Carabid adaptation to a collembolan diet: hunting efficiency and nutritional value

Abstract

1. Collembola are an important potential food source for carnivorous arthropods living on the soil surface. Nevertheless, due to their effective evasive manoeuvres, Collembola are not an easy prey. Several carabid groups, however, have evolved morphological specialisations to overcome this otherwise effective defence strategy. The adaptive value of this specialisation is still unclear, since some generalist carabids also consume collembolans.2. Feeding experiments with the collembolan specialist Notiophilus biguttatus and four generalist carnivorous carabids revealed that the specialised species are more efficient in hunting Collembola than the generalist species.3. A comparison between specialised and generalist carabid species subjected to a pure collembolan diet further suggests that Collembola are only a dietary supplement for generalists: the generalist carnivore Bembidion lampros decreased in weight and had a higher mortality rate when fed exclusively with collembolans.4. Analogously, a third experiment shows that edaphic mites or other non‐collembolan soil arthropods are just a nutritional supplement for N. biguttatus, since mortality increased when they were fed exclusively with these groups. The adaptation toward Collembola as prey, in contrast, does not constrain N. biguttatus, since they even increased in weight when fed with drosophila.5. The enhanced hunting efficiency of N. biguttatus on Collembola compared to generalist species supports the hypothesis that the convergent evolution of mandibles in all collembolan specialist carabids is highly adaptive. The advantage of specialisation most probably is reinforced by the fact that generalist carabids are not real competitors for specialists, due to their poor efficiency in utilising collembolans.