Seasonal climate drives population growth but not costs of reproduction of a perennial wildflower

Costs of reproduction are predicted to shift under climate change, but the extent to which weaker or stronger costs influence population responses to interannual climate variation is unknown. We asked how seasonal climate, manipulated rainfall, and costs of reproduction influence vital rates and population growth in a long-lived herbaceous perennial plant, Primula hendersonii, across an ongoing rainfall manipulation experiment in oak savanna of northwestern North America. Simulated drought reduced population growth rates, and vital rates (e.g., probability of flowering, individual growth) responded individualistically to variation in winter, spring, and summer temperatures, although not to variation in seasonal precipitation. However, only warmer spring temperatures were associated with a decline in population growth rates. Although we observed a weak negative effect of past reproduction on growth and future reproduction for large individuals, these costs of reproduction ultimately did not influence population growth. Further, observational and manipulative experiments to detect costs of reproduction suggest subtle differences in cost expression. We show that direct climate drivers had a stronger effect on population growth than indirect changes in costs of reproduction and may be more important for understanding population persistence under climate change.