Abstract:
A census of microarthropods at Akatarawa during 1964-5 shows 25 species of Collembola and 39 species or groups of Acari. From regular samples of constant size, frequency, dominance and density values are calculated. The total microarthropod population is estimated at 100,645 per square metre to a depth of 18 cm, made up of 22,395 Collembola and 78,250 Acari, Collembola, Cryptostigmata and Prostigmata numbers fluctuate seasonally reaching peak abundance in June. A maximum density in this month of 329, 819 microarthropods per square metre is higher than any recorded from British pastures, but a little lower than that given by Hairston and Byers of 423,290 in a pasture in Michigan, U.S.A. The microarthropods are concentrated mainly in the 0-3 cm layer, but some evidence of seasonal vertical migration is noted among the Collembola. Populations are mainly aggregated, but this varies according to species and season. Significant correlations are found between population densities and changes in soil temperature and moisture. Laboratory experiments on growth and oviposition rates in Collembola provide further information on seasonal fluctuations in density, and the existence of strong group association within the plot is demonstrated. Feeding studies in the laboratory show that Brachystomella parvula (Collembola) exhibits a specialized form of feeding.
