Guano

Vertebrate excrement is by far the most important nutritional base for cave Blattaria; cockroaches that feed on guano are apparently found on all main continents (Gnaspini and Trajano, 2000). If the vertebrates use the same roosting areas year round, then guano deposition is predictable in space as well as time and can support very large, persistent groups of cockroaches (guanobies). This occurs primarily in the tropics, because there food is available for bats throughout the year (Poulson and Lavoie, 2000). Cave cockroaches feed on the droppings of birds and of frugivorous, insectivorous, and haemato-phagous bats, but not carnivorous bats (Table 13.1 in Gnaspini and Trajano, 2000). The abundance and quality of guano varies not only in relation to the diet of a vertebrate guano source, but also seasonally, depending on roosting sites and the availability of food items (Darlington, 1995a). Communities that develop on guano can be very distinct. In one Australian cave, guano may be inhabited by mites, pseudoscorpions, beetles, and maggots, while in a nearby cave the guano is dominated by cockroaches (Paratemnopteryx sp.) and isopods (Howarth, 1988). Eublaberus distanti living in Tamana Cave, Trinidad, wait nightly buried under the surface of guano, with their antennae extended above the surface. When the insectivorous bat Natalus tumidirostris begins to return from foraging at about 3:00 a.m., the cockroaches emerge to feed on the fresh droppings raining from above. The frugivorous bat Phyllostomus hastatus hastatus is found in the same cave, and though Eub. distanti may burrow through their droppings, the cockroaches do not feed on them (Hill, 1981). None of the six cockroach species found in the caves of the Nullarbor Plain in south Australia are associated with bat guano, but Paratemnopteryx rufa and Trogloblattella nullarborensis utilize bird droppings (Richards, 1971).

Most cockroaches that live on the surface of guano appear highly polyphagous (Richards, 1971) and will take advantage of any animal or vegetable matter present in the habitat. Indeed, species able to benefit from all types of food present in caves have more aptitude for colonizing the subterranean environment (Vandel, 1965). The gut contents of Eub. posticus are indistinguishable from guano, but Darlington (1970,1995a) considers both Eub. distanti and Eub. posticus primarily as scavengers on the guano surface. These cockroaches are not indiscriminant feeders, however, as they will pick out the energy-rich parts of food presented to them (Darlington, 1970). The cave floor in Guanapo is covered with bat droppings, dead bats, live and dead invertebrates, as well as fruit pulp, seeds, nuts, and other vegetable fragments defecated by the bats (Darlington, 1995-1996). In cave passages remote from guano beds the choices are much more restricted. Leaves, twigs, and soil that wash or fall into caves generally form the food base for troglobites (Poulson and White, 1969). There also may be occasional bonanzas of small mammals that blunder into caves but cannot survive there (Krajick, 2001). The ability of many cockroaches to endure long intervals without food, particu larly if water is available (Table 4.3), may allow for exploitation of the deep cave environment. This starvation resistance is based at least in part on the capacity to binge at a single meal when food is available, together with the bacteroid-assisted ability to mete out stored reserves from the fat body when times are lean.

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