Revue : Ecosphere

Direct and indirect effects of environmental factors on dietary niches in size-structured populations of a wild salmonid

Auteurs :

Musseau C., Vincenzi S., Jesenšek D., Cantera I., Boulêtreau S., Santoul F., Crivelli A.J.

* Auteur correspondant : Camille Musseau (e-mail)

Résumé :

Dietary plasticity of populations can be associated to ontogenetic diet preferences and depends on the size-structure of populations. Dietary niche characterizes the functional role of organisms in a food web, as it reflects both resources’ diversity used by a consumer and trophic interactions in the system. Dietary niches are controlled both by biotic and abiotic factors, but their interactions in natural systems remain poorly studied. Here, we investigated the variability of dietary niche in salmonid wild populations focusing both on inter-population and intra-population (through time) trophic changes, using marble trout (Salmo marmoratus) living in Slovenian headwater streams as a model system. Stable isotope analysis showed high variability of dietary niche and trophic diversity among six of the seven remnant marble trout populations. We observed substantial differences in dietary niche width among populations and within populations through time. Results of partial least square path modelling highlighted opposite effects of immature and mature trout on trophic niche structure. Direct effects of temperature and slope (stream and watershed) were opposite; temperature narrowed dietary niches while slope increased them. Environmental factors (e.g., temperature, stream and watershed slope) had indirect effects on trophic niches after accounting for fish density. Our results showed that size-distribution and sexual maturity are key determinants of the dietary niche width in a population. Increasing density of immature trout tended to widen the dietary niche while increasing density of mature trout tended to narrow it. Environmental factors had direct effects both on resources and consumers densities and indirect effects. Direct and indirect effects were often antagonistic.

Référence bibliographique complète :

Musseau C., Vincenzi S., Jesenšek D., Cantera I., Boulêtreau S., Santoul F., Crivelli A.J. 2015. Direct and indirect effects of environmental factors on dietary niches in size-structured populations of a wild salmonid. Ecosphere 6:art256. doi : 10.1890/ES15-00109.1