Nutritional status of tadpole populations of Rana temporaria in the Central Alps (Austria)

S y n o p s i s : The nutritional status of the tadpole populations of Rana temporaria in the Hohen Tauern, Austria was investigated. In only 5 out of 19 populations were large and well fed tadpoles found, whereas those of other populations displayed a small body size and atrophic livers with a depletion of storage products (lipids) and an accumulation of melanomacrophages. These symptoms correlated with tadpole densities, but not with water parameters (pH, conductivity, aluminium), altitude, pond area, or toxicants accumulated in tadpoles. Comparable symptoms were found in the laboratory tadpoles that were fed a low energy diet. This confirmed the assumption that high population densities in small mountain ponds lead to the malnutrition of tadpoles, delayed development, and a small size at metamorphosis. As the period between metamorphosis and the beginning of hibernation is only two months and sometimes even less, underfed froglets may not accumulate sufficient energy to survive the long winter period, which lasts 6-8 months. On the other hand, breeding ponds of R. temporaria at high altitudes are often surrounded by pasture land, which improves the feeding conditions of tadpoles due to the fertilisation of oligotrophic water bodies.