Predictably simple: assemblages of caterpillars (Lepidoptera) feeding on rainforest trees in Papua New Guinea

Abstract

Predictability in the composition of tropical assemblages of insect herbivores was studied using a sample of 35,952 caterpillars (Lepidoptera) from 534 species, feeding on 69 woody species from 45 genera and 23 families in a lowland rainforest in Papua New Guinea. Caterpillar assemblages were strongly dominated by a single species (median 48% of individuals and 49% of biomass). They were spatially and temporally constant (median normalized expected species shared (NESS) similarity between assemblages from the same host was greater than or equal to 0.85 for three sites 8-17 km apart as well as for three four-month periods of the year). Further, the median presence of species was 11 months per year. Assemblages on hosts from different families and genera were virtually disjunct (NESS similarity less than 0.05) as the caterpillars were mostly specialized to a single plant family (77% of species) and, within families, to a single genus (66% of species), while capable of feeding on multiple congeneric hosts (89% of species). The dominance of caterpillar assemblages by a small number of specialized species, which also exhibited low spatial and temporal variability, permitted robust and reliable estimates of assemblage composition and between-assemblage similarity from small samples, typically less than 300 individuals per host plant. By contrast, even considerably larger samples were insufficient for estimates of species richness. A sample of 300 individuals was typically obtained from 1,050 m(2) of foliage sampled during 596 tree inspections (i.e. a particular tree sampled at a particular time) in the course of 19 sampling days (median values from 69 assemblages). These results demonstrate that, contrary to some previous suggestions, insect herbivore assemblages in tropical rainforests have a predictable structure and, as such, are amenable to study.

Spatial and temporal variation in community composition of herbivorous insects on Neoboutonia macrocalyx in a primary tropical rain forest

“…The insect communities were strongly dominated by a few abundant species. The same kind of community pattern was found in Papua New Guinea (Novotny et al 2002c). The dominant species Cecidomyiidae sp.…”

Parasitism rate, parasitoid community composition and host specificity on exposed and semi-concealed caterpillars from a tropical rainforest

“…The average annual rainfall in the Madang area is 3,558 mm, with a moderate dry season from July to September and mean air temperature of 26.5°C, which varies little throughout the year (McAlpine et al 1983). The herbivorous insects show little seasonality in the area [median presence of species was reported to be 11 months by Novotny et al (2002)]. All external leaf-feeding Lepidoptera including leaf rollers and leaf tiers (which together make up [95 % of all larval external leaf chewers on site; Novotny et al 2002) were collected by field assistants from a selection of 38 locally common tree species from both early and late stages of forest succession (Leps et al 2001).…”

“…The sampling spanned 4-16 months per tree species during 2002-2004 (see Table S1 for a list of tree species and corresponding sampling effort and sampling period). The variable sampling effort is due to merging of two datasets with identical sampling methods (Novotny et al 2002(Novotny et al , 2007 to maximize overall sample size. The number of tree inspections (a particular tree sampled at a particular time) exceeded 1,000 per tree species for each 1,500 m 2 sampled.…”

Insects on Plants: Diversity of Herbivore Assemblages Revisited

“…These assemblages may represent nonequilibrium stochastic communities; on the other hand, unpredictability can be a sampling artifact, derived from tourist species that do not feed on the sampled hosts and from the large numbers of rare species characteristic of tropical assemblages (Novotny & Basset 2000, Price et al 1995. The latter alternative is supported by higher constancy in tropical vegetation of the species composition and abundance of locally common, feeding herbivores (Novotny et al 2002b). Community assembly rules are amenable 610 LEWINSOHN NOVOTNY BASSET to experimental study in artificially defaunated vegetation (Floren & Linsenmair 1998).…”