Marine

FIGURE 6.1. Arctic food web (a) as described by Summerhayes and Elton (1923) and as diagrammed (b) by Pimm (1982). (b): (1) plankton, (2) marine animals, (3) seals, (4a) plants, (4b) dead plants, (5) worms, (6) geese, (7) Collembola, (8) Diptera, terrestrial, (9) mites, (10) Hymenoptera, (11) seabirds, (12) snow bunting, (13) purple sandpiper, (14) ptarmigan, (15) spiders, (16) ducks and divers, (17) arctic fox, (18) skua and Glaucous gull, (19) planktonic algae, (20a) benthic algae, (20b) decaying matter, (21) protozoa, (22) invertebrates, (23) Diptera, freshwater, (24) other invertebrates, (25) Lepidurus, and (27) polar bear. [From Pimm (1982) and Pimm and Lawton (1980).]

FIGURE 6.1. Arctic food web (a) as described by Summerhayes and Elton (1923) and as diagrammed (b) by Pimm (1982). (b): (1) plankton, (2) marine animals, (3) seals, (4a) plants, (4b) dead plants, (5) worms, (6) geese, (7) Collembola, (8) Diptera, terrestrial, (9) mites, (10) Hymenoptera, (11) seabirds, (12) snow bunting, (13) purple sandpiper, (14) ptarmigan, (15) spiders, (16) ducks and divers, (17) arctic fox, (18) skua and Glaucous gull, (19) planktonic algae, (20a) benthic algae, (20b) decaying matter, (21) protozoa, (22) invertebrates, (23) Diptera, freshwater, (24) other invertebrates, (25) Lepidurus, and (27) polar bear. [From Pimm (1982) and Pimm and Lawton (1980).]

1983; Parker et al., 1984; Whitford et al., 1983; Hunt et al., 1987; Moore et al., 1988) (Fig. 6.2). These studies and several in the Netherlands (Brussaard et al., 1990; De Ruiter et al., 1993; Moore and De Ruiter, 2000), Sweden (Persson, 1980; Baath et al., 1981, Andren et al., 1990), and the United Kingdom (Anderson et al., 1985) found that microbial-faunal interactions have significant impacts on nutrient cycles of the major nutrients, namely nitrogen, phosphorus, and sulfur (Gupta and Germida, 1989). Some of these studies used assemblages of a few species in microcosms but were beginning to delineate the mechanisms that are important in soil systems in general. Among the fauna, the protozoa were often overlooked, despite the findings by Cutler et al. (1923) that there are important predator-prey interactions between protozoa and bacteria in soils. Clarholm (1985) noted that soil protozoa are avid microbivores and turn over an average of 10-12 times in a growing season, in contrast to many other members of the soil biota, which may turn over only once or twice in an approximately 120- to 140-day growing, or activity, season. These findings were further extended (Kuikman et al., 1990) with the observation that nitrogen uptake by plants may increase from 9 to 17% when large inocula of protozoa are present. The demographics and microbial-faunal interactions provide much of the driving force in the models of nitrogen turnover in semiarid grasslands (Hunt et al., 1987) and arable lands (Moore and de Ruiter, 1991, 2000).

Recent studies have noted the more complex nature of food webs when detrital components are included (Polis, 1991; Hall and Raffaelli, 1993; Scheu and Setala, 2002). DeAngelis (1992), in his treatise on nutrient cycling, devoted an entire chapter to nutrient interactions of detritus and decomposers. His ideas have provided insights into decomposition-nutrient cycling processes. This chapter addresses several aspects of soil biota and nutrient cycling in soils, namely demography and "hot spots" of activity, which are often overlooked in energetics studies of soil systems. These factors are crucial to understanding how organisms and soils interact, and contribute to ecosystem function.

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