Beta diversity and oligarchic dominance in the tropical forests of Southern Costa Rica

Abstract

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, that is, five sites with four forest types (ridge, slope and ravine primary forest, and secondary forest) per site, in humid lowland tropical forests of southwestern Costa Rica to (a) 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 (b) 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.Abstract in Spanish is available with online material. K E Y W O R D Sbeta diversity, community composition, neotropical forests, oligarch species, topographic habitats

Moth assemblages in Costa Rica rain forest mirror small‐scale topographic heterogeneity

“…However, the clear majority of our indicator species turned out to be host plant generalists, whereas only 23 species (25%) have taxonomically restricted host plant ranges. Among the few indicator species with narrow larval host ranges (one plant family or even one plant genus), affiliations to Moraceae, Urticaceae ( Cecropia ), or Fabaceae ( Inga ) recurred several times, but we did not recognize any clear patterns in relation to habitat preferences of the more prevalent tree species in the topographic gradients under study (Morera‐Beita et al., ). This tentative survey indicates rather unspecific host–plant associations to predominate among indicator moth species found in the three forest habitat types.…”

“…A foregoing study conducted in the same region reported similarly strong differences in plant community composition among forest plots in relation to topography, successional stage, and disturbance regime (Morera‐Beita et al., ). Based on a subset of the most abundant plant species, especially creek forests exhibited a plant species composition very distinct from forest plots located on ridges and slopes.…”

“…The three forest types under study differed markedly in their floristic composition (Morera‐Beita et al., ; Weissenhofer, Huber, Koukal, et al., ). As expected, this was clearly reflected by differences among moth communities regarding their species composition.…”

“…While a couple of studies have addressed how elevation Beck et al, 2017;Brehm et al, 2016;Fiedler, Brehm, Hilt, Süssenbach & Häuser, 2008) or disturbance gradients (Alonso-Rodríguez, Finegan & Fiedler, 2017;Beck, Schulze, Linsenmair & Fiedler, 2002;Ricketts, Daily, Ehrlich & Fay, 2001) may drive tropical moth diversity, much less is known about small-scale patterns in moth assemblages along orographic gradients. The hilly topography of the Piedras Blancas National Park in SW Costa Rica is characterized by pronounced environmental heterogeneity with different forest habitat types growing under specific environmental conditions (Morera-Beita et al, 2019;Weissenhofer, Huber, Koukal, et al 2008). The aim of the present study was to analyze moth assemblages of three major phylogenetic lineages of Lepidoptera between creek forests (hereafter creek), slope forests (slope), and ridge forests (ridge) in the area.…”

“…(a) For the Golfo Dulce region, several studies reported plant species richness to be higher on ridges compared to slopes and creeks (Hofhansl et al, 2014;Morera-Beita et al, 2019;Weissenhofer, Huber, Koukal, et al, 2008). Higher plant species richness could promote species richness of herbivorous insects because a wider variety of larval host plant species are available and therefore a greater number of herbivore species with different ecological requirements might be able to coexist (Lewinsohn & Roslin, 2008;Novotný & Weiblen, 2005;Novotný et al, 2006).…”