Data from: Beta diversity and oligarchic dominance in the tropical Forests of Southern Costa Rica

Recent studies have reported a consistent pattern of strong dominance of a
small subset of tree species in Neotropical forests. These species have
been called ‘hyperdominant’ at large geographical scales and ‘oligarchs’
at regional-landscape scales when being abundant and frequent. Forest
community assembly is shaped by environmental factors and stochastic
processes, but so far the contribution of oligarchic species to the
variation of community composition (i.e. beta diversity) remains poorly
known. To that end, we established 20 1-ha plots, i.e. 5 sites with 4
forest types (ridge, slope and ravine primary forest, and secondary
forest) per site, in humid lowland tropical forests of southwestern Costa
Rica to (1) investigate how community composition responds to differences
in topography, successional stage and distance among plots for different
groups of species (all, oligarch, common and rare/very rare species) and
(2) identify oligarch species characterizing changes in community
composition among forest types. From a total of 485 species of trees,
lianas and palms recorded in this study only 27 species (i.e. 6%) were
nominated as oligarch species. Oligarch species accounted for 37% of all
recorded individuals and were present in at least half of the plots. Plant
community composition significantly differed among forest types, thus
contributing to beta diversity at the landscape-scale. Oligarch species
was the component best explained by geographical and topographic
variables, allowing a confident characterization of the beta diversity
among tropical lowland forest stands.