Postglacial Dispersal of Freshwater Fishes in the Québec Peninsula

Abstract

The possible postglacial dispersal of freshwater fishes in the Québec peninsula is described. We tested the hypothesis that fish dispersal was controlled more efficiently by movements of the earth crust and by morphological peculiarities of the peninsula than by upland divides presently found between river basins. Based on the actual distributions of 109 species of freshwater fishes, the presence and absence of these species was noted for each of 289 one-degree-square pixels of the peninsula. A geographical intermediate-linkage clustering was run with a spatial constraint, that is, only neighbouring pixels were allowed to cluster. Five main ichthyogeographic regions and 21 subregions were thus defined. The regional limits seem to be highly correlated with climatic, vegetational, and geomorphological limits or gradients. Knowing the fish species present in each subregion made it possible to deduce their pattern of postglacial dispersal, after computing a coefficient of dispersal direction between neighbouring subregions. The pattern of fish dispersal so derived assumes that the stenohaline species have crossed the centre of the peninsula. This can be explained by the isobasic movements since the end of the Wisconsin Ice Age, and also by a network of river headwater interconnections still extant today.