This study is ecological in objective; primarily it attempts to evaluate environmental factors limiting the distribution of a wide-ranging species of fish, Gasterosteus aculeatus, in one sector of its holarctic range. Two approaches to this investigation are made: comparative and deductive. The comparative method is possible because many studies have been made on temperate-zone populations of the species; modified behaviour observed in the present study are consequently viewed as probably adaptive to the different environmental conditions of the north. [...]

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