Metapopulation ecology, genetics, and viability of Polygonella basiramia, an endangered plant of Florida scrub

Polygonella basiramia is a rare plant endemic to the naturally patchy, fire-driven Florida scrub ecosystem. I analyzed long-term demographic data using metapopulation approaches to determine how habitat patch properties affect patch occupancy and turnover. P. basiramia inhabits white sand gaps in the rosemary shrub community that itself occurs patchily, allowing me to explicitly consider the scale of metapopulation dynamics. From 1999 to 2002, turnover among 1,210 gaps was 8%/year and dominated by local extinctions. Logistic regression shows that the incidence of P. basiramia within gaps increases in larger, less isolated gaps. The probability of local extinction decreases with increasing gap area. The probability that a vacant gap is colonized rises with gap area and proximity to other occupied gaps. Extinction and colonization of populations within 83 rosemary patch populations occurred more slowly (1%/year, 1989--1999) and responded less to habitat characteristics, as expected if large scale patterns integrate over smaller-scale dynamics.; I also studied genetic diversity and gene flow in this metapopulations across spatial scales. I used Bayesian methods to estimate heterozygosity, nucleotide diversity, FST, Ne, and Nm from 81 polymorphic AFLP markers at the small scale and 102 markers at the large scale. Within-deme heterozygosity was moderate at both scales (Hs = 0.263) and was not correlated with deme age, patch area, or isolation. Population differentiation as measured by FST was low (small scale = 0.140, large scale = 0.046) and decreased with patch age. Patterns of gene flow, genetic structure, and the relatively high amounts of linkage disequilibrium are consistent with the rapid turnover dynamics observed. Opportunistic roadside populations harbor genetic diversity similar to scrub populations making them genetically viable components of the metapopulation.