Data from: Effects of population size and isolation on heterosis, mean fitness, and inbreeding depression in a perennial plant

In small isolated populations, genetic drift is expected to increase
chance fixation of partly recessive, mildly deleterious mutations,
reducing mean fitness and inbreeding depression within populations and
increasing heterosis in outcrosses between populations. We estimated
relative effective sizes and migration among populations and compared mean
fitness, heterosis, and inbreeding depression for eight large and eight
small populations of a perennial plant on the basis of fitness of progeny
produced by hand pollinations within and between populations. Migration
was limited, and, consistent with expectations for drift, mean fitness was
68% lower in small populations; heterosis was significantly greater for
small (mean = 70%, SE = 14) than for large populations (mean = 7%, SE =
27); and inbreeding depression was lower, although not significantly so,
in small (mean = )0.29%, SE = 28) than in large (mean = 0.28%, SE = 23)
populations. Genetic drift promotes fixation of deleterious mutations in
small populations, which could threaten their persistence. Limited
migration will exacerbate drift, but data on migration and effective
population sizes in natural populations are scarce. Theory incorporating
realistic vari- ation in population size and patterns of migration could
better predict genetic threats to small population persistence.