Feeding behaviour of larval Ambystoma granulosum (Amphibia: Caudata)

Aim: Food availability during the early developmental stages of larval salamanders is a bottleneck for their successful breeding strategies and the conservation of amphibians. Zooplankton based diets allow salamander larvae to choose different prey types based on their size and energy gains. In this study, we quantified the patterns of prey selection and functional responses of Ambystoma granulosum during the larval stages (1 to 8 weeks). Methodology: For the prey selection experiment, we offered a mixture of five crustacean zooplankton (Alona glabra, Ceriodaphnia dubia, Heterocypris incongruens, Simocephalus vetulus and Daphnia pulex). A. glabra, C. dubia and H. incongruens were used as prey for the functional response experiments. Results: There was a direct and linear correlation between the larval length and the gape size during the study period. Prey selectivity by A. granulosum indicated a shift in choice of the crustacean species, where small bodied items (e.g., A. glabra)were selected until the fifth week; during the later weeks, these were replaced by the larger S. vetulus and D. pulex. Functional response curves indicated that the pattern of prey consumption mainly corresponded to type II. Ambystoma granulosum offered C. dubia showed increased prey consumption with increasing larval age. However, when fed A. glabra the consumption increased until the sixth week but declined thereafter. Interpretation: Studies on the feeding ecology of A. granulosum allowed us to understand the quantity and type of prey needed as the larvae grow. The highest prey biomass was consumed by A.granulosum only at the highest offered prey density. Since natural availability of prey in high levels are rare, larval A. granulosum possibly suffers from food deficiency and this in turn may lead to high mortality during early stages.