- Beetle diversity and habitat associations of five
prevalent riparian plant communities were examined along
the lower reaches of Big Beaver Creek Research Natural
Area, North Cascades National Park, Washington. These
communities were defined by dominant tree species, and
included Alder Swamps, Cedar-Hemlock Forests, Douglas-fir
Forests, Gravel Bars, and Willow-Sedge Swamps. Monthly
samples were taken with pitfall traps from 10 randomly
selected patches per habitat during the snow-free periods
(mid-June through mid-October) of 1995 and 1996.
A total of 8,179 non-necrophagous beetles was
collected, comprising 4 families and 290 species. Four
families - Staphylinidae (43%), Carabidae (31%),
Elateridae (12%), and Anthicidae (6%) accounted for 92%
of all individuals. Four families encompassed 65% of all
species Staphylinidae (31%), Carabidae (19%),
Elateridae (8%), arid Leiodidae (7%)
A few species accounted for the majority of
individuals. Almost 51% of individuals were found among
just 20 species. The five most abundant species in each
habitat accounted for 33% (Alder Swamps) to 71% (Gravel
Bars) of individuals.
Beetle abundance and species composition differed
among habitats. Abundance ranged from 1,530 (Cedar-Hemlock Forests) to 2,071 (Alder Swamps) . Abundance per
trap per month varied from 16 (Willow-sedge Swamps) to 27
(Alder Swamps). Species richness was lowest in Douglas-fir
Forests (76) and highest in Alder Swamps (119)
Simpson's 1-D index ranged from 0.74 (Douglas-fir
Forests) to 0.96 (Alder Swamps).
Species were categorized as detritivores,
fungivores, herbivores, omnivores, predators, and
unknowns. Individuals and species of predators and
fungivores were generally numerically dominant.
Herbivores and omnivores contributed few species and
individuals. Gravel Bars virtually lacked fungivores and
were the only community with many (more than 30%)
Two patterns of seasonal abundance were evident.
Abundance was highest in June in the two open habitats,
Gravel Bars and Willow-Sedge Swamps, thereafter sharply
and continuously declining into October. Abundance
peaked during September in the forested habitats.
Baseline data was acquired about the North Cascades
National Park beetle faunas, furthering Park goals to
perpetuate habitat and community assemblage integrity.
In a larger context, this information has also enriched
the understanding of the arthropod faunas of the Pacific