Life history theory makes several key predictions regarding reproductive strategies depending on demographic vital rates, particularly the relationship between juvenile and adult survival. Two such predictions concern the optimal time to begin reproducing and whether semelparity or iteroparity is favored. Although a large body of theoretical work has led to a rich set of predictions about when each strategy should be favored, experimental tests are still needed. Species introductions provide excellent opportunities for examining these predictions, because selection pressures can change dramatically between the native and introduced ranges. I explore how variation in vital rates across ranges influences optimal flowering strategies, and then ask how observed life history strategies differ from predicted optima between the native and introduced ranges of the monocarpic perennial Cynoglossum officinale.
I collected demographic data from three sites in Germany (native range) and three sites in Montana (introduced range) across four years. I first used these data to compare vital rates between ranges. I then parameterized integral projection models to calculate population growth rate as a surrogate for fitness to compare flowering strategies within and between ranges.
Results/Conclusions
I found that both survival and growth were higher in the introduced range, where size at flowering was larger and iteroparity much more common than in the native range. The observed and predicted strategies for size at flowering were similar in the native range. However, in the introduced range even though plants flowered at a larger size, the observed size was not as large as the predicted optimum. Iteroparity conferred higher fitness in both ranges, suggesting that severe constraints, potentially specialist herbivores, prevent this strategy from becoming more common in the native range.
