Role of fungi in the trophic niche of the congeneric detritivorous Asellus aquaticus and A. coxalis (Isopoda)

The importance of various fungal samples, isolated from plant detritus, and of the plant detritus itself in the trophic niche of Asellus aquaticus (L.) and A. coxalis Dollf., was studied in the laboratory. We observed that: (1) The fungi and not the plant detritus, from which they are isolated, constitute the energy source for both species. In fact, the animals to whom the sterilized detritus was offered died within a few days. The animals to whom the fungal colonies were given had significantly higher survival and body growth compared to the controls; (2) The various fungal samples, offered as sole source of food, were used with different efficiency, both by animals of the same species and by animals of different species; and (3) The heterogeneous fungal populations, present in nature in the detritus, constitute a food resource mosaic which permits an even distribution of the trophic resources between two ecologically similar, cohabitating detritivorous species.