title: Unravelling the role of allochthonous aquatic resources to food web structure in a tropical riparian forest.
abstract: The role of matter and energy flow across ecosystem boundaries for the subsidized consumer populations is well known. However, little is known on the effects of allochthonous subsidies on food web structure and trophic niche dimensions of consumers in the tropics. We excluded allochthonous aquatic insects from tropical streams using greenhouse-type exclosures to test the influence of aquatic allochthonous subsidies on the trophic structure and niche dimensions of terrestrial predators using stable isotope methods. In exclosure treatments, abundance and biomass of terrestrial predators, and biomass of phytophages decreased and increased, respectively. Vegetation-living predators were more responsive to allochthonous inputs than those living on the ground. Overall, lower availability of allochthonous inputs did not affect community-wide metrics and niche width of predators. However, the niche width of some spider families had very low overlap between treatments, and others had wider isotopic niches in the control than in the exclusion treatment. Most of the C and N in predators living in control stretches came from aquatic subsidies, and those predators living in the exclusion treatments switched their diets to terrestrial sources, showing a preference of predators for allochthonous subsidies. Our results suggest that allochthonous subsidies are also relevant to tropical fauna living upon vegetation. Moreover, allochthonous resources may amplify the niche dimension of certain predators or considerably change the trophic niche of others. Our study highlights the importance of including modern isotopic tools in elucidating the role of allochthonous resources on the patterns of trophic structure and niche dimensions of consumers from donor ecosystems.
authors.affiliation: Graduate Program in Ecology, Institute of Biology, State University of Campinas (UNICAMP), CP 6109, CEP 13083-970, Campinas, SP, Brazil.
authors.forename: Fátima C
authors.initials: FC
authors.lastname: Recalde
authors.affiliation: Graduate Program in Ecology, Institute of Biology, State University of Campinas (UNICAMP), CP 6109, CEP 13083-970, Campinas, SP, Brazil.
authors.forename: Thaís C
authors.initials: TC
authors.lastname: Postali
authors.affiliation: Department of Animal Biology, Institute of Biology, State University of Campinas (UNICAMP), CP 6109, CEP 13083-970, Campinas, SP, Brazil.
authors.forename: Gustavo Q
authors.initials: GQ
authors.lastname: Romero
mesh_terms: D000818:Animals; D001938:Brazil; D020387:Food Chain; D065928:Forests; D007313:Insecta / Q000502:physiology*; D045483:Rivers; D014329:Tropical Climate
keywords: Bayesian mixing models; SIAR; community-wide metrics; ecosystem boundaries; flux across ecosystems; food web structure; trophic niche dimension; tropical riparian forest; water-land interfaces; δ13C-δ15N biplots