Niche-based and spatial patterns of invertebrate community composition within and among wooded headwater streams in western New York State

Background/Question/Methods

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 streams, 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 by comparing 1^st – 3^rd-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 1^st, a 2^nd, and a 3^rdorder segment, were selected in a contiguously wooded sector (2^nd growth through moderately disturbed old growth northern hardwoods) of Allegheny State Park near the PA border. 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 of the twelve stream segments is also being conducted.

Results/Conclusions

Thus far, evidence suggests stream order plays an important role in community composition, with biotic similarity among 3^rd-order zones (they share a number of “clean-water” mayfly and stonefly taxa), even though they are physically separated. This is similar to the findings of some of our previous work on physically separated streams only. The labor-intensive Chironomidae (midges) are still being processed, but they might possibly yield a similar pattern among the 1^st-order streams where they have tended to be concentrated. There has not yet been any clear indication of biotic similarity longitudinally independent of that based on order alone. However, additional data (perhaps additional taxa), could change this trend. Ultimately the completion of these analyses should enhance our understanding of the complex and dynamic ecology of small woodland streams, especially in terms of the relative importance of niche-based (environmental/habitat) vs. spatial structuring.