EFFECTS OF INTRODUCED EXOTIC TREE SPECIES ON GROWTH, CONSUMPTION AND ASSIMILATION RATES OF THE SOIL DETRITIVORE PORCELLIO-DILATATUS (CRUSTACEA, ISOPODA)

The food value of the exotic tree species Eucalyptus globulus and Acac ia longifolia for Porcellio dilatatus was assessed in comparison with that of autochthonous species (alder, pine and oak). Growth rates (GR) were higher for animals feeding on alder leaves, followed by those fe eding on eucalyptus, pine, oak and acacia. Animals feeding on acacia l eaves maintained a constant low weight, with almost no weight gain, du ring most of the study period. Significant differences were detected a mong all litter types, with the exception of pine and oak leaves. Cons umption rates (Cr), Assimilation rates (Ar) and Assimilation efficienc y (AE) followed a different pattern from growth data, with isopods fee ding on pine and on the two exotics showing the highest values. These were followed by isopods feeding on alder and oak leaves, with very lo w assimilation efficiency being recorded on the latter leaf type. Neve rtheless, Growth efficiency (GE) was high for isopods feeding on oak c ompared with alder and eucalyptus, and very low for those feeding on a cacia and pine. The differences in the parameters measured are discuss ed in relation to leaf characteristics (nitrogen and total phenolic co ntents, fungal biomass and leaf resistance). (C) 1998 Elsevier Science B.V.