SOME POPULATION CHARACTERISTICS OF ORIBATID MITES IN STEPPE HABITATS

摘要

Some characteristics of the reproduction mode (sex ratio, rate of gravid females, and mean number of eggs per female) were studied in 19 abundant species of oribatid mites in two steppe habitats of the Trans-Volga region, European Russia. Sex ratio close to 1:1 was found in 9 species, which show no significant changes in the reproduction intensity from May to August. Two more species, lector/bates ornatus (Schuster, 1958) and Microzetorchestes emeryi (Goggi, 1898), reveal larger portion of females inthe populations, yet showing seasonal changes in the population structure. M. emeryi is suspectedly a monovoltinous species with partially overlapping generations. In other 8 studied species males were not encountered despite the females were found to be gravid all during the summer. We consider the reproduction mode of these species as parthenogenetic (thelytokous). In our view no less than 27 thelitokous species making up 30% of the total number of oribatid mite species and up to 50% of the total abundance comprise both studied oribatid mite communities. Only parthenogenetic species form a soil strato-ecological group and a guild of true saprovores in steppe habitats.