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Bioenergetics of the Woodlouse Tracheoniscus Rathkei Brandt in Relation to Litter Decomposition in a Deciduous Forest

White, Joseph James
Ecology 1968 v.49 no.4 pp. 694-704
Acer saccharum, Asimina triloba, Celtis occidentalis, Isopoda, Quercus macrocarpa, Quercus rubra, biomass, copper, coprophagy, deciduous forests, digestive system, ecosystems, energy flow, energy intake, energy metabolism, feces, food intake, habitats, leaves, plant litter, temperature
In feeding tests conducted under laboratory conditions, the woodlouse Tracheoniscus rathkei Brandt showed a preference for the leaves of pawpaw (Asimina triloba), over those of suger maple (Acer saccharum), hackberry (Celtis occidentalis), red oak (Quercus rubra), and bur oak (Quercus macrocarpa). Observations of T. rathkei in experimental gradients show that its behavior is such as to insure continuous activity until a habitat is found that meets its requirements for contact, darkness, low saturation deficit and low temperature (5°—20°C). T. rathkei was able to maintain copper balance without resorting to coprophagy. Differences between copper intake in food and copper loss in feces were accounted for by changes in body copper. The biomass of the population in a representative deciduous forest fluctuates from 0.09 to 0.35 g/m² between January and September and averages 0.208 g/m². This average is equivalent to 635.5 g—cal/m² (1 gram woodlouse = 3.521 g—cal). The energy flow through this woodlouse population is calculated as gross energy intake, 2,799; excretory energy, 1,871; and metabolized energy, 928 g—cal/m²/year. Assuming a caloric equivalent for paw—paw leaves of 4,625 g—cal/g, and an efficiency of assimilation of 33 per cent for the woodlice, the annual consumption of leaves is 0.605 g/m²/year. The low efficiency of assimilation results in the consumption of a relatively large quantity of leaf litter, which passes rapidly through the gut, making available a large fecal substrate favorable for other organisms. Woodlice contribute to the energy flow in the ecosystem, not soi much by being preyed upon by organisms in higher tropic levels as by their contribution to the mechanical breakdown of leaf litter.