Abstract
It is well known that stream macroinvertebrates usually show aggregated spatial distributions caused by extrinsic factors and interactions among species and individuals. In the present study, the spatial distribution of caddisfly assemblages and coexistence patterns of larval caddisfly species (Insecta: Trichoptera) were measured in a Hungarian stream reach at three different spatial scales.
Caddisfly assemblages showed aggregated, random and regular distributions as measured by the variance‐mean relationship of species richness as sampling area increased from 0.0225 m^2^ to 0.2025 m^2^. The observed coexistence patterns indicated interactions (lower diversity of unique species combinations than expected by chance) among species for aggregated distributions. These interactions among species proved to be positive associations particularly among species belonging to the same functional feeding group.
The positive associations and the aggregated distribution of caddisflies supported the hypothesis that microhabitat patches (patchy microhabitat‐macroinvertebrate model) and/or positive biological interactions among species using the same resource (hypothesis of facilitation) have a deterministic effect on the spatial distribution of caddisfly assemblages. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)