Trophic ontogenetic shifts of the dragonfly Rhionaeschna variegata: the role of larvae as predators and prey in Andean wetland communities

Abstract

Body size strongly influences the type and strength of species interactions. Animals with complex life cycles, such as dragonflies, usually go through different stages that include a variation in body size and may involve shifts in their trophic position in the food web. This investigation analyzes the position of the dragonfly Rhionaeschna variegata in the food web according to its body size in Andean wetland communities of northwestern Patagonia (Argentina). The phenology of R. variegata larvae and their potential intraguild predators were studied in wetlands with different hydroperiods. Under controlled experimental conditions, feeding trials were performed to assess the effect of R. variegata on the survivorship of different types of prey. The effects of cannibalism and intraguild predation on the survivorship of the small larvae of R. variegata were investigated with and without alternative prey as well as different sympatric predators. The phenology of R. variegata and intraguild predators differed among wetlands. The feeding trials showed that R. variegata has a significant effect on the survivorship of invertebrate and vertebrate prey. Cannibalism increased with body size in odonate larvae. The survivorship of small and medium-sized larvae was mainly affected by the presence of larger predators such as belosmatids. The field and experimental data show that the effect of intraguild predation and cannibalism is affected by the cohort dynamics of R. variegata. Body size in R. variegata determines the strength of its interaction with other components of the community.