Similar patterns of individual niche use are revealed by different time-integrated trophic tracers (stable isotopes and parasites)

Two unconnected time-integrated tracers of niche use provided similar conclusions about individual foraging behaviour and niche adaptations (functional traits in head shape) within a subarctic lake population of Arctic charr (Salvelinus alpinus). Zooplanktivorous individuals mainly from the pelagic zone were characterised by having low δ13C values, high infections of the parasites transmitted by pelagic copepods (especially Diphyllobothrium spp.) and slender heads with long snouts. In contrast, fish individuals that had consumed benthic prey in the littoral zone were enriched in δ13C and had high abundances of parasites transmitted by Gammarus lacustris (Cyathocephalus truncatus and Cystidicola farionis) and a robust head shape. There were strong positive correlations between individual δ13C values and the abundance of the two parasite species transmitted by Gammarus, but a negative correlation between δ13C and the infection of copepod-borne parasites. The close relationships between diet variation (foraging behaviour), the time-integrated ecological tracers (SI and parasites) and functional trophic morphology (niche adaptations) evidently reflect long-term temporally stable niche use of each individual predator. The two independent time-integrated tracers both gave valuable information of specialised trophic behaviour at the individual level, which is an important basis for studies related to ecological (e.g., resource partitioning) and evolutionary (e.g., polymorphism) topics within a population