Drift compensation in larval European fire salamanders, Salamandra salamandra (Amphibia: Urodela)?

Abstract

Organismic drift in lotic waters can have major impact on population dynamics. It is influenced by a variety of interacting abiotic and biotic factors, and species often have evolved specific strategies for drift avoidance and compensation. We studied downstream and upstream movements of larval fire salamanders (Salamandra salamandra) within three first-order streams in Germany using up- and downstream traps. We tested several predictions related to the influence of body size, water flow and inclination on the number of upstream and downstream moving larvae. Larval fire salamanders actively moved upstream in all creeks, however, in much lower numbers than downstream. The total body lengths of upstream and downstream moving larvae did not differ significantly; in contrast, downstream drifting larvae were smaller compared to non-drifting larvae collected randomly from the creeks in-between traps. There was no negative effect of the amount of water flow on larval upward movements, but significantly more larvae drifted downstream with the increasing water flow volume. There was no effect of inclination on the amount of either upstream or downstream movements. Our results indicate that upstream movements are a side product of a principle rheotactic behaviour, which prevents larvae from being drifted downstream.