Data from: Two focal populations and three regional populations of Sobralia chrysostoma

The dispersal and colonization of plant populations allow species to
occupy novel habitats, migrate, and undergo range shifts in response to
changing environmental factors and, as such, are fundamental ecological
processes for ensuring the long-term persistence of species. Natural
landscape disturbance often generates habitats available for colonization.
Patterns of colonization and population expansion can be inferred from the
levels and partitioning of genetic variation of plant populations with
known disturbance histories, such as recent volcanic eruptions. We sampled
and mapped 496 individuals from two populations of the colonizing
terrestrial orchid, Sobralia chrysostoma, on the 1992 lava flow of Volcán
Arenal in central Costa Rica. We used neutral co-dominant markers to
genotype individuals and estimate population genetic statistics.
 Both populations had high mean levels of genetic diversity (P =
100%; AP = 3.31; He = 0.259) suggesting that the lava flow was colonized
by numerous individuals that likely originated from multiple source
populations. However, significant spatial genetic structure (SGS) was only
present in one population at the smallest distance class (≤ 2 m) and was
low (r = 0.032). That these large and genetically diverse populations had
such low SGS and an absence of SGS respectively is contrary to
expectations and differs significantly from the pattern in Epidendrum
radicans (Orchidaceae), with which S. chrysostoma is growing
sympatrically. Our results suggest that these two populations either
consist primarily of immigrant individuals or that seeds produced in situ
dispersed over longer distances, thereby producing larger seed shadows and
greater overlap of seed shadows.