Ecosystem Engineers

FIGURE 4.4. Organization of the soil food web into three categories—ecosystem engineers, litter transformers, and micro-food webs (after Wardle, 2002, and Lavelle et al., 1995).

have considerable utility. Finally, the vast range of body sizes among the soil fauna suggests that their effects on soil processes take place at a range of spatial scales. Three levels of participation have been suggested (Lavelle et al., 1995; Wardle, 2002). "Ecosystem engineers," such as earthworms, termites, or ants, alter the physical structure of the soil itself, influencing rates of nutrient and energy flow. "Litter transformers," microarthropods, fragment decomposing litter and improve its availability to microbes. "Micro-food webs" include the microbial groups and their direct microfaunal predators (nematodes and protozoans). These three levels operate on different size, spatial, and time scales (Fig. 4.4) (Wardle, 2002).

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