Phylogeography and Demography of Common Plant Species from the Philippine Islands

Effects of historical and current environmental conditions on plant populations from the Philippine Archipelago are investigated. The complex geologic history of the Philippines creating a diverse and highly endemic flora is reviewed. Apart from tectonic activity, the islands were subjected to changes in topography, temperature, and precipitation from Pleistocene glacial and interglacial periods (Heaney, 1991). Comparative phylogeography is used to determine the effects of Pleistocene events on the population genetic structure of two endemic species, Daemonorops mollis (Arecaccae) and Macaranga bicolor (Euphorbiaceae). Limited variation and the distribution of unique haplotypes in both species suggest that during periods of lowered sea levels, rainforest habitats were maintained as refugia throughout the archipelago. A land barrier between eastern and western Luzon and water surrounding each island restricted dispersal among populations. A potential route of island colonization in the south- and west-ward direction from northeast Luzon was recovered in M. bicolor. An eastern Luzon population was studied to document spatial distributions and species-habitat associations, and determine possible mechanisms facilitating coexistence in species-rich communities. Torus translation tests showed contrasting patterns of stream- and elevation-microhabitat associations between three palm tree species and D. mollis, a liana, suggesting a potential for niche differentiation between growth forms. In 30 dominant tree species, each was associated with at least elevation, slope, or stream at one or more life stages (saplings, juveniles, or adults), but associations varied across life stages in most species. Species sharing a microhabitat are shown to partition the niche, in time if not in space. Distributions at different life stages were also analyzed to infer what processes resulted in the observed spatial patterns. Aggregation was exhibited in all species at multiple scales, and decreased with species abundance and long-distance dispersal. Correlation analyses measured the relationship between clusters of saplings, or juveniles, with clusters of adults or distance to the nearest conspecific adult. Results show greater clustering of saplings around adults in three species, attributed to negative density dependent effects on juveniles. In ten species, juveniles clustered more around adults indicating negative density dependence before the sapling stage, while recruitment into the juvenile stage was successful for saplings located in suitable habitats near adults. Seed dispersal, negative density dependence, and niche differentiation, are therefore important in maintaining the diverse tree community in Palanan, Philippines.