SOIL ORGANISMS - Soil Ecology - page 345

1. Microfauna, which comprise aquatic invertebrates that live in the water-filled soil
porosity. They are small, less than 0.2 mm on average, and include the protists and
nematodes, together with other groups of lesser importance like tardigrades, rotifers;
2. Mesofauna, which comprise microarthropods (mainly Collembola and Acari) and
the small Oligochaeta and Enchytraeidae; they have an average size range of 0.2-2 mm
and live in the air-filled pore space of the soil and litter,
3. Macrofauna, which include invertebrates with an average length greater than 2 mm.
Termites, earthworms and large arthropods are the main components of this group.
They have the ability to dig or eat their way through the soil and create specific struc-
tures to accommodate their movements and living activities ( e.g, burrows, galleries,
nests and chambers) and produce casts and faecal pellets through their feeding activities.
These organisms have also been called 'ecosystem engineers' ( sensu Jones et al., 1994)
for their ability to profoundly affect the soil structure and hence influence major soil
processes through the structures that they build (Stork and Eggleton, 1992).
Three major guilds of soil invertebrates may be distinguished on the basis of the
relationship that they have with the soil micro-organisms and the kinds of excrement and
other biogenic structures that they produce (Figure III.61).