Abstract
The importance of aquatic arthropods in the processing of organic matter in fluvial systems is well known, but this topic has been poorly studied in Neotropical rivers. In this research, we studied the composition of functional feeding groups (FFGs) associated with differences in elevation in a tropical river in northern Colombia during the wet and dry seasons. Between 2008 and 2013, we collected benthic arthropods at 3 sites located in the upper (San Lorenzo), intermediate (La Victoria) and lower (Puerto Mosquito) sections of the Gaira River. We found some differences in the gut contents and FFGs of the animals from different sites and between the climatic seasons. The dominant food source at all the sites and during both seasons was fine particulate organic matter (FPOM). At La Victoria, the generaLeptonema,SmicrideaandPhylloicus(all belonging to Trichoptera) presented significant differences in the consumption of coarse particulate organic matter (CPOM) between the rainy and dry seasons (p < 0.05). At San Lorenzo,Leptonemahad the highest animal tissue consumption value (p < 0.05). A discriminant function analysis based on gut contents suggested that some taxa may have been assigned to the wrong FFGs. We concluded that the diets of the aquatic arthropods in our study tended to present high trophic plasticity. Consequently, our results suggest that Neotropical rivers need to be re-evaluated in terms of traditionally established FFGs, which heretofore have been based on information from other regions of the world, producing incorrect assessments of aquatic systems.
Highlights
The degree of allochthonous contributions to organic material, principally coarse particulate organic matter (CPOM) from the leaf litter of riparian vegetation to mountain rivers, varies along elevation gradients
The greatest abundance of shredder-detritivores (Sh-Dt; organisms that cut or chew pieces of dead plant material) is expected at higher elevations, scrapers (Sc; organisms that scrape biofilm and algae from the surface of rocks and vegetation) are mainly found in intermediate sections and collector-gatherers (CG; organisms with modified mouthparts that collect particles,
We identified and quantified the area occupied by each food item that was found in the gut contents; the area of each item was calculated with respect to the total area occupied by all items
Summary
The degree of allochthonous contributions to organic material, principally coarse particulate organic matter (CPOM) from the leaf litter of riparian vegetation to mountain rivers, varies along elevation gradients. Analyses from different environments in Colombia, namely Gorgona Island (Longo & Blanco 2014a,b), the Risaralda region streams (Chará-Serna et al 2012) and the rivers in the Sierra Nevada de Santa Marta (TamarisTurizo et al 2007, Guzmán-Soto & Tamaris-Turizo 2014, Granados-Martínez et al 2016), have shown that trophic groups or FFGs for the same taxa that have been collected in different geographic regions are not consistent with the available literature (Torres-Zambrano & Torres-Zambrano 2016) In these studies, changes in diets along elevation gradients have not been evaluated and neither has the trophic variation resulting from differences in climatic periods. We compared the spatial (elevation) and temporal (dry and rainy seasons) variations in trophic characteristics of the aquatic arthropods and determined whether the FFGs that were defined for the same taxa in other regions were consistent with those observed in the studied Neotropical river
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