SEED-GERMINATION PERCENTAGE INCREASES WITH POPULATION-SIZE IN A FRAGMENTED PRAIRIE SPECIES

Laboratory germination percentages were relatively low in small populations of royal catchfly (Silene regia), a perennial prairie plant whose distribution has been severely reduced by habitat fragmentation. Populations with more than 150 individuals had uniformly high (< 85%) germination, whereas smaller populations had great variation within and between populations. Germination percentage was related to the natural log of population size (r = 49, p = .017); in small populations the relationship was linear (r = .37, p = .156). Germination success was unrelated to population isolation. The overall dependence of germination percentage on population size has at least two possible explanations: (1) inbreeding depression in recently reduced populations, manifesting itself in lower fitness of seeds; or (2) increased proportion of inferior geitonogamously produced seed caused by reduced hummingbird visitation and reduced interplant movements in small populations.