Habitat, Size and Distribution of Scandinavian Limnephilid Caddisflies

Abstract

Most lotic Scandinavian limnephilid caddis larvae make cases from mineral particles, while most lentic species in habitats devoid of fish make organic cases. It is suggested that this difference in case making is caused by different predators in different habitats. Thus, because of their constant predation on the entire larval cycle, fish cause lotic caddis species to use energetically expensive mineral cases which leads to small size in these species. Lentic species in habitats devoid of fish make cheap organic cases allowing large size, i.e. a high proportion of the energy assimilated is allocated to tissue growth. By large size, which is reinforced by case enlargement, lentic species may escape to invulnerable size with respect to many birds, which are potential predators during spring and summer. Lentic species are more widely distributed than lotic ones. It is suggested that this is due to the ephemeral character of many lentic habitats causing these species to disperse more than lotic ones. Concurrently, because of relaxed predation in many lentic habitats these are more easily colonized than lotic ones.