Demographic constraints in three populations of Lobelia boykinii : a rare wetland endemic

Knowledge about the factors restricting reproduction in many rare wetland plant species is limited. One such species is Lobelia boykinii. We conducted a study of L. boykinii to determine which factors most influence its reproductive success. We examined the species' breeding system, population dynamics, degree of pollen limitation, importance of sexual versus asexual reproduction, and the role of fungal and herbivore damage on fruit production in three Carolina bay populations in North Carolina. Pollen manipulations revealed that L. boykinii is an obligate outcrosser and that sexual reproduction is pollen-limited. Population size and density, which influence pollinator attraction, can fluctuate greatly over years in the same population. The three populations differed with respects to population size and density, capsule production, vegetative reproduction, and ramet survival, and differences are partially attributable to variation in the degree and timing of herbivory and fungal damage. Herbivory ranged from < 1% to 55% of flowering shoots. Fungal infection decreased fruit production only when it coincided with the period of floral development. Our results indicate that focusing on one ecological factor to prevent extant populations from going extinct is insufficient. Multiple intrinsic and extrinsic factors influence L. boykinii's reproductive success, and populations differ in which factors most strongly influence reproduction. Given this suite of constraints, management strategies should include maintaining as many of the largest remnant populations as possible.