Distribution patterns of Hydropsychids and Rhyacophilids species (Trichoptera) in a non-regulated Mediterranean river (SW Spain) This paper investigates the longitudinal ordination of the Hydropsychidae and Rhyacophilidae species present in the high basin of the Hozgarganta River. The ordination of the Hydropsychids species present in the basin show three distribution patterns: Diplectrona felix and Hydropsyche infernalis are confined to the head streams; H. siltalai and H. iberomaroccana are

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... stributed throughout the entire study zone, although the second one does not reach the highest sections of the basin; finally, H. lobata occupies the lowest sections, specially in the main axis of the river. The two Rhyacophila species studied show also a well differentiated distribution. R. fonticola is more abundant in the gorges and high sections, whereas R. munda prefers the riverbed of the main river, although it's also found in some tributaries. Even in these intermediate sections, the segregation between the two species is almost perfect. The water permanence in the riverbeds influences the distribution of some species. We have found that D. felix and H. infernalis inhabit the permanent sections of the stream heads whereas H. iberomaroccana significantly dominates the intermittent ones. H. siltalai, H. lobata, R. fonticola, and R. munda do not show a significant preference for any type of riverbed (permanent, intermittent, or ephemeral). It is interesting to highlight the survival of some H. iberomaroccana larvae in isolated pools during the summer. We suggest the possibility that these larvae survive thanks to the existence of a weak underground flow of subsurface origin between adjacent pools.