Colonization of Natural Substrates by Stream Benthos

Abstract

Natural substrates in mesh cages in a Tompkins County, New York, woodland stream were colonized by benthic invertebrates for periods of 3, 6, 9, 12, 18, 24, 30, and 42 d during autumn 1980. An experiment was designed for the purpose of distinguishing seasonal phenology from site-specific temporal (nonseasonal) succession of colonizers. Subsequent to initial colonization, patterns of species dominance were analyzed to develop hypotheses on the potential for biological interactions as explanations for observed patterns of species succession. Total benthos and species richness increased significantly with duration of exposure of experimental substrates indicating the occurrence of nonseasonal succession. However, seasonal fluctuations in abiotic variables (water temperature, current, and water depth) were also shown to have significant effects on colonization. Colonization patterns were species specific; although most species showed gradual increases in numbers given longer exposure of substrates, some showed peak densities within the first few or after intermediate sampling periods, suggestive of competitive displacement of early by later colonists. Association analysis was conducted on the abundances of 19 species pairs within four functional feeding groups to determine the degree of co-occurrence in cages or concordance of colonization patterns. Negative associations were notably absent, and positive associations were common, especially among the filter-feeders and shredders. Positive associations could be interpreted as evidence for lack of ecological divergence (no competition), or potential for present competition. This study documents the existence of site-specific temporal succession of invertebrates in a temperate woodland stream, but does not resolve the question of the importance of biological interactions in determining community changes following initial colonization. Data gathered on a smaller spatial scale would be more sensitive to detecting negative species associations.