Demographic Consequences of Pollen Limitation and Inbreeding Depression in a Gynodioecious Herb

Abstract

In a gynodioecious plant population, where female and hermaphroditic plants co‐occur, females must produce more seeds or better‐quality offspring than hermaphrodites to be maintained. Further, differences in the magnitude of pollen limitation and inbreeding depression between females and hermaphrodites may affect the relative fitness of the gender morphs and consequently population dynamics. We integrated demographic data into data on pollen limitation and inbreeding depression in a gynodioecious herb. Using a matrix model approach, we then examined the effects of pollen limitation and inbreeding depression on population growth rate and sex ratio. Hermaphrodites tended to contribute more to population growth rates than females. Because of the insensitivity of population growth rates to variation in annual fecundity, pollen limitation of either females or hermaphrodites had a negligible effect on population sex ratio. Inbreeding depression expressed simultaneously in three fitness components of the offspring produced by hermaphrodites reduced stochastic population growth rate and increased female frequency. Given that population growth rates are insensitive to fecundity transitions and that hermaphrodites have moderate selfing rates, our results suggest that inbreeding depression plays a larger role in the maintenance of females in gynodioecious populations than pollen limitation.