is often invoked to explain low germination fractions. We examined whether bet hedging explains low and variable germination fractions among 20 populations of the winter annual plant Clarkia xantiana ssp. xantiana that experience substantial variation in reproductive success among years. Leveraging 15 years of demographic monitoring and 3 years of field germination experiments, we assessed the fitness consequences of seed banks and compared optimal germination fractions from a density-independent bet-hedging model to observed germination fractions. We did not find consistent evidence of bet hedging or the expected trade-off between arithmetic and geometric mean fitness, although delayed germination increased long-term fitness in 7 of 20 populations. Optimal germination fractions were two to five times higher than observed germination fractions, and among-population variation in germination fractions was not correlated with risks across the life cycle. Our comprehensive test suggests that bet hedging is not sufficient to explain the observed germination patterns. Understanding variation in germination strategies will likely require integrating bet hedging with complementary forces shaping the evolution of delayed germination. 

Although the evolution and diversification of flowers is often attributed to pollinator-mediated selection, interactions between co-occurring plant species can alter patterns of selection mediated by pollinators and other agents. The extent to which both floral density and congeneric species richness affect patterns of net and pollinator-mediated selection on multiple co-occurring species in a community is unknown and is likely to depend on whether co-occurring plants experience competition or facilitation for reproduction. We conducted an observational study of selection on four species of Clarkia (Onagraceae) and tested for pollinator-mediated selection on two Clarkia species in communities differing in congeneric species richness and local floral density. When selection varied with community context, selection was generally stronger in communities with fewer species, where local conspecific floral density was higher, and where local heterospecific floral density was lower. These patterns suggest that intraspecific competition at high densities and interspecific competition at low densities may affect the evolution of floral traits. However, selection on floral traits was not pollinator mediated in Clarkia cylindrica or Clarkia xantiana, despite variation in pollinator visitation and the extent of pollen limitation across communities for C. cylindrica. As such, interactions between co-occurring species may alter patterns of selection mediated by abiotic agents of selection. 

1. Spatial partitioning is a classic hypothesis to explain plant species coexistence, but evidence linking local environmental variation to spatial sorting, demography and species' traits is sparse. If co-occurring species' performance is optimized differently along environmental gradients because of trait variation, then spatial variation might facilitate coexistence. 2. We used a system of four naturally co-occurring species of Clarkia (Onagraceae) to ask whether distribution patchiness corresponds to variation in two environmental variables that contribute to hydrological variation. We then reciprocally sowed Clarkia into each patch type and measured demographic rates in the absence of congeneric competition. Species sorted in patches along one or both gradients, and in three of the four species, germination rate in the ‘home’ patch was higher than all other patches. 3. Spatially variable germination resulted in the same three species exhibiting the highest population growth rates in their home patches. 4. Species' trait values related to plant water use, as well as indicators of water stress in home patches, differed among species and corresponded to home patch attributes. However, post-germination survival did not vary among species or between patch types, and fecundity did not vary spatially. 5. Synthesis. Our research demonstrates the likelihood that within-community spatial heterogeneity affects plant species coexistence, and presents novel evidence that differential performance in space is explained by what happens in the germination stage. Despite the seemingly obvious link between adult plant water-use and variation in the environment, our results distinguish the germination stage as important for spatially variable population performance.