Ants on skerries: Lasius assemblages along primary succession

Abstract

The splitting of Lasius niger and the description of a new species, Lasius platythorax (Seifert, 1991), brought about a revision of the relative habitat spectra of the two species, which are fairly clear-cut and well known in Central Europe. On the islands of the Baltic Sea, which depending on size are in early or later stage of primary succession, the identity of the pioneer coloniser species, L. niger, has not been updated. Here, we took nest samples in four main habitats to study the occurrence of the two sibling species, and the hypogaeic L. flavus, along a successional gradient from the smallest islets to larger islands and the mainland. Lasius niger was the pioneer species (the single species of one-species islets), and L. platythorax established itself during later successional stages and outnumbered L. niger in the studied mainland habitats, except shore meadows. We discuss possible reasons why L. platythorax was absent in the earliest successional stages, because on the mainland, it frequently nested in rock crevices on outcrops, a nest site often used by L. niger on smaller islands, but rarely on rock and forest outcrops on the mainland. Lasius flavus co-occurred on part of the small islands with L. niger, which it outnumbered on large islands and the mainland by nest numbers, and habitat and nest-site diversities.