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Soil animal communities contain a large number of species exhibiting a low degree of trophic specialization. Competition between animal species with similar food requirements is frequently reduced by partitioning habitat space and this ecological principle is demonstrated for woodland mite communities. Microhabitat diversity was determined for the litter (L), fermentation (F) and humus (H) sub-horizons using gelatine embedded soil sections and compared with mite species diversity for the same layers of the soil and litter profile. Cryptostigmata species diversity was correlated with microhabitat diversity (r=0.67, P<0.01) in six woodland soils with a range of humus forms. Intra-habitat relationships were determined for one site on two sampling occasions: in November an exceptionally high correlation was obtained (r=0.91, P<0.001) but samples collected in February showed a lower correlation (r=0.63, P<0.01). Within sub-horizon relationships showed significant correlations for the L (r=0.59, P<0.01) and H sub-horizons (r=0.72, P=0.001). The F sub-horizon data were more variable than the other two sub-horizons but a correlation of 0.60 (P=0.05) was obtained for the intrahabitat study.

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It was shown briefly [W. S. Chow, A. B. Hope and J. M. Anderson (1989), Biochirnica et Biophysics Acta, 973, 105-8] that the oxygen evolved per flash from leaf discs, under steady-state flashing conditions and in the presence of background far-red light, gave a valid measure of the number of functional photosystem II (PS II) reaction centres. Further work on this direct and convenient method has been done to optimise conditions for making reliable measurements. It is found that, to obtain the higher estimates of [PS II], corresponding to functionality of practically all PS II reaction centres that bind herbicides, a form of 'light activation' is necessary after a prolonged dark pre-incubation. Without a sufficient number of flashes being given following a long dark incubation, the number of functional PS II reaction centres was underestimated. Provided light activation had occurred, the measured number of functional PS II reaction centres was independent of flash frequencies up to at least 40 Hz. The results strongly suggest that, in steady-state, light-limited photosynthesis, there does not exist any sub- stantial fraction of non-functional or 'slow' PS II reaction centres.