Environmental changes in biodiversity hotspot ecosystems of
South Ecuador: RESPonse and feedback effECTs (FOR2730)

Abstract:

Caterpillar ensembles were sampled on 16 species of shrubs from the family Asteraceae and the genus Piper (Piperaceae) in open and forest habitats in the Andean montane forest zone of southern Ecuador between August 2007 and May 2009. Trophic affiliations of caterpillars to the host plants were confirmed in feeding trials. Overall, species richness of herbivorous caterpillars was high (191 species across all plants), but varied strongly between ensembles associated with different plant species (2–96 lepidopteran species per shrub species). Ensembles on Piper species were characterized by low effective species numbers and high dominance of one or two species of the Geometridae genus Eois Hübner. Low species number and high dominance were also found on latex-bearing Erato polymnioides, whereas ensembles on two other Asteraceae species were far more diverse and less strongly shaped by a few dominant species. The observed diversity patterns fit well to the concept that anti-herbivore defenses of plants are the major factors regulating associated insect ensembles. Local abundance and geographic range of host plants appear to have less influence. Lepidopteran species feeding on Asteraceae were found to be more generalistic than those feeding on Piper species. We conclude that caterpillar ensembles on most, but not all, studied plant species are defined by a small number of dominant species, which usually are narrow host specialists. This pattern was more distinct on Piper shrubs in forest understory, whereas Asteraceae in disturbed habitats had more open caterpillar ensembles.

Abstract:

Caterpillar communities were studied on 16 shrub species from the family Asteraceae and the genus Piper (Piperaceae) in the Andean montane rainforest zone of southern Ecuador. The applied sampling methodology was evaluated and found well suited for sampling of caterpillars, especially with focus on resampling. During standardized sampling, a total of 18890 specimens were collected in 11 field surveys between August 2007 and June 2009. Overall, samples were dominated by gregarious early instars and egg clutches of Altinote dicaeus albofasciata (Nymphalidae) on Erato polymnioides (Asteraceae). Those and all other such groups and egg clutches were downweighted for analyses to their cubic root to balance against their overrepresentation in the data set. Trophic associations of caterpillars were confirmed by feeding trials. A substantial fraction of more than 22% of the encountered caterpillars (and up to 80% on individual shrub species) was found not to be trophically linked to the living biomass of the shrubs themselves (“non-herbivores”), but rather feed on dead leaves and epiphylls. Abundance of nonherbivores differed strongly between the two studied plant families, but was very similar on different shrub species within these families. Abundance of herbivorous caterpillars, to the contrary, differed hardly between plant families, but varied strongly between individual plant species. Herbivores were almost entirely comprised of ectophagous folivores, while florivores (2.3%) and semi-endophagous folivores (leaf rollers and tiers; 6.0%) were unexpectedly rare. Absolute species richness of herbivorous caterpillars was high, with a total of 191 Lepidoptera species on the studied 16 shrub species, but varied up to 40fold between individual plant species. Rarefied species numbers were more similar among plant species, but still showed a 15fold difference between the most species rich and most species poor community. Communities on Piper species were characterized by low effective species numbers (measured as exponential Shannon entropy) and high dominance of one or two species of the Geometridae genus Eois. E. polymnioides featured a similar structure dominated by A. dicaeus albofasciata. Communities on the other two Asteraceae (Ageratina dendroides and Baccharis latifolia), to the contrary, were found to have high effective species numbers and low dominance. In conclusion, while Piper species and E. polymnioides feature caterpillar communities defined by small, predictable sets of core herbivores, these defining sets do not exist for the other two of the studied Asteraceae species. Communities on Piper were also more specialized, with 62.8% of the caterpillar species considered monophagous at plant species level, than on Asteraceae with only 11.6% monophagous species. The observed diversity patterns point mainly to shaping by (chemical) plant-herbivore-defense, while geographic range and local abundance of host plants appear to have only limited and varying influence on the associated caterpillar communities.

Abstract:

We analyzed the suitability of a combined sampling approach ? consisting of visual search and branch-beating ? for quantifying tropical caterpillar communities. Surveys were conducted in the Ecuadorian montane forest zone, with two shrub species from the genus Piper serving as focal targets. We sampled 160 shrubs in the course of four experiments following a standardized sampling protocol. Subsequently each shrub was completely defoliated accompanied by an intensive leaf-by-leaf search, in an effort to extract as close to 100% of all present caterpillars as possible. We analyzed the resulting dataset with regard to completeness, taxonomical bias, and influences of daytime, complexity of shrub structure, or experience of the researcher. The standardized sampling protocol extracted between 50.6% and 71.6% of the caterpillars present on a shrub. A minor taxonomic bias of the sampling protocol was observed, but appears to be of a simple and predictable nature, and is therefore easy to account for. We did not find any significant influences of daytime. Structure and size of shrubs had a strong influence on sampling results with small and simply structured shrubs being sampled most completely, large and complex shrubs most incompletely in our dataset. Researcher experience did not appear to have an influence on the sampling efficiency or taxonomic composition of samples obtained when we compared caterpillars obtained by standardized sampling with those collected by exhaustive leaf-by-leaf search. Comparison of caterpillar sizes revealed however, that inexperienced field assistants tended to overlook large fractions of the smallest caterpillars entirely. We conclude that our standardized combined sampling approach is fairly suitable for studies concerning caterpillar communities, especially when resampling of the same shrub individuals is desired.