Spatial Structuring of Benthic Invertebrate Communities Within and Among Wooded Headwater Stream Networks

Abstract

Biotic communities in low order streams are influenced by multiple factors that may reflect both environmental conditions within individual watersheds, and also bio-geographic considerations such as spatial proximity of streams and organism dispersal/recruitment abilities. Prior work in small streams of Western New York (Allegheny Plateau) revealed little or no spatial structuring of biota among separate steams, but instead convincing effects of stream and watershed environmental factors. In this study, we further explored the roles of spatial vs. environmental influences by now comparing 1st - 3rd-order streams longitudinally within a stream network in addition to comparing physically separated streams. Within-stream drift adds a new dispersal dimension that is not present between streams. Four stream networks, each with a consecutive series of a 1st, a 2nd, and a 3rd order segment, were selected in a contiguously wooded sector (2nd growth through moderately disturbed old growth northern hardwoods) of Allegheny State Park near the Pennsylvania border. Three replicate Surber samples and a qualitative sample were collected from each stream site in fall 2010 and spring 2011. Similarity/dissimilarity among streams was explored by Euclidean distance matrices for community composition, stream/watershed environmental characteristics (in-stream habitat, watershed land cover, etc.), and spatial distance. Non-metric multidimensional scaling ordination of community composition and Principal Components Analysis ordination of environmental variables of the twelve stream segments were employed. Community composition of in-stream biota was based on the identification of 117 taxa representing fifty-three families. Spearman rank correlation indicated ten out of twelve of most abundant taxa were associated with the larger streams, trending away from the first orders. A One-Factor ANOVA of site-to-site biotic distances revealed no significant differences among longitudinal within stream pairings, like order pairings, and all poss