Role of fungal patchiness on vegetal detritus in the trophic interactions between two brackish detritivores,Idotea balticaandGammarus insensibilis

摘要

We investigated patterns of resource partitioning between two brackish crustaceans (I. balticaandG. insensibilis) on trophic mosaics of fungal species colonizing vegetal detritus. Laboratory feeding experiments were carried out to assess consumption rates and diet selection of single individuals belonging to five populations. Adults of two co-occurring population of bothG. insensibilisandI. balticaand one population ofG. insensibilis, occurring alone in another habitat patch, were studied. Each individual were offered both fragments ofCymodocea nodosaconditioned by 8 fungal species and sterilized fragments as sole food source for 7 days. Both species preferred "conditioned" detritus but potential resource use was greater inG. insensibilisthan inI. baltica. Individual niche breadth increased and phenotypic variability reduced in the allotopic sample. Trophic similarities were lower between individuals of co-occuring populations than betweenI. balticaand the allotopicG. insensibilis. The results suggest that co-occurrence is an important factor contributing to the enhancement of phenotypic variability and, consequently, to a trophic generalization at population level inG. insensibilis. It emphasizes the role of fungal patchiness on detritus in regulating resource partitioning between the two species.