Soil as a Habitat – an Introduction

German

The soil system can be considered to contain various habitat compartments, which are defined by the life history of the animals living therein. Accordingly, different ecological groups of soil animals can be classified.

One compartment is the soil surface including the litter layer, which harbors a multitude of actively mobile invertebrate animal groups that do not or rarely burrow into the mineral soil. Many taxonomic groups live on or in the soil surface and litter layers, such as (in temperate zones) spiders (Araneae), beetles (Coleoptera), false or book scorpions (Pseudoscorpiones), millipedes (Diplopoda), centipedes (Chilopoda), pill bugs (Isopoda), snails (Gastropoda) and many more.

The other habitat compartments are located in the mineral soil itself, where a number of animal groups are (also) found. These may actively burrow through the soil such as earthworms (Lumbricidae) and potworms (Enchytraeidae). The majority of soil-dwelling animal groups cannot burrow and inhabit the available pore space. Animals such as springtails (Collembola), mites (Acari), proturans (Protura) and many larvae (e.g. from Diptera) live in the air-filled pore space. The water-filled or -lined pore space is inhabited by groups such as flatworms (Platyhelminthes), roundworms (Nematoda), rotifers (Rotatoria) or single-celled animals (Protozoa). Many of these groups can also occur in the litter layer. Accordingly, soil can be divided into the following habitat compartments:

Based on their vertical distribution, soil animals can be classified into different ecological groups:

Many taxonomic major groups, such as Collembola or Acari, contain species belonging to the different ecological groups.

Earthworms are classified somewhat differently, depending both on their vertical distribution as well as the burrowing activities:

Another common method of classifying the various and heterogeneous taxonomic groups of soil animals is according to their size (particularly body width):

Some soil animals live permanently on or in the soil, while others only inhabit soils during certain life stages. Soil animals are thus sometimes classified according to their “times of residence” in the soil:

Important are also the trophic resources available in the soil habitat. The disparate soil taxa can therefore also be grouped according to their feeding types:

Being intimately in contact with the soil habitat, the occurrence and distribution of soil animals in time and space is heavily dependent on the habitat conditions and factors. Primary among these are the land-use and biotope type. Although rarely dependent upon individual plant species, the vegetation at a societal level is also a determinant factor. Particularly in wooded areas, the humus form (mull, moder, raw humus) plays a decisive role. Especially for hemiedaphic and endogeic species, the various soil parameters themselves influence the occurrence of soil animal communities, for instance: