Chapter 6 - Absolute Population Estimates by Sampling a Unit of Soil or Litter Habitat extraction techniques.

The extraction methods described here may be used not only with soils and aquatic sediments but also with plant and animal debris, litter and dung, plant material collected by suction apparatus or other means and the nests of vertebrates. The actual methods for obtaining the samples from these other habitats are discussed in Chapters 4 and 5. In general, the matrix holding the animals will be termed soil if of terrestrial origin and sediment if of aquatic or marine sample origin.

Much of the work in soil zoology was originally aimed at the extraction of a large segment of the fauna by a single method. However, most workers have now concluded that a method that will give an almost absolute estimate of one species or group will give at the most a rather poor relative estimate for another. Not only does the efficiency of extraction vary with the animal, but also with the soil (see table 6.1), the physical properties and size distribution of its particles, its water content and the amount of vegetable matter in it. Therefore, although with certain animals under certain conditions each of these methods will give absolute population estimates, none of them will provide such data under all conditions. Further information on ecological methods in soil zoology is given in Phillipson (1970), Dindal (1990) and Gorny & Grum (1993). Techniques for sorting animals from benthic samples are reviewed by Eleftheriou & Holme (1984); McIntyre & Warwick (1984) and Hartley et al. (1987).

Bees, cicindelid and Bledius larvae, certain crabs and other comparatively large animals that make holes or casts in bare ground or the seabed may be counted directly in situ. In most studies, however, it is necessary both to take a sample and to extract the animals.

Contents
6.1. Sampling
6.2. Bulk staining
6.3. Mechanical methods of extraction
  • 6.3.1. Dry sieving
  • 6.3.2. Soil washing (or wet sieving)
  • 6.3.3. Soil washing and flotation
  • 6.3.4. Flotation
  • 6.3.5. The separation of plant and insects by differential wetting
  • 6.3.6. Centrifugation
  • 6.3.7. Sedimentation
  • 6.3.8. Elutriation
  • 6.3.9. Sectioning
    6.4. Behavioural or dynamic methods
  • 6.4.1. Dry extractors
  • 6.4.2. Wet extractors
    6.5. Summary of the applicability of the methods

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