Niche characteristics explain the reciprocal invasion success of stream salmonids in different continents

Abstract

An ability to understand and predict invasions is elemental for controlling the detrimental effects of introduced organisms on native biota. In eastern North America, European brown trout generally dominates over, and eventually replaces, the native brook trout. We show here that in northern Europe the pattern of replacement between these two species is reversed: when transferred to North European streams, brook trout spread extensively and partially replaced the native brown trout. The effect of brook trout on brown trout was habitat-specific: brook trout excluded the native species only in small tributary streams where the reproduction of brown trout was severely reduced, whereas in larger streams brown trout was largely unaffected. Thus, the pattern of coexistence among the two salmonids in our study area is approaching that typically observed in North American streams. In both areas, brook trout ultimately settles in small headwater streams, but the process of replacement differs profoundly: in North Europe, brook trout replaces brown trout in headwater streams, whereas in North America these same streams are the ultimate refuge area for brook trout under the invasion pressure by brown trout. Our results underline the importance of knowing species' niche characteristics to explain and predict biological invasions.alien species ͉ biological invasions ͉ trout

Do native brown trout and non-native brook trout interact reproductively?

“…Also, as in North America (Flebbe 1994;Essington et al 1998) and elsewhere in Europe (Korsu et al 2007), brook trout in our study stream used the upstream (i.e., pool-like) sections of the stretch while brown trout was in the downstream (i.e., riffle-like) sections, with an overlap area located in the middle of the studied stretch. In term of spawning micro-habitat, brown trout is known to use spawning sites with high flows, while brook trout preferentially use deep sites with lower flow (Witzel and MacCrimmon 1983;Essington et al 1998).…”

“…Because the genetic stocks of brown trout are considered as tbreatened in many parts of Europe (Almodovar and Nicola 2004), the populations that still remain in headwater streams have high conservation value for the species. However, this is where brown trout is most likely to be affected by the presence of brook trout (Korsu et al 2007). Consequently, more attention should be paid to the effects of brook trout on brown trout reproduction in Europe and to its long-term consequences on natura1 population ecology.…”

“…In South Europe, there is evidence of trophic interactions (Cucherousset et al 2007), but Blanchet et al (2007) suggested that brown trout growth and apparent survival are hardly affected by brook trout, indicating that other mechanisms are responsible. While existence of reproductive interactions and/or hybridization between these species in Europe has been suggested as a potential cause (Korsu et al 2007;Spens et al 2007), it has not been systematically studied.…”

“…However, the reciprocal effect of brook trout introduction on native brown trout in Europe has received less attention and is still controversial. There is evidence of long-term detrimental impact of brook trout on brown trout populations in boreallakes of northem Sweden (Spens et al 2007) and replacement of brown trout by brook trout in headwaters ofFinland (Korsu et al 2007). In South Europe, there is evidence of trophic interactions (Cucherousset et al 2007), but Blanchet et al (2007) suggested that brown trout growth and apparent survival are hardly affected by brook trout, indicating that other mechanisms are responsible.…”

Distribution of non-native brook trout (Salvelinus fontinalis) across Norwegian waterbodies – is it an invasive species?

“…In Finland, brook trout are mostly established in tributary streams, where they may form dense populations that can be harmful to local brown trout populations (Korsu et al 2007, Korsu & Huusko 2009). They found that propagule pressure in terms of the number of individuals released and introduction events leading to highly successful establishment of brook trout, came to about 8000 individuals.…”