Dietary niche expansion and niche shift in native marble trout (Salmo marmoratus) living in sympatry with introduced rainbow trout (Oncorhynchus mykiss)

Abstract

The non-native rainbow trout (Oncorhynchus mykiss) has been introduced worldwide for angling purposes and has established self-reproducing populations in many parts of the world. Introduced rainbow trout often have negative effects on the native salmonid species, ranging from decrease abundance, growth and survival, to their local extinction. Assessing the effects of introduced rainbow trout on the native species is thus crucial to better set up conservation programmes. In this study, we investigated the effects of non-native rainbow trout on the diet of native marble trout (Salmo marmoratus) living in the Idrijca River (Slovenia). An impassable waterfall separates the stream in two sectors only a few hundred metres apart: a downstream sector (treatment) in which marble trout live in sympatry (MTs) with rainbow trout (RTs) and an upstream sector (control) in which marble trout live in allopatry (MTa). Specifically, we investigated using stable isotopes the effects of rainbow trout on dietary niche, diet composition, body condition, and lipid content of marble trout. We found dietary niche expansion and niche shift in marble trout living in sympatry with rainbow trout.Compared to MTa, MTs had higher piscivory rate and showed higher body condition and prereproduction lipid content. Our results indicate that the presence of rainbow trout did not have negative effects on marble trout diet and condition and that changes in dietary niche of marble trout are likely to be an adaptive response to the presence of rainbow trout, and further research is needed to better understand. K E Y W O R D Sbiological invasions, body condition, lipid content, niche segregation, stable isotope analysis, trophic niche breadth

Within‐individual trophic variability drives short‐term intraspecific trait variation in natural populations

“…shows that larger trout have higher trophic positions compared to smaller ones, which is consistent with previous findings on the trophic ecology of marble trout (Musseau et al, 2015(Musseau et al, , 2018 and fish trophic ecology in general (Smith & Reay, 1991). High trophic positions in marble trout populations are caused by a sizeable proportion of fish prey in predators' diet (Musseau et al, 2018). The marble populations investigated in the present study are living in allopatry, therefore, the higher trophic positions are due to cannibalism, which has been directly observed several times during sampling campaigns (A. J.…”

Effects of species invasion on population dynamics, vital rates and life histories of the native species

“…Although rainbow trout is known to take food from other Salmonids, the niche shift of marble trout when occurring in sympatry with rainbow trout in Lower Idrijca was not caused by a niche replacement of marble trout by rainbow trout. Musseau et al () also found that marble trout in Upper and Lower Idrijca occupy a high trophic position (3.5 in Upper to 3.9 in Lower Idrijca), which confirms observations of piscivory and cannibalism in other marble trout populations. Marble trout in Lower Idrijca showed higher δ 13 C than marble trout in Upper Idrijca, which is likely to be caused by the inclusion of rainbow trout as additional prey in the diet of marble trout (Musseau et al, ).…”

“…Musseau et al () also found that marble trout in Upper and Lower Idrijca occupy a high trophic position (3.5 in Upper to 3.9 in Lower Idrijca), which confirms observations of piscivory and cannibalism in other marble trout populations. Marble trout in Lower Idrijca showed higher δ 13 C than marble trout in Upper Idrijca, which is likely to be caused by the inclusion of rainbow trout as additional prey in the diet of marble trout (Musseau et al, ). Marble and rainbow trout living in sympatry are thus competitors for food and space, and we expect effects of this inter‐specific competition on vital rates, life histories and population dynamics of marble trout living in sympatry with rainbow trout, such as faster growth, earlier reproduction, lower survival and lower population densities in marble trout living in Lower Idrijca (sympatry) than in Upper Idrijca (allopatry).…”

“…On the other hand, evolutionary models of community assembly often assume that coexistence of competing species results from the operation of resource partitioning mechanisms (Macarthur & Levins, ). Musseau et al () found only minor overlap between trophic niches of rainbow and marble trout in Lower Idrijca and between trophic niches of marble trout living in Lower Idrijca and in Upper Idrijca. Although rainbow trout is known to take food from other Salmonids, the niche shift of marble trout when occurring in sympatry with rainbow trout in Lower Idrijca was not caused by a niche replacement of marble trout by rainbow trout.…”

Does rainbow trout justify its high rank among alien invasive species? Insights from a nationwide survey in Greece

“…The most substantial evidence of this kind has been produced for the alpine streams of the Rhine and Lake Constance, where large increases in the range and abundance of rainbow trout in recent decades coincided with the decline or collapse of several native brown trout populations (Bassi et al, ; Burkhardt‐Holm, Peter, & Segner, ). There remains a minority of studies that have indicated weak or negligible impacts of rainbow trout on native fishes (Musseau et al, , ; Vincenzi, Crivelli, Jesenšek, & De Leo, ).…”