Seasonal dynamics of benthic detritus and associated macroinvertebrate communities in a neotropical stream

The dynamics of benthic detritus and the structure, composition and functional feeding groups of as- sociated macroinvertebrate communities were followed at biweekly intervals over one year in a 4th-order Andean stream located in a forested hill in SW Colombia. The density of macroinvertebrates and the number of taxa showed a similar bimodal annual pattern with highest values occurring from January to mid-March and from July to mid- October. The accumulated benthic detritus and the invertebrate abundance and community structure were appar- ently controlled by stream discharge. This was confirmed by a cluster analysis of invertebrate assemblages over the year where three groups of sampling dates emerged. The first group occurred during high discharges, the second one under intermediate hydrological conditions and the third coincided with low rainfall and low discharges. Nu- merically, collectors dominated, whereas shredders represented less than 5.3 % of the invertebrates. Unexpectedly, benthic detritus and collector densities were negatively correlated; however, no relation between benthic detritus and the abundance of shredders was found, which may suggest that benthic detritus consisting mainly of plant remains was not a limiting resource in this neotropical stream. Macroinvertebrates appear to have a minor role in the decomposition of plant matter which is consistent with previous observations from the same and other tropical streams. As a consequence, macroinvertebrate dynamics in this stream were more influenced by hydrological vari- ations than by input of plant detritus