Biogeographical Trends In Diversity Of Soil Organisms

Interestingly, with the exception of termites, whose diversity declines significantly over a large geographical gradient, numerous taxa of soil organisms, ranging from ciliate protozoa (Foissner 1987a, b) to earth worms (Hendrix, 1995) do not decrease from 0 to 60° latitudinal range. Wardle (2002) suggests two principal reasons: (1) With increasing latitude there is a general trend for greater amounts of organic matter accumulation, and higher amounts of carbon and nutrients are stored in the soil relative to the amount of plant biomass present. Greater humus depth may provide greater habitat heterogeneity and greater amounts of nutrients present in the soil. (2) Diversity of soil organisms may be governed by local factors rather than by regional pool size. If one adds in the fact that numerous smaller soil organisms (soil microfauna and microflora including both fungi and bacteria) can be transported by wind currents and macrobiota over intercontinental distances, one would expect to see pandemic distributions, and this is what is observed (Wardle, 2002).

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