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Establishment of dreissenid mussels in aquatic systems is often accompanied by major changes in the abundance, diversity, and community composition of benthic invertebrates. However, few studies have been published that address the effects of long-term dreissenid presence on the littoral benthos inhabiting hard substrata in lakes. We present the results of a depth-stratified, quantitative survey of littoral benthos conducted at 4 sites in 1993, just before dreissenid invasion, and in 2008, 14 y after the establishment of dreissenids in Lake Simcoe, Ontario. Average densities of nondreissenid invertebrates were 45× greater in 2008 than in 1993. Amphipods, isopods, chironomids and oligochaetes underwent the largest increases in absolute abundance. The taxonomic diversity of the benthic invertebrate community (α diversity) increased significantly. Community structure was more similar within and between depths and sites in 2008 than in 1993, a result implying lower β diversity of the postdreissenid li...

We examined latitudinal patterns of generic richness in stream insects across the Mackenzie River system in northern Canada. We focused on low- to mid-order tributaries flowing into the river and spanning ∼11° of latitude. Physical-habitat characteristics and water chemistry were examined as factors affecting diversity both at the local and regional scale. No overall latitudinal trend was found in richness, but trends were apparent at the order level. Local generic richness of Ephemeroptera and Plecoptera declined toward the north, Trichoptera generic richness was lowest in the middle of the latitudinal range, and Diptera generic richness increased with latitude. Most orders of aquatic insects followed the expected decline in richness with increasing latitude, but the family Chironomidae was an exception, probably because of their ability to tolerate subarctic environmental conditions and because of the relative absence of potential predation and competition from other invertebrates. Streams were ...

Field experiments were used to assess the importance of intraspecific and interspecific competition in two grazing caddisflies, Neophylax fuscus Banks (Uenoidae) and Pycnopsyche guttifer (Walker) (Limnephilidae) and to examine the effect of larval density on the biomass of their algal food. Chlorophyll a was unaffected by manipulations of the density of either caddisfly species, although indicators of algal "quality" (the ratios of chlorophyll a to ash-free dry weight or to pheophytin a) displayed weak but significantly positive relationships with the dry weight of P. guttifer and N. fuscus, respectively. This suggests that grazing may remove older or overstory algae and thereby prevent senescence of the algal assemblage. Both active larvae and diapausing prepupae of N. fuscus were affected strongly by densities of conspecifics, exhibiting increases in weight only in treatments at 33% of natural density; this suggests a release from intraspecific competition. Survivorship of N. fuscus larvae and prepupae ...