The effects of tropical rainforest transformation on the trophic structure of canopy Diptera, Formicidae, and parasitoid wasps

In recent decades, rapid agricultural expansion in Indonesia has decimated large proportions of the lowland rainforest, most often through the conversion into oil palm and rubber plantations. This change in land-use has been shown to interfere profoundly with the biodiversity and ecosystem functions of the region, including the structure of food webs. As part of the EFForTS project, this study aims to investigate the impact of different agricultural land-use systems on the trophic position and basal resources of three arboreal arthropod groups occupying intermediate to high trophic levels: Diptera, Formicidae, and parasitoid wasps. With their predatory or omnivore feeding strategy, these groups have the property of integrating resources from different lower trophic levels within a food web. They therefore have the potential to function as indicators for the overall flux of energy throughout trophic systems which could be useful for future studies.

Canopy arthropods were collected by canopy fogging from plots in rainforest, jungle rubber plantations, rubber monocultures, and palm oil monocultures from the ‘Bukit Duabelas’ and ‘Harapan’ landscapes in the Jambi Province. For our study, we first extracted amino acids from pre-sorted, bulked samples of Diptera, Formicidae, and parasitoid wasps from the different land-use types. We will then analyze compound specific isotopes in amino acids (δ13C and δ15N) using a fingerprinting approach. With δ13C values of essential amino acids we will identify basal carbon resources of these three higher level consumers while δ15N values of so-called ‘trophic’ and ‘source’ amino acids will be used to calculate precise trophic position of each group. Together, compound-specific isotopes of amino acids will allow us to trace shifts in trophic structure of these canopy arthropods along a tropical land-use gradient.