Print PageFitness consequences in seedling survival and reproductive success in relation to seed size and plant density were investigated for four consecutive years on a population of a desert annual plant, Dithyrea californica. Seed size in this system can be readily measured in its natural setting even after the seed has germinated, making our system ideal for the direct evaluation of the fitness consequences of seed size in a natural setting and hence natural selection on seed size in the wild.
Seedling survival was measured in those years where the cohort of seeds had initial conditions for germination but not subsequent rains to fuel growth and reproduction. Remaining mericarps were recovered in time intervals to relate plant survivorship with the size of their parent seeds.
Reproductive success was measured as the number of seeds produced by individuals in the population and then relating it to the size of their parent seeds.
Results/Conclusions
The four consecutive years differed in the amount and timing of precipitation, the primary environmental driver in deserts, allowing us to observe the consequences of seed size on fitness in a variable environment.
Seed size was positively correlated with the survival of seedlings in the face of drought. Bigger seeds are better provisioned with maternal resources that help them survive better.
Seed size and plant density were positively correlated with the number of seeds produced. However, the intensity of selection varied among years.
Our results suggest that temporal environmental variation results in variable selection on seed size, where additive and interactive effects between water availability and plant competition determine the outcome of selection.
