RESEARCH ARTICLE River islands as habitats for soil mites (Acari) Katarzyna Faleńczyk‐Koziróg 1 | Piotr Skubała 2 | Michał Habel 3 | Barbara Waldon‐Rudzionek 4 | Dawid Szatten 3 1 Department of Evolutionary Biology, Kazimierz Wielki University in Bydgoszcz, Bydgoszcz, Poland 2 Department of Ecology, Faculty of Biology and Environmental Protection, University of Silesia, Katowice, Poland 3 Institute of Geography, Kazimierz Wielki University in Bydgoszcz, Bydgoszcz, Poland 4 Department of Botany, Kazimierz Wielki University in Bydgoszcz, Bydgoszcz, Poland Correspondence K. Faleńczyk‐Koziróg, Department of Evolutionary Biology, Kazimierz Wielki University in Bydgoszcz, Chodkiewicza 30, Bydgoszcz 85‐064, Poland. Email: kasia.fk@ukw.edu.pl Funding information Polish National Science Centre (NCN), Grant/ Award Number: DEC‐2017/01/X/NZ8/00170 Abstract River islands are a natural element of fluvial river systems. They are the refuge of many species of plants and animals and of unchanged ecological systems. Due to their spatial isolation, river islands are good places to observe colonization processes of both flora and fauna (biota). The goal of our research was to observe the develop- ment of soil mite communities colonizing the river island. Mite communities on river islands are dominated by eurytopic species, which are r‐strategists, reproduce parthe- nogenetically, and can be dispersed either passively by the wind or actively by phoresis on insects, small mammals, or birds. The main factors limiting the diversity of acarofauna on river islands are floods (and the resulting soil moisture content of the environment) and spatial isolation. The fertility of the habitat (content of humus) is of less importance. The results of our research indicate that Oribatida are the most sensitive to frequent flooding and high soil moisture, and they were the least effective in colonizing the island. Among the species resistant to the above‐ mentioned limiting factors were Cheiroseius borealis, Cheiroseius bryophillus, Cheiroseius curtipes, Liochthonius lapponicus, Punctoribates punctum, Arctoseius cetratus, Parasitus beta, Ameroseius corbicula, Oribatula tibialis, Tectocepheus velatus, and representatives of Acarididae, Pygmephoridae, Stigmeidae, and Tarsonemidae. KEYWORDS Astigmata, colonization, flooding, Mesostigmata, Oribatida, Prostigmata, river valleys 1 | INTRODUCTION River valleys are among the most diverse and variable terrestrial hab- itats, offering a wide range of ecological niches (Ballinger, Mac Nally, & Lake, 2005; Hendrickson, 2014; Vanbergen et al., 2017). One of the elements of river valleys is river islands, which are characterized by high isolation, environmental integrity, and constant contact with the aquatic environment (Bridge, 2003). They are an element of the natu- ral evolution of fluvial river systems (Allan, 1995). Both the islands and the whole river valley are highly dynamic environments because of the hydrogeomorphological processes occurring and the episodic distur- bances caused by flood waters (Bayley, 1995; Junk, Bayley, & Sparks, 1989; Tockner, Malard, & Ward, 2000). The latter can disorganise the structure of both plant and animal communities (e.g., Bonn, Hagen, & Wohlgemuth‐von Reiche, 2002; Burkart, 2001; Fournier, Gillet, Le Bayon, Mitchell, & Moretti, 2015; Lessel, Marx, & Eisenbeis, 2011). River islands, especially those located in the central part of a river- bed, due to their isolation can be used to track processes such as soil formation, colonization through pioneering plants, initiation of plant communities, and settlement of emerging ecological niches by fauna. The processes of river island formation and their colonization by veg- etation and fauna such as millipedes, carabid beetles, spiders, turtles, or birds are relatively well documented (e.g., Corenblit, Tabacchi, Steiger, & Gurnell, 2007; Gurnell et al., 2001; Kinzel, Nelson, & Heckman, 2009; Kollmann, Vieli, Edwards, Tockner, & Ward, 1999; Tornabene, Bramblett, Zale, & Leathe, 2018; Tracy‐Smith, Galat, & Jacobson, 2012; Vanbergen et al., 2017). However, there is no infor- mation on the colonization of river islands by soil fauna in the Received: 25 September 2018 Revised: 3 April 2019 Accepted: 4 April 2019 DOI: 10.1002/rra.3446 River Res Applic. 2019;1–13. © 2019 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/rra 1