Relationships Among Population Size, Environmental Factors, and Reproduction in Lupinus perennis (Fabaceae)

Abstract

Wild Lupine (Lupinus perennis) is an indicator of Midwestern U.S.A. oak savannas and the main larval food for endangered Karner Blue butterflies. In the past 100 y, this perennial has declined in distribution and abundance. To determine if this decline was related to population size and/or environmental factors and to better understand patterns of reproduction, we compared frequencies of seed coat colors, seed production variables, and environmental factors among 16 populations ranging in size from 25 to 8300 plants. Seedlings were germinated in the greenhouse to measure early offspring vigor. A seed color/substrate field experiment examined differences in seed removal to look at predation risk. Higher seed production was associated with increased population size, while fewer seeds per fruit were associated with increased bare ground, and higher fruits per stem and seed mass were found as soil pH increased. Although seedling emergence declined with increased bare ground, seedling growth was most correlated with pH and light, but not population size. Small populations had reduced seed color variation. Seed removal rates averaged 65% across all treatments, but dark-colored seeds had higher predation than light-colored seeds, regardless of substrate. Seed removal increased over time and was influenced by vegetative cover and distance to roads and water. Our results suggest managers should minimize the amount of bare ground and strive to maintain population sizes over 500 in order to restore and conserve Lupine populations.