Pedobiologia 47, 257–271, 2003 © Urban & Fischer Verlag http://www.urbanfischer.de/journals/pedo 0031-4056/03/47/03–257 $15.00/0 Population dynamics and life history of the oribatid mite Ameronothrus lineatus (Acari, Oribatida) on the high arctic archipelago of Svalbard Guldborg Søvik 1* , Hans Petter Leinaas 1 , Rolf Anker Ims 2 and Torstein Solhøy 3 1 Biological Institute, Department of Zoology, University of Oslo, P. O. Box 1050, Blindern, N-0316 Oslo, Norway 2 Biological Institute, Department of Ecology, University of Tromsø, N-9037 Tromsø, Norway 3 Zoological Institute, Department of Ecology, University of Bergen, Realfagbygget, Allégt. 41, N-5007 Bergen, Norway Submitted June 28, 2002 · Accepted October 1, 2002 Summary Ameronothrus lineatus was studied in the northernmost part of its distribution range in the high Arctic. Survey sampling was carried out on two sites on West Spitsbergen: a Carex saltmarsh and a smooth layer of cyanobacteria, where the species was the only oribatid mite collected. On the latter substrate all mites were visible and could be sampled by hand, making it ideal for demographic studies. An experimental population was established in microcosms based on the mite- cyanobacteria system, and all three populations were sampled regularly during summer 1998. Our results suggested spa- tial variation in reproductive patterns between local populations. Influence of climatic variation on demography was illus- trated by comparing reproduction in 1997 and 1998. Synchronous larviposition was observed in early summer, but re- cruitment also occurred throughout the season, and gravid females were found on all sampling dates. Both the saltmarsh and the cyanobacteria populations were female biased. A highly synchronous moulting involving at least 80 % of the ju- veniles was observed in July, and it seems that juveniles moult once per season on average.The synchronous moult is sug- gested to be a phenological strategy to exploit the short arctic summer by timing moulting with the warmest part of the season. A generation time of 5 years was estimated. Juvenile stages of one year, continuous recruitment, and high adult longevity (2–3 years) give stable stage structures and stable population dynamics. Key words: Phenology, demography, life cycle, moulting, sex ratio, reproductive biology The diversity of the arthropod fauna in arctic regions is fairly well known (Danks 1981; Coulson & Refseth, in press), and through the International Biological Pro- gramme (IBP) densities, biomass production, nutrient cycling and energy flow of tundra arthropod communi- ties were investigated, with an emphasis on soil sys- tems (Brown et al. 1980; Bliss et al. 1981). Informa- tion on population biology and life history strategies is, however, fragmentary (Danks 1981, 1999). Detailed life histories and demography are known for only a few insect and collembolan species (Addison 1977; Danks 1981, 1999; Hertzberg et al. 1994, 2000; Birke- moe & Leinaas 1999, 2000, 2001). Population studies have been carried out for a few collembolan species (Addison 1977; Hertzberg et al. 1994, 2000; Birkemoe & Sømme 1998). In order to improve our understand- Introduction *E-mail corresponding author: guldborg.sovik@bio.uio.no