Trophic identity of Ezo salamander : Cannibalism can temporally elevate the trophic position of larvae

Abstract

Compound-specific stable isotope analysis of amino acids (CSIA-AAs) has increasingly been used in biogeochemical studies as a powerful tool for providing unprecedented accuracy in the understanding of ecological and environmental dynamics in ecosystems. In the present study, we applied this CSIA-AAs for illustrating the trophic identity of Ezo salamander that has ‘cannibalism’ as a life strategy for adapting to the aquatic-terrestrial boundary ecosystems. Ezo salamander has two types of cannibalism: to hasten the timing of metamorphosis, larvae can develop large bodies and broad heads that allow them to gulp down conspecifics (Type I); and, to delay the timing of metamorphosis, larvae feed on the extremities (i.e., limbs and tails) of conspecifics (Type II, not showing morphological development as in Type I). The results of CSIA-AAs for the salamanders in controlled feeding experiments reveal that the trophic elevation of salamanders without the presence of cannibalism is normal (i.e., one level higher than diets) whereas the elevation of salamanders with the presence of cannibalism is higher than one level for both types. Because salamanders (and also other amphibians) play a critical role both as consumers and prey in aquatic-terrestrial boundary ecosystems, a new insight about ‘the extent to which they can alter their trophic identity in response to cannibalism’ in the present study will be useful for better understanding the unique nutrient and energy cycle in transitional environments between aquatic and terrestrial ecosystems.