Longitudinal and altitudinal changes of macroinvertebrate functional feeding groups in neotropical streams: a test of the River Continuum Concept

The River Continuum Concept (RCC) explains the structural and functional characteristics of stream communities focusing on the gradually changing physical components from headwaters to downstream habitats of streams and rivers. The global value of the RCC is still uncertain, possibly because physical factors (e.g., altitude and then temperature, stream order, channel width) can vary differently in longitudinal river axes across the world. Moreover, RCC predictions in relation to different physical factors have not been tested adequately in different biomes, especially biomes outside of temperate North America. Here, we report on the functional structure of macroinvertebrate communities in neotropical streams from Bolivia along a broad altitudinal gradient (from 1120 to 4300 m a.s.l.), aiming to understand how altitude can affect the longitudinal changes in functional feeding groups (FFG) and richness predicted by the RCC. The RCC predictions for functional structure were not completely matched when analyzing FFGs in relation to an index of longitudinal stream gradient. However, after removing the effect of altitude by using residuals from regressions between FFGs and altitude, FFG patterns matched RCC predictions more closely. We detected significant relationships between altitude and the relative abundance of collector-gatherers, shredders and scrapers which may be related to changes in temperature, UV radiation and canopy cover along the altitudinal gradient. Our results indicate that altitude combined with position along the longitudinal gradient is an important factor governing the FFG structure of macro invertebrate communities in neotropical streams.