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

Abstract

In many tropical lowland rain forests, topographic variation increases environmental heterogeneity, thus contributing to the extraordinary biodiversity of tropical lowland forests. While a growing number of studies have addressed effects of topographic differences on tropical insect communities at regional scales (e.g., along extensive elevational gradients), surprisingly little is known about topographic effects at smaller spatial scales. The present study investigates moth assemblages in a topographically heterogeneous lowland rain forest landscape, at distances of less than a few hundred meters, in the Golfo Dulce region (SW Costa Rica). Three moth lineages—Erebidae–Arctiinae (tiger and lichen moths), the bombycoid complex, and Geometridae (inchworm moths)—were examined by means of automatic light traps in three different forest types: creek forest, slope forest, and ridge forest. Altogether, 6,543 individuals of 419 species were observed. Moth assemblages differed significantly between the three forest types regarding species richness, total abundance, and species composition. Moth richness and abundance increased more than fourfold and eightfold from creek over slope to ridge forest sites. All three taxonomic units showed identical biodiversity patterns, notwithstanding their strong differences in multiple eco‐morphological traits. An indicator species analysis revealed that most species identified as characteristic were associated either with the ridge forest alone or with ridge plus slope forests, but very few with the creek forest. Despite their mobility, local moth assemblages are highly differentially filtered from the same regional species pool. Hence, variation in environmental factors significantly affects assemblages of tropical moth species at small spatial scales. Abstract in Spanish is available with online material.

Trait Variation in Moths Mirrors Small-Scaled Ecological Gradients in A Tropical Forest Landscape

“…A plethora of such studies during the past 2–3 decades have demonstrated that the species composition of these insects usually mirrors environmental gradients at surprisingly high spatial resolution. For example, in two earlier studies conducted in a perhumid tropical landscape in SW Costa Rica [ 5 , 6 ], we have shown that species composition reveals very clear patterns with regard to gradients in terms of land-use intensity and local topography. However, the ecological interpretation of such patterns is often hampered by the fact that for most tropical insect species, even if their taxonomy is reasonably well resolved, we lack information on many relevant life-history traits that would be required for a deeper functional understanding.…”

“…With the degradation of moth faunas in diversity, abundance, and body size, more specialist insectivorous predators lose an important food source, so that food webs in highly disturbed tropical forest systems are seriously modified [ 41 ]. In contrast, although understory density within the closed old-growth forest varies between topographical types [ 6 , 14 ], differences between these forest types were too subtle and the habitat fidelity of most moth species was too limited to measurably influence community-wide moth size within intact rainforests at this small spatial scale.…”

“…Recent research has confirmed the serious effects of oil palm cultivation on biodiversity of the region [ 5 , 17 , 18 , 19 ]. At the same time, there is a substantial variation in ecosystem structure and biota along the topographic gradient inside old-growth forests, even though these sites only span a narrow elevational range of about 100–280 m asl [ 6 , 20 , 21 ].…”

“…The distribution of the 38 sampling sites in the landscape is shown in Figure 1 . Further information on the sites and their moth assemblages can be found in [ 5 , 6 ].…”

Invertebrates and the complexity of tropical ecosystems

“…We touch on several such directions here. Well‐designed comparative approaches comparing ecological patterns across ecological gradients and boundaries produce new and more general insights (see Chatelain, Elias, Guilbert, & Soulier‐Perkins, ; Mottl, Fayle, Yombai, Novotný, & Klimeš, ; Rabl, Gottsberger, Brehm, Hofhansl, & Fiedler, ; Raine, Slade, & Lewis, , all available in this issue). Expanding attention into a wider spread of invertebrate taxa adds insights as a wider range of ecosystem functions is encompassed (see Chatelain et al, , Drinkwater, Williamson, Clare, & Rossiter, , Luke, and Phillips, Chung, Edgecombe, & Ellwood, , all available in this issue). Using the rapid response times of invertebrates in terrestrial ecosystems allows us to evaluate impacts of and recovery from environmental transformations due to natural and human actions (see Franca et al , Luke et al, , Stone, Shoo, Stork, Sheldon, & Catterall, , Torppa, Wirta, & Hanski, , all available in this issue). The availability of effectively limitless computing power potentially allows the enormous complexity of tropical food webs and distribution maps (see Scriven et al, , this issue) to be modeled realistically: Interpreting very complex model systems of course may be as challenging as contemplating the real thing (McLane, Semeniuk, Mcdermid, & Marceau, ). Aligning pattern and process: Does tropical biodiversity matter beyond its intrinsic value? Can ecosystem processes and service survive a massive decline in invertebrate species and density?…”