Characterisation (δ13C and δ15N isotopes) of the food webs in a New Zealand stream in the Waitakere Ranges, with emphasis on the trophic level of the endemic frog Leiopelma hochstetteri

Leiopelma hochsletteri, the most widespread of New Zealand's native frogs, is recognised as threatened, and is fully protected by legislation. As a first step to characterise the diet and trophic level of L. hochstetteri within streams in the Waitakere Ranges, Auckland, stable carbon and nitrogen isotope analyses were undertaken on a variety of sympatric terrestrial and aquatic plant and animal species, including adult frogs. These results show that: (1) aquatic and terrestrial food webs are linked by terrestrial inputs into the stream; (2) invertebrate and vertebrate predators separate well into distinct trophic groups, and (3) L. hochstetteri occupies an intermediate trophic position among predators, with a diet, at least as an adult, comprising terrestrial invertebrates. Shortfin eels and banded kokopu are identified as potential predators of L. hochstetteri, but data for rats are inconclusive. These results have important implications for the conservation of New Zealand native frog species and riparian stream habitat.