Vertical stratification and defensive traits of caterpillars against parasitoids in a lowland tropical forest in Cameroon

TL;DR

This study examines how caterpillars and their defenses against parasitoids vary in different layers of a tropical forest in Cameroon.

Contribution

The study reveals how caterpillar defensive traits influence parasitism rates across vertical forest strata.

Findings

Caterpillar diversity peaked in the midstory, while density increased in upper canopy strata.

Aposematic and shelter-building caterpillars had higher parasitism rates than cryptic ones.

Defensive strategies are key indicators of parasitism risk in tropical caterpillars.

Abstract

Insect herbivores and their parasitoids play a crucial role in terrestrial trophic interactions in tropical forests. These interactions occur across the entire vertical gradient of the forest. This study compares how caterpillar communities, and their parasitism rates, vary across vertical strata and between caterpillar defensive strategies in a semi deciduous tropical forest in Nditam, Cameroon. Within a 0.1 ha plot, all trees with a diameter at breast height (DBH) ≥ 5 cm were felled and systematically searched for caterpillars. We divided the entire vertical gradient of the forest into eight, five-metre strata. All caterpillars were assigned to a stratum based on their collection height, reared, identified, and classified into one of three defensive traits: aposematic, cryptic and shelter-building. Caterpillar species richness and diversity showed a midstory peak, whereas density followed the opposite pattern, decreasing in the midstory and then increasing towards the highest strata. This trend was driven by some highly dense shelter-building caterpillars in the upper canopy. Specialisation indices indicated decreasing levels of caterpillar generality with increasing height, a midstory peak in vulnerability, and increasing connectance towards the upper canopy, although the latter was likely driven by decreasing network size. Both aposematic and shelter-building caterpillars had significantly higher parasitism rates than cryptic caterpillars. Our results highlight nuanced changes in caterpillar communities across forest strata and provide evidence that defences strategies are important indicators of parasitism rates in caterpillars and that both aposematic and shelter-building caterpillars could be considered a “safe haven” for parasitoids.

The online version contains supplementary material available at 10.1007/s00442-024-05542-x.

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