Species-specific utilization of food sources by sympatric woodlice (Isopoda : Oniscidea)

1. In long-term laboratory studies, the influence of different food materia ls on parameters of population dynamics was compared in the sympatric woodl ice, Porcellio scaber and Oniscus asellus, as a measure of interspecific di fferences in the utilization of food. 2. Freshly fallen leaf litter of different tree species had been acidified and microbially inoculated prior to the experiments. By analysing the influ ence of pH level, density and activity of litter-colonizing microbiota and several physico-chemical characteristics of the leaf litter, we obtained in formation on those factors that determine food quality. 3. The studied species responded similarly to different leaf litter species in that both P. scaber and O. asellus performed better on litter with low C:N ratio. Overall, both isopod species reproduced more successfully on lit ter with higher pH levels, containing half the levels of tannins and other phenolics. 4. Interspecific differences were obvious with respect to the significance of litter-colonizing microbiota, and the dependence of juveniles on particu lar food parameters. While the performance of adult P. scaber was influence d by both litter-colonizing microbiota and physico-chemical characteristics of the leaf litter, adult O. asellus were influenced by leaf litter charac teristics, but not by litter-colonizing microbiota. Juvenile mortality was affected by the tested food parameters in O. asellus, but not in P. scaber. Growth rates of juveniles of both species were influenced by physico-chemi cal characteristics of the leaf litter. Additionally, leaf litter microbiot a had a significant influence on growth rates in juvenile P. scaber, but no t in juvenile O. asellus. 5. Reasons for, and consequences of, similarities and differences between t he observed sympatric species, and intraspecific differences between ontoge netic stages, are important aspects of soil ecology and may help explain th e sympatric coexistence of two species belonging to the same guild of sapro phagous soil animals.