Protozoan community structure in a fractal soil environment

Protozoan abundance was quantified, and 365 protozoan species were recorded , in 150 soil samples from an upland grassland in Scotland. Across the enti re size range (2-200 mum) protozoan species richness varied by a factor of two, whereas abundance increased by a factor of 20 with decreasing body siz e. As the soil had fractal structure, the relatively flat species curve can be explained if spatial heterogeneity determines species number - for in a fractal environment, heterogeneity will be the same at ail spatial scales. Community structure appeared to approach a temporary steady-state about si x days after re-hydration of dried soil. A simple model based on combining the fractal character of increasing habitat area at smaller spatial scales, with the weight-specific energy requirements of protozoa, provided theoret ical curves of abundance and biovolume on body size which provide a reasona ble fit to real data. We suggest two possibilities - that the apparent comp etence of the theoretical model is fortuitous and the product of poorly und erstood dynamic elements of the trophic structure in the community; or that key elements of protozoan community structure in a fractal soil environmen t may be largely explained in terms of habitat space and energy requirement s.