Invertebrate drift and colonization processes in a tropical Andean stream

Drift is one of the main sources of recolonizing fauna after disturbance. In tropical Andean rivers where flow might be unpredictable, changes in flow and water velocity can have strong effects on drift and recolonization. To address this issue, we studied drift at the Pibujra high altitude Andean stream (Ecuador, 3300 m asl), by taking diel drift samples at base flow conditions and at dry and wet seasons. Also, we made short (up to 7 days) and midterm (7 to 25 days) recolonization experiments using cobbles located at fast and slow velocity areas in the studied reach. At the same time Surber samples were taken in the stream to relate to drift densities. Baetodes and Leptophyphes were the only invertebrates that showed diel drift periodicity which could potentially be related to the presence of introduced rainbow trout. Drift composition was different between seasons, while drift richness and diversity were highly correlated with flow. Drift propensity in general were higher at the wet season. Recolonization was related to both  drift and benthos composition with higher densities at the dry season, however contrarily to benthic fauna, the most diverse and rich communities were found at fast velocity conditions.