title: Dung beetles in an avian-dominated island ecosystem: feeding and trophic ecology.
abstract: Globally, dung beetles (Scarabaeidae: Scarabaeinae) are linked to many critical ecosystem processes involving the consumption and breakdown of mammal dung. Endemic New Zealand dung beetles (Canthonini) are an anomaly, occurring at high abundance and low diversity on an island archipelago historically lacking terrestrial mammals, except bats, and instead dominated by birds. Have New Zealand's dung beetles evolved to specialise on bird dung or carrion, or have they become broad generalist feeders? We test dietary preferences by analysing nitrogen isotope ratios of wild dung beetles and by performing feeding behaviour observations of captive specimens. We also use nitrogen and carbon stable isotopes to determine if the dung beetle Saphobius edwardsi will consume marine-derived carrion. Nitrogen isotope ratios indicated trophic generalism in Saphobius dung beetles and this was supported by behavioural observations where a broad range of food resources were utilised. Alternative food resource use was further illustrated experimentally by nitrogen and carbon stable isotope signatures of S. edwardsi, where individuals provided with decomposed squid had δ(15)N and δ(13)C values that had shifted toward values associated with marine diet. Our findings suggest that, in the absence of native mammal dung resources, New Zealand dung beetles have evolved a generalist diet of dung and carrion. This may include marine-derived resources, as provided by the seabird colonies present in New Zealand forests before the arrival of humans. This has probably enabled New Zealand dung beetles to persist in indigenous ecosystems despite the decline of native birds and the introduction of many mammal species.
authors: School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, 1142, New Zealand, jamie.stavert@gmail.com.
authors: J R
authors: JR
authors: Stavert
authors: A C
authors: AC
authors: Gaskett
authors: D J
authors: DJ
authors: Scott
authors: J R
authors: JR
authors: Beggs
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000502:physiology*; D002247:Carbon Isotopes / Q000032:analysis; D001517:Coleoptera / Q000502:physiology*; D004032:Diet; D017753:Ecosystem; D005243:Feces / Q000737:chemistry; D005247:Feeding Behavior / Q000502:physiology; D007091:Image Processing, Computer-Assisted; D009520:New Zealand; D009587:Nitrogen Isotopes / Q000032:analysis; D014741:Video Recording
chemical_list: D002247:Carbon Isotopes; D009587:Nitrogen Isotopes