Microbivory in Caves

As with detritivores in the epigean environment, the primary food of cave cockroaches may be the decay organisms, rather than the organic matter itself (Darlington, 1970). This may be particularly true for cockroaches that spend their juvenile period or their entire lives buried in guano. In Sim. conserfarium, for example, groups of all ages are found at a depth of 5-30 cm in the guano of fruit bats in West African caves (Roth and Naskrecki, 2003). What better microbial incubator than a pile of feces, leaf litter, or organic soil in a dark, humid environment in the tropics? In addition to ingesting microbial cytoplasm and small microbivores together with various decomposing substrates, it is possible that some cave cockroaches directly graze thick beds of bacteria and fungi that live off the very rocks. These include stalactite-like drips of massed bacteria, and thick slimes on walls (Krajick, 2001). In Tamana cave, fungi dominate the guano of insectivorous bats. The low pH combined with bacterio-cides produced by the fungi is responsible for the low number and diversity of bacteria. The pH of frugivorous bat guano, on the other hand, favors bacterial growth, which supports a dense population of nematodes (Hill, 1981). Recent surveys using molecular techniques indicate that even oligotrophic caves support a rich bacterial community able to subsist on trace organics or the fixation of atmospheric gases (Barton et al., 2004).

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