ECOLOGICAL SEGREGATION OF LARVAL BLACK FLIES (DIPTERA, SIMULIIDAE) IN NORTHERN SASKATCHEWAN, CANADA

Contrasted degree of habitat differentiation of cytospecies groupings with morphotaxon groupings of black flies collected within a small region offering extensive, spatially continuous simuliid larval habitat. Relative abundance of larvae was correlated with 16 physical and chemical attributes of 20 sites on streams near Uranium City, Saskatchewan. The presence of 20 species, distributed among 14 morphotaxa was identified. Principal components analysis of physical and chemical measurements distinguished 5 groups of variables that were related to 1) stream size, 2) pH, conductivity and turbidity, 3) oxygen saturation and substrate particle size, 4) proximity to lake outlets, and 5) current velocity. Cytospecies belonging to species complexes tended to reach maximum relative abundances at different points along environmental gradients related to stream size and proximity to lake outlets. Cluster analysis of similarity in relative abundance of cytospecies among the 20 sites delineated 7 groups. Reanalysis of sites according to morphotaxon data produced 6 groups. There was only partial congruence between groupings of the 2 analyses. Cytotaxonomic group sites were each characterized by a distinctive combination of stream size and proximity to an outlet; sites classified as having similar morphotaxa were not environmentally distinct from river sites characterized by different morphotaxon assemblages. Thus, simuliid cytospecies represent distinct ecological entities, each adapted to particular suites of environmental variables. -Authors