Terrestrial Riparian Arthropod Investigations In The Big Beaver Creek Research Natural Area, North Cascades National Park Service Complex, 1995-1996: Part V, Analysis of Arthropod Community Characteristics and Habitat Associations

Glesne, Reed; Brenner, Greg; Labonte, James

Ground-dwelling arthropod communities of nine riparian habitat types were sampled within the Big Beaver Creek Research Natural Area, North Cascades National Park Service Complex, during the snow-free seasons of 1995 and 1996. This study is part of a comprehensive program to develop protocols for the assessment of biological diversity and integrity in the Park Complex. Specific objectives were to characterize arthropod community assemblages, identify environmental factors that influence community assemblage structure, and to provide basic information useful in the design and implementation of future monitoring programs. Results in this report are derived from pitfall traps, randomly placed among 9 selected habitats sampled during four monthly periods (June- October) during 1995. Five of these habitats were re-sampled during the same periods in 1996. Nearly 16,000 adult arthropods representing 448 species of beetles, spiders, ants, and true bugs were captured from 529 pitfall trap samples over the two years of the study. Species accumulation curves, combining two years of sample effort, did not reach asymptotes for most habitats. Accumulation curves using several species richness estimators also indicated that the true species richness remains unknown. Comparisons of species richness estimators at a standard level of effort revealed that the greatest richness was found in willow/carex swamp habitat. Alder swamp habitat consistently exhibited the highest diversity in a comparison of values from three diversity indices. Two-Way Indicator Species Analysis (TWINSPAN) classification of sites by species reduced the original 9 habitats, sampled in 1995, into 6 groups. Separation of habitats into the various groups was based largely upon the distributions of 10 species. TWINSPAN analysis was also completed for the 5 re-sampled habitats, using combined data from 1995 and 1996, resulted in similar groupings of habitats and similar indicator species. Non-metric Multidimensional Scaling (NMDS) ordinations of arthropod data also produced distinct habitat groupings consistent with TWINSPAN results. NMDS analysis revealed a strong gradient in percent canopy cover along Axis 1, and weaker gradients with soil moisture, coarse woody debris, and percent herbaceous plant cover along Axes 1 and 2. Gravel bars were a very distinct group separated from all the other groups along Axis 2. TWINSPAN analysis also showed strong separation of gravel bars from other habitats. Using the Indicator Value index (IV) (Dufrene and Legendre 1997), 36 potential indicator species were recognized for the 6 TWINSPAN habitat groups. TWINSPAN only identified 10 indicator species, and some site groups were only defined by the absence of a particular indicator. Recommendations for design and implementation of future structured inventory and monitoring programs using arthropods are discussed.

Terrestrial Riparian Arthropod Investigations In The Big Beaver Creek Research Natural Area, North Cascades National Park Service Complex, 1995-1996: Part V, Analysis of Arthropod Community Characteristics and Habitat Associations

Collections