Drivers of diet patterns in a globally distributed freshwater fish species

Abstract

We analysed data of a globally distributed model organism (brown trout, Salmo trutta) in an attempt to understand relationships among biogeography, prey communities, and climate on diet composition at regional spatial scales (Scandinavia) and thereafter explored whether diet patterns remained the same at global scales. At regional scales, we uncovered comprehensive patterns in diet composition among neighbouring freshwater ecoregions, with site-specific prey communities as the best predictor of the observed prey utilization patterns. Thus, we posit that environmental gradients altering site-specific prey communities and consequently the trophic niche of the predator through bottom-up mechanisms are key in understanding spatial dietary patterns. Proximity was also important for the revealed biogeographic patterns at global scales. We suggest that geographic location (latitude and elevation) as a proxy of environmental heterogeneity is key at small spatial scales, and climate at global extents, to understand spatial dietary patterns. Our findings support the hypothesis that future shifts in prey communities due to climate change will strengthen biographical patterns in feeding of freshwater fishes, with consequences for invasiveness assessment and nature management and conservation.

Reciprocal Role of Salamanders in Aquatic Energy Flow Pathways

“…As already pointed out, the diet composition of salamanders can be explained by site-specific prey community structures and intrinsic factors related to body size (i.e., processes scaling with mouth size). However, it is still unexplored if the diet composition of salamanders follows broadscale patterns and whether environmental factors related to biogeography can be important for determining global patterns in the feeding of salamander species, as previously demonstrated in other vertebrate taxa [53,54]. This represents a promising avenue for future research that needs to be explored in order to accept or refute the view that the diet composition of salamanders can converge across multiple systems or species.…”

“…The consumption of salamanders by fish is also well known [54,[86][87][88], with much research focusing on the effect of fish introductions on amphibian assemblages e.g., [89][90][91][92]. Overall, amphibian species richness is significantly lower in aquatic systems where fish have been introduced [93], demonstrating the importance of predatory fish species as consumers of salamanders.…”

“…For example, Orizaola and Braña [91] found no effect of salmonid presence on two widespread anuran species (common toad Bufo bufo and common midwife toad Alytes obstetricans), but they did find a negative impact on newt species (palmate newt, Alpine newt Triturus alpestris, and marbled newt Triturus Marmoratus) as well as on an anuran species (European common frog Rana temporaria). It should be kept in mind that salamanders usually represent a small portion of fish stomach contents [54,94,95]. Taking the brown trout (Salmo trutta) as an example, the primary dietary components are commonly Ephemeroptera, Diptera, Trichoptera, Plecoptera, and surface prey (terrestrial arthropods and emerged aquatic insects), with salamander remains recorded only occasionally [54].…”

“…It should be kept in mind that salamanders usually represent a small portion of fish stomach contents [54,94,95]. Taking the brown trout (Salmo trutta) as an example, the primary dietary components are commonly Ephemeroptera, Diptera, Trichoptera, Plecoptera, and surface prey (terrestrial arthropods and emerged aquatic insects), with salamander remains recorded only occasionally [54].…”

“…This is key to improving our ability to predict the effects of animal introductions or changes in species distributions due to climate change on ecological processes that function at the individual, population, and community levels. From another point of view, Sánchez-Hernández et al [54] observed an inverse association between mean annual temperature and the global dietary contribution of salamanders in brown trout. Adrián and Delibes [96] concluded that the frequency of occurrence of amphibians in the feces of Eurasian otters tends to decrease with increasing latitude.…”