Decomposer communities are, in their composition and activities, as diverse as or more diverse than any of the communities more commonly studied by ecologists. Generalizing about them is unusually difficult because the range of conditions experienced in their lives is so varied. As in all natural communities, the inhabitants not only have specialized requirements for resources and conditions, but their activities change the resources and conditions available for others. Most of this happens hidden from the view of the observer, in the crevices and recesses of soil and litter and in the depths of water bodies.
Despite these difficulties, some broad generalizations may be made.
1 Decomposers and detritivores tend to have low levels of activity when temperatures are low, aeration is poor, soil water is scarce and conditions are acid.
2 The structure and porosity of the environment (soil or litter) is of crucial importance, not only because it affects the factors listed in point 1 but because many of the organisms responsible for decomposition must swim, creep, grow or force their way through the medium in which their resources are dispersed.
3 The activities of the decomposers and detritivores are intimately interlocked, and may in some cases be synergistic. For this reason, it is very difficult to unravel their relative importance in the decomposition process.
4 Many of the decomposers and detritivores are specialists and the decay of dead organic matter results from the combined activities of organisms with widely different structures, forms and feeding habits.
5 Organic matter may cycle repeatedly through a succession of microhabitats within and outside the guts and feces of different organisms, as they are degraded from highly organized structures to their eventual fate as carbon dioxide and mineral nutrients.
6 The activity of decomposers unlocks the mineral resources such as phosphorus and nitrogen that are fixed in dead organic matter. The speed of decomposition will determine the rate at which such resources are released to growing plants (or become free to diffuse and thus to be lost from the ecosystem). This topic is taken up and discussed in Chapter 18.
7 Many dead resources are patchily distributed in space and time. An element of chance operates in the process of their colonization; the first to arrive have a rich resource to exploit, but the successful species may vary from dung pat to dung pat, and from corpse to corpse. The dynamics of competition between exploiters of such patchy resources require their own particular mathematical models (see Chapter 8). Because detritus is often an 'island' in a sea of quite different habitat, its study is conceptually similar to that discussed in Chapter 21 under the heading of island biogeography (see Section 21.5).
carrion feeders on the sea bed
8 Finally, it may be instructive at this point to switch the emphasis away from the success with which decomposers and detritivores deal with their resources. It is, after all, the failure of organisms to decompose wood rapidly that makes the existence of forests possible! Deposits of peat, coal and oil are further testaments to the failures of decomposition.
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