Does the introduced brook trout (Salvelinus fontinalis) affect growth of the native brown trout (Salmo trutta)?
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Non-native brook trout have become widely established in North European streams. We combined evidence from an artificial-stream experiment and drainage-scale field surveys to examine whether brook trout suppressed the growth of the native brown trout (age 0 to age 2). Our experimental results demonstrated that brown trout were unaffected by the presence of brook trout but that brook trout showed reduced growth in the presence of brown trout. However, the growth reduction only appeared in the experimental setting, indicating that the reduced spatial constraint of the experimental system may have forced the fish to unnaturally intense interactions. Indeed, in the field, no effect of either species on the growth of the putative competitor was detected. These results caution against uncritical acceptance of findings from small-scale experiments because they rarely scale up to more complex field situations. This and earlier work suggest that the establishment of brook trout in North European streams has taken place mainly because of the availability of unoccupied (or underutilized) niche space, rather than as a result of species trait combinations or interspecific competition per se.
KeywordsAlien species Boreal streams Interspecific competition Multiscale Salmonids
Pekka Hyvärinen, Pekka Korhonen, and the staff of the Kainuu and Taivalkoski Fisheries Research offered logistical help during the experiments. Sini Heino, Jarmo Huhtala, Kaisa Huttunen, Sami Kivelä, Kimmo Kolkkinen, Vesa Rantanen, Tapio Rautiainen, Maare Saraniemi, Olli van der Meer, and Veikko Virkkunen helped us conduct the field surveys. We appreciate the comments made by Jani Heino and three anonymous referees on a previous version of the manuscript. Our research was funded by Maj and Tor Nessling Foundation, Academy of Finland and University of Oulu (Thule Institute).
The experiments comply with the current laws of Finland.
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