PATTERNS OF DIVERSITY IN THE CANADIAN INSECT FAUNA

The diversity of the Canadian insect fauna decreases and its compositi on (at all taxonomic levels) changes as climates become progressively more harsh toward the north. This climatic trend dominates patterns of diversity, but many other factors interact to produce the observed pa tterns. In the arctic, species richness is greatest in the west. Farth er south, overall species richness is greatest in the west (especially British Columbia), associated with coastal and cordilleran habitats, and to a somewhat smaller degree in the southeast (especially Ontario) , associated with deciduous forests and particularly with transitional forests which occupy a large area of southeastern Canada. However, ce rtain taxa am better represented in the west or in the east, depending on present-day habitats and on historical factors. These conclusions, based chiefly on a sample of taxa of different types, are possible on ly because basic systematic work has been carried out to distinguish a nd map the species. Preliminary data on numerical patterns, such as th e numbers of species relative to different potential resources such as host plants in different zones, tend to suggest that the occurrence o f species in the north may depend so heavily on climatic factors that potential resources are not fully exploited and the effects of intersp ecific interactions on diversity are reduced.