title: Trophic assimilation efficiency markedly increases at higher trophic levels in four-level host-parasitoid food chain.
abstract: Trophic assimilation efficiency (conversion of resource biomass into consumer biomass) is thought to be a limiting factor for food chain length in natural communities. In host-parasitoid systems, which account for the majority of terrestrial consumer interactions, a high trophic assimilation efficiency may be expected at higher trophic levels because of the close match of resource composition of host tissue and the consumer's resource requirements, which would allow for longer food chains. We measured efficiency of biomass transfer along an aphid-primary-secondary-tertiary parasitoid food chain and used stable isotope analysis to confirm trophic levels. We show high efficiency in biomass transfer along the food chain. From the third to the fourth trophic level, the proportion of host biomass transferred was 45%, 65% and 73%, respectively, for three secondary parasitoid species. For two parasitoid species that can act at the fourth and fifth trophic levels, we show markedly increased trophic assimilation efficiencies at the higher trophic level, which increased from 45 to 63% and 73 to 93%, respectively. In common with other food chains, δ(15)N increased with trophic level, with trophic discrimination factors (Δ(15)N) 1.34 and 1.49‰ from primary parasitoids to endoparasitic and ectoparasitic secondary parasitoids, respectively, and 0.78‰ from secondary to tertiary parasitoids. Owing to the extraordinarily high efficiency of hyperparasitoids, cryptic higher trophic levels may exist in host-parasitoid communities, which could alter our understanding of the dynamics and drivers of community structure of these important systems.
authors.affiliation: Centre for Ecology and Conservation College of Life and Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, UK Institute of Ecology and Evolution, University of Bern, Baltzerstrasse 6, Bern 3012, Switzerland d.sanders@exeter.ac.uk.
authors.forename: Dirk
authors.identifier: http://orcid.org/0000-0001-7594-3693
authors.initials: D
authors.lastname: Sanders
authors.affiliation: Institute of Ecology and Evolution, University of Bern, Baltzerstrasse 6, Bern 3012, Switzerland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Moser
authors.affiliation: NERC Life Sciences Mass Spectrometry Facility, Scottish Universities Environmental Research Centre, Rankine Avenue, Scottish Enterprise Technology Park, East Kilbride G75 0QF, UK.
authors.forename: Jason
authors.identifier: http://orcid.org/0000-0001-7594-3693
authors.initials: J
authors.lastname: Newton
authors.affiliation: Centre for Ecology and Conservation College of Life and Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, UK.
authors.forename: F J Frank
authors.initials: FJ
authors.lastname: van Veen
mesh_terms: D000818:Animals; D001042:Aphids / Q000469:parasitology*; D018533:Biomass; D005260:Female; D020387:Food Chain; D006790:Host-Parasite Interactions; D007814:Larva / Q000254:growth & development / Q000469:parasitology / Q000502:physiology; D013557:Switzerland; D014863:Wasps / Q000254:growth & development / Q000469:parasitology* / Q000502:physiology*
keywords: Alloxysta; Coruna clavata; Dendrocerus carpenteri; biomass transfer; mummy parasitoids; stable isotope analysis