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ABSTRACT. In low-order streams, the processing of allochthonous leaf litter is essential in the carbon/energy flow dynamics. Benthic macroinvertebrates, such as chironomids, play critical roles in the breakdown of allochthonous materials, because their larvae take part in intricate trophic networks and have varied trophic ecologies. We evaluated the effects of intra-annual variability on the input of allochthonous leaf litter, and the interactions of leaf-detritus on the succession of Chironomidae assemblages in the dry, rainy, and transition seasons (rainy-dry and dry-rainy). The study took place in a stream in the Brazilian Cerrado. Leaves were incubated in the stream to ascertain the colonization process by Chironomidae and the loss of leaf litter mass after 90 days. Functional feeding groups (FFG) were less rich and less abundant in the dry and dry-rainy seasons, than in the other seasons. The FFG composition of Chironomidae demonstrated that temporal variation between seasons was affected by the exposure time of the leaf-detritus in the stream, and there was more segregation during the dry and rainy seasons. In conclusion, the colonization of leaf-detritus by Chironomidae larvae depended on how long allochthonous plant material remained in the stream, and the variability of the organic matter dynamics input into the stream.
KEYWORDS. Allochthonous materials, benthic macroinvertebrates, functional feeding group, leaf-detritus, richness, temporal variation.
INTRODUCTION
The process of organic matter decomposition is fundamental for the functioning of streams (Graga et al. 2015) and deserves special attention in ecological studies. In conserved riparian vegetation, allochthonous organic matter is one of the primary sources of energy for ecological processes (Warren et al. 2017). Allochthonous organic matter is processed inside the stream, and provide food for benthic macroinvertebrates, and shelter against the flow of water and predators (Moretti et al. 2007, Alonso et al. 2010).
In tropical ecosystems, leaves fall continuously throughout the year, with peaks associated with the rainy season, when more organic matter is available (Tonin et al. 2017). In the dry season, litterfall is often associated with water stress (Gongalves-Jr and Callisto 2013, Gongalves-Jr et al. 2014, Sales et al. 2015). In the Brazilian Cerrado (also known as Brazilian savanna), the greatest litterfall occurs in the transition from the dry to the rainy season (dry-rainy transition season). The fallen debris supply plant biomass to the...