Demographic, developmental and life-history variation across altitude in Erysimum capitatum

1. Natural variation in life history provides the opportunity to examine its correlated population performance. Alpine systems are considered to be vulnerable to climate change as high-altitude conditions are predicted to become more similar to those at low altitude. Comparing natural populations that exhibit variation in life history across altitude can provide information on how life history may influence the demography of alpine plants under a range of altitudinally or climatically variable conditions. 2. We compared the abundance, demography, life history and morphological development of Erysimum capitatum populations in alpine and lower-altitude habitats in the Colorado Rocky Mountains. 3. Mortality of all life stages was higher at lower elevation than in alpine sites, and low-elevation plants reproduced more quickly and expressed a semelparous life history more frequently than did alpine plants. Significant variation in post-reproductive survival, i.e. the opportunity for iteroparity, was also found across regions. 4. Several life stages contributed comparably to projected population growth in high-altitude, iteroparous populations, whereas low-elevation semelparous populations depended primarily on seedling recruitment and rapid reproductive maturation for population maintenance. Populations with intermediate levels of iteroparity differed from each other in their demography, suggesting that transitional states between iteroparity and semelparity are unpredictable. 5. Morphological development also differed between iteroparous and semelparous plants, with iteroparous plants producingmore vegetative rosettes andmaintaining those rosettes in a vegetative state more frequently than semelparous plants. Sites with lower soil water content were more semelparous. 6. Synthesis. These combined results suggest that changes in developmental rates and morphology may promote changes in fundamental life history. Altitudinal variation inmorphology and parity is strongly associated with demographic variation across altitude, indicating that plastic or evolutionary changes in these traits would influence population performance across altitudinally or climatically variable conditions.