RESEARCH ARTICLE Progressive vegetation succession of fen habitats promotes the lack of habitat specialist ants J. Bujan 1 • A. Brigic´ 2 • Z. Sedlar 3 • R. S ˇ osˇtaric´ 3 Received: 10 March 2015 / Revised: 7 May 2015 / Accepted: 9 June 2015 / Published online: 8 July 2015 Ó International Union for the Study of Social Insects (IUSSI) 2015 Abstract Vegetation succession, drainage, and climate change are causes of peatland habitat loss in the Western Balkans. Ants (Hymenoptera: Formicidae) are one of the most ecologically important invertebrate taxa in terrestrial ecosystems. To explore whether, and to what extent, fen ant communities are specialized, we sampled an alkaline fen, adjacent habitats undergoing vegetation succession, and the surrounding beech forest in west-central Croatia. Here, we show how a fen and its surrounding habitats differ in ant community structure, and which of the environmental variables (soil temperature, moisture, and pH) have the strongest impact in shaping those communities. In the two growing seasons of sampling we recorded 16 ant species, none of which were peatland specialists. While species richness did not differ between the sites, species diversity was the highest at a succession site. Specific environmental conditions of the fen limit colony establishment and allow survival of a small subset of ant species from the sur- rounding habitats. Consequently, only two ant species (Myrmica rubra and Lasius platythorax) were abundant at the fen site. Their presence at other study sites indicates that the fen fauna is composed of generalist species. The fen and forest community composition differed from the succes- sional sites, and it was most strongly affected by soil pH. The fauna of these habitat islands completely lacks peat- land-specific ant species. Knowing more about communities of these disappearing habitats will help us predict future biodiversity losses in similar habitats threatened by vege- tation succession. Keywords Croatia  Balkan  Formicidae  Hymenoptera  Peatlands  pH  Tyrphobiontic Introduction Peatland habitats are widespread in North and Central Europe, whereas in the Western Balkans they comprise small and exceedingly isolated areas (Horvat 1939; Mon- tanarella et al. 2006; Lazarevic´ 2013). Throughout Europe peatlands are increasingly endangered habitat types (Spitzer and Danks 2006; Minayeva et al. 2009). In the Western Balkans they are critically endangered due to abandonment of traditional human activities, drainage, climate change, and vegetation succession (Topic´ and Stancˇic´ 2006). Peatlands in Croatia are disjunct patches of peatland habitats formed during, or immediately after, the last period of glaciation when low temperatures and high humidity enabled dispersal of peatland vegetation further south (Horvat 1950). We know that they were once widespread in the Western Balkans because peat deposits were found beneath agricultural fields (Topic´ and Stancˇic´ 2006). Due to their special hydrology and soil properties, peat- lands usually divide two distinct types: alkaline fens and acidic peat bogs (Spitzer and Danks 2006). Fens are in general minerotrophic peatlands which are supplied with water and nutrients from the ground water, and their soil pH is basic or at least neutral (Rydin and Jeglum 2006). Peat & J. Bujan jelena.bujan@ou.edu 1 Department of Biology, Graduate Program in Ecology and Evolutionary Biology, University of Oklahoma, 730 Van Vleet Oval, Norman, OK, USA 2 Department of Zoology, Faculty of Science, University of Zagreb, Rooseveltov Trg 6, 10000 Zagreb, Croatia 3 Department of Botany, Faculty of Science, University of Zagreb, Marulic´ev trg 20, 10000 Zagreb, Croatia Insect. Soc. (2015) 62:415–422 DOI 10.1007/s00040-015-0420-8 Insectes Sociaux 123