Schäfer, A. M., F. Schäfer, T. Wagner & U. Sinsch

Carabid predation on Bombina variegata metamorphs: size at and timing of metamorphosis matter. pp. 222-228.

Abstract. The potential impact of carabid predation on dispersing Bombina variegata metamorphs was studied in the field at the Schmidtenhöhe (Rhineland-Palatinate, Germany) and performing experimental trials in the laboratory. At least four carabid species were demonstrated to feed on metamorphs, with Carabus violaceus and Pterostichus niger mainly preying
on the smallest individuals, and Abax parallelepipedus and Harpalus rufipes indiscriminately attacking smaller and larger individuals. Predation rates were mostly low (5–15% of metamorphs) despite of high prey densities (83 metamorphs per m²), but hungry beetles consumed up to 60% within five days. Plasticity in the timing of metamorphosis (about two months) and in the size at metamorphosis (11–19 mm) observed in the field seemed to reflect mainly the variability in the spawning date and of aquatic environment during the tadpole development. Still, the tendency of metamorphs to be become larger on average towards the end of the metamorphosis period reduced their risk of being predated because the abundance of potential carabid predators did neither vary among habitat types crossed by dispersing metamorphs nor during the period of metamorphosis. Consequently, informed conservation management of endangered B. variegata populations should focus on larval habitats producing large-sized metamorphs to reduce loss of metamorphs by size-assortative carabid predation.

Key words. Amphibia, Anura, Insecta, Coleoptera, Abax parallelepipedus, Carabus violaceus, Pterostichus niger, Harpalus rufipes, size-assortative mortality.