Fecal detritus

Some authors consider feces of detritivores a part of the detrital pool, but this point of view does not account for the particular role of feces as an intermediate step in decomposition processes. Detritivore feces - animal-processed material of initially vegetal origin, and hence considered animal detritus here - are usually characterized by a narrower C:N ratio than the detritus they are derived from. Besides almost unchanged detrital fragments, detritivore feces contain considerable amounts of amorphous material, being the result of digestive processes. About 30-50% of the ingested detritus is complexed in humic substances in feces of various detritivores. This amorphous feces fraction is subsequently lost rapidly during feces disintegration. Fecal pellets of detritivores are often more readily decomposed through microbial action and coprophagous (Greek: kopros: dung, excrement) animals than the original detritus. Consequently, their C:N ratio rapidly drops during aging. Coprophagy, being promoted by the suitability of feces as environment for microbial decomposers, results in a further mechanical breakdown of already fragmented organic matter, and thus, directly contributes to decomposition processes. Owing to the digestion oflitter-colonizingmicro-organisms during the gut passage, freshly dropped feces usually contain less active microbiota than the leaf litter they are derived from. Further, possibly through both particle fragmentation and differential proliferation potential for bacteria and fungi in gut lumen of detritivores, the bacteria:fungi ratio is in favor of bacteria in the feces of many detritivores. Further changes in the microbial community occur during feces aging and decomposition. Reasons for fast microbial colonization of feces are the high initial content in viable microbial cells and propagules, the favorable surface:volume ratio, and the high content in easily accessible nutrients of a predigested substrate.

Most features of detritivore feces also apply to another particular type of detritus, namely dung (i.e., fecal masses derived from large herbivores (Latin: herba: weed), frugivores (Latin: frux: fruit), carnivores (Latin: caro: meat, flesh), and scavengers on carrion). Among these, fecal masses of herbivorous mammals (e.g., cattle) attract a particularly rich fauna of coprophages - vegetal (algal) material that survives, and is still active after, gut passage is not detritus sensu strictu, as detritus is, per definitionem, dead. Other characteristics, such as distribution in space and time, rather resemble carrion. Alike rotting fruits and dead animals, dung is characterized primarily by its spatial and temporal concentration in discrete and ephemeral patches of high energy and nutrient content. These patches provide home and food to diverse and highly dynamic communities of consumers making short-term use of this transient energy source. Coprophagous representatives are found among dipteran, coleopteran, and microlepidopteran insects, as well as oligochaete annelids. The sequence of coprophagous and coprophilous (Greek: philos: in favor of)

animals that appear on and in dung and the processes they initiate are highly predictable, but in detail depend on the habitat and climate under investigation. Specialized copro-philous fungi, similarly, exhibit a clear sequence of utilization of their habitat, spores of early stages already being present in the dung when it is deposited by the herbivore. Apparently, users of dung are highly specialized, and their community is significantly different from what usually is referred to as decomposers or detritivores. Depending on climate, dung patches may become completely decomposed in less than 2 months but may also last for more than 2 years. Thus, as for most types of detritus, nutrient release is not sudden but extended over a longer time interval, so that detritus provides a long-term store and source of nutrients at the basis of ecosystems.

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