D. J. Larson. 1998. Beetles in Smith, I.M., and G.G.E. Scudder, eds. Assessment of species diversity in the Montane Cordillera Ecozone. Burlington: Ecological Monitoring and Assessment Network, 1998.

BEETLES (DYTISCIDAE)

D. J. Larson
Department of Biology
Memorial University of Newfoundland
St. John's, Newfoundland
A1B 3X9

INTRODUCTION

The family Dytiscidae, predaceous water beetles, comprises the largest family of aquatic beetles in Canada. The family, containing approximately 270 Canadian species, is represented in virtually all parts of the country, from the high arctic to the most southerly limits and from alpine habitats to oceanic islands.

Dytiscids are principally inhabitants of shallow, littoral habitats, being tied to this zone by their relatively weak swimming abilities, aerial respiration of most, and pupation on shore. Habitats with highest diversity are small, stagnant ponds, and vegetation-rich shorelines of larger ponds and lakes. Characteristic but less diverse faunas also occur in such diverse habitats as saline ponds, springs as well as along the margins of larger rivers and wave-washed lake shorelines. The richest habitat is the emergent vegetation zone including seasonally flooded grasses and herbaceous plants. Over almost all of Canada surface water from spring melting of the winter snow pack and the glaciated landscape with its immature drainage systems containing an abundance of water-holding depressions produce an abundance of habitats for water beetles.

Many Canadian species have wide distributions and in fact about 17% are Holarctic (Larson and Roughley 1991). Many widely distributed species occur in peatlands or Carex marshes, habitat types that are abundant in the boreal zone as well as the low arctic and more southerly forested regions. Another large suite of species occurs in exposed, sun-warmed ponds of prairie or cultural steppe environments as well as in sites where more local disturbances produce forest openings containing shallow waters. A number of species, especially those of open ponds, are good colonizers and appear rapidly after new habitat is formed even when it is apparently isolated. These widely distributed species comprise a significant proportion of the fauna of most regions of the country. However, in spite of the existence of many widely distributed species, species diversity does vary from region to region. Much of this regional diversity is due to species occupying special habitats of regional distribution. For example, halophilic species are restricted to regions with saline waters whereas species of clear, cold, flowing waters are typically found in mountainous areas.

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