Photos from the Field: Phenology of Predation on Insects in a Tropical Forest

Freerk Molleman, Triinu Remmel, and Katerina Sam, (2016). Phenology of Predation on Insects in a Tropical Forest: Temporal Variation in Attack Rate on Dummy Caterpillars. Biotropica, 48: 229–236. doi: 10.1111/btp.12268

In communities of tropical insects, adult abundance tends to fluctuate widely, perhaps in part owing to predator–prey dynamics. Yet, temporal patterns of attack rates in tropical forest habitats have not been studied systematically; the identity of predators of insects in tropical forests is poorly known; and their responses to temporal variation in prey abundance have rarely been explored. We recorded incidence and shape of marks of attacks on dummy caterpillars (proxy of predation rate) in a sub-montane tropical forest in Uganda during a yearlong experiment, and explored correlations with inferred caterpillar abundance. Applying the highest and lowest observed daily attack rates on clay dummies over a realistic duration of the larval stage of butterflies, indicates that the temporal variation in attack rate could cause more than 10-fold temporal variation in caterpillar survival. Inferred predators were almost exclusively invertebrates, and beak marks of birds were very scarce. Attack rates by wasps varied more over time than those of ants. Attack rates on dummies peaked during the two wet seasons, and appeared congruent with inferred peaks in caterpillar density. This suggests (1) a functional response (predators shifting to more abundant resource) or adaptive timed phenology (predators timing activity or breeding to coincide with seasonal peaks in prey abundance) of predators, rather than a numerical response (predator populations increasing following peaks in prey abundance); and (2) that predation would dampen abundance fluctuations of tropical Lepidoptera communities.

A caterpillar dummy glued to an Allophylus leaf. (Photo: Freerk Molleman).

A caterpillar dummy glued to an Allophylus leaf. (Photo: Freerk Molleman).

Having fun with home-made flagging tape (from plastic bags). Mwesige Isaiah and Francis Katuramu Kanywanii wear the skirts, Boniface Balyeganira and Harriet Kesiime are also present. (Photo: Freerk Molleman).

Having fun with home-made flagging tape made from plastic bags. Mwesige Isaiah and Francis Katuramu Kanywanii wear the skirts, Boniface Balyeganira and Harriet Kesiime are also present. (Photo: Freerk Molleman).

Scoring of damages to caterpillars by Mwesige Isaiah, Francis Katuramu Kanywanii , also showing the cardboard tray for dummies that I invented. (Photo: Freerk Molleman).

Scoring of damages to caterpillars by Mwesige Isaiah, Francis Katuramu Kanywanii , also showing the cardboard tray for dummies that the author invented. (Photo: Freerk Molleman).

The dummy caterpillar hidden in understory vegetation. (Photo: Freerk Molleman).

The dummy caterpillar hidden in understory vegetation. (Photo: Freerk Molleman).