Support for Baker's law: Facultative self‐fertilization ability decreases pollen limitation in experimental colonization

Abstract

PremiseThe ability to self‐fertilize is predicted to provide an advantage in colonization because a single individual can reproduce and establish a next generation in a new location regardless of the density of mates. While there is theoretical and correlative support for this idea, the strength of mate limitation as a selective agent has not yet been delineated from other factors that can also select for self‐fertilization in colonization of new habitats. We used known mating‐system variation in the American bellflower (Campanula americana) to explore how plants’ ability to self‐fertilize can mitigate density‐dependent reproduction and impact colonization success.MethodsWe created experimental populations of single individuals or a small number of plants to emulate isolated colonization events. These populations were composed of plants that differed in their ability to self‐fertilize. We compared pollen limitation of the single individuals to that of small populations.ResultsExperimental populations of plants that readily self‐fertilize produced consistent seed numbers regardless of population size, whereas plants with lower ability to self‐fertilize had density‐dependent reproduction with greater seed production in small populations than in populations composed of a single individual.ConclusionsWe experimentally isolated the effect of mate limitation in colonization and found that it can select for increased self‐fertilization. We show the benefit of self‐fertilization in colonization, which helps to explain geographic patterns of self‐fertilization and shows support for Baker's law, a long‐held hypothesis in the field of mating‐system evolution.