Ontogenetic dietary shifts are common in fish and often impact trophically transmitted parasite communities. How parasite species composition and relative abundances change among size classes, and at what rate these changes occur, is rarely examined. Hosts with a broad trophic niche are potentially exposed to a large variety of parasite species. The degree of ontogenetic changes in parasite species composition versus changes in parasite abundance should suggestively differ between thropically generalist and specialist host species. In the present study, we explore ontogenetic dietary shifts and their impact on species composition and relative abundance of intestinal parasites in two sympatric salmonid fish species, Arctic charr (Salvelinus alpinus) and brown trout (Salmo trutta) caught in the littoral habitat of a subarctic lake. Our results highlight a close interplay between ontogenetic dietary niche shifts and alterations in the acquisition of trophically transmitted parasites, leading to host-specific differences in the component community of parasites. Ontogenetic changes in the intestinal parasite community related to dietary niche shifts were distinct but less pronounced in Arctic charr than in brown trout due to a broader and more consistent dietary niche of the former and an ontogenetic shift toward piscivory in the latter. At the component community level, changes in parasite assemblages of both host species were driven by a faster increase in the heterogeneity of parasite relative abundance than in the compositional heterogeneity, a pattern that partly may be related to a rather species-poor parasite community of this subarctic study system. Separating compositional heterogeneity from heterogeneity in relative parasite abundance is important to understand how size-dependent variability shapes parasite communities of host populations.

个体遗传饮食的变化在鱼类中很常见，并经常影响通过营养传递的寄生虫群落。很少研究寄生虫种类组成和相对丰度在大小等级之间如何变化以及这些变化以什么速率发生。具有广泛营养位的寄主可能接触大量寄生虫。寄生虫种类组成的个体发生变化与寄生虫丰度变化之间的变化程度应该暗示性地在人类通俗宿主物种和专科宿主物种之间有所不同。在本研究中，我们探讨了遗传上的饮食变化及其对两种同质鲑鱼（北极鲑（Salvelinus alpinus）和褐鳟（Salmo trutta）的物种组成和肠道寄生虫的相对丰度的影响））被捕获在一个亚北极湖的沿海栖息地中。我们的研究结果突出了个体自发性饮食生态位转变与营养传递性寄生虫获取过程中的变化之间的密切相互作用，从而导致寄生虫成分群落中宿主特异性的差异。与饮食生态位转变有关的肠道寄生虫群落的个体发育变化是明显的，但在北极鲑鱼中，与褐鳟鱼相比，其显着性较低，这是由于前者的饮食生态位更广泛，更一致，而后者则向肉食动物转变。在组成群落水平上，两种寄主物种的寄生虫组合的变化是由寄生虫相对丰度的异质性比组成异质性更快地驱动的，这种模式可能部分与该亚北极研究系统的物种贫乏的寄生虫群落有关。在相对寄生虫丰度中将成分异质性与异质性分开对于了解大小依赖性变异如何影响寄主种群的寄生虫群落非常重要。