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Is the diet of a typical shredder related to the physical habitat of headwater streams in the Brazilian Cerrado?
Citation:
Ferreira, W., R. Ligeiro, D. Macedo, R. Hughes, Phil Kaufmann, L. Oliveira, AND M. Callisto. Is the diet of a typical shredder related to the physical habitat of headwater streams in the Brazilian Cerrado? International Journal of Limnology. Cambridge University Press, Cambridge, Uk, 51:10, (2015).
Impact/Purpose:
The USEPA’s NARS survey designs and field methods are applied in large basin stream surveys throughout the U.S., and also in countries outside of the U.S. These applications not only provide valuable tests of the NARS approaches, but generate new understandings of natural and anthropogenic controls on biota and physical habitat in streams. Results from applications in Brazil, for example, not only aid interpretation of the condition of Brazilian streams, but also refine approaches for interpreting aquatic resource surveys in the U.S. and elsewhere. Metrics describing the assemblages of benthic macroinvertebrates are one of the mainstays of biomonitoring in wadeable streams and rivers. Benthic macroinvertebrate feeding guild classifications are commonly employed in formulating indices of stream condition, although these classifications are often based on data collected from relatively small regions. Ferreira and co-authors examined gut contents of macroinvertebrates collected using USEPA NARS stream survey designs and field methods in two large basins within the Cerrado (subtropical savanna) biome of Brazil. Their results provide insight into the food sources of these aquatic insects, and how their food sources and feeding strategies are influenced by riparian vegetation and instream physical habitat. The proportion of food items in the digestive tracts of the larvae examined were closely related to stream physical habitat characteristics, and the food sources and feeding strategies were often in disagreement with published classifications. The authors conclude that studies of feeding habits in multiple regions are needed for accurate classifications of benthic macroinvertebrate taxa into trophic guilds. Such studies would improve the accuracy of stream condition assessments by reducing the number of feeding guild misclassifications that result when aquatic organisms adapt their feeding strategies according to local stream habitat conditions and regional (biomes, ecoregions) environmental characteristics that ultimately drive food availability.
Description:
Macroinvertebrates are important for processing leaf detritus in temperate streams, but studies about their role in tropical streams are scarce and often present conflicting results. We assessed the diet of Phylloicus (Trichoptera: Calamoceratidae) larvae, that is generally classified as a typical shredder, via digestive tract analyses, in streams of two basins of Southeastern Brazil. We classified gut contents as CPOM (coarse particulate organic matter), FPOM (fine particulate organic matter), algae, animal tissue, vascular plant tissue, or mineral material. We hypothesized that the diets of Phylloicus larvae would be related to the physical habitat of the streams (e.g., riparian vegetation, organic matter availability, and morphological characteristics). We found that CPOM content was higher in Phylloicus larvae of São Francisco sites, and it varied between instars in the two basins. FPOM was higher in larvae of Araguari sites. The higher CPOM proportion was correlated with higher riparian vegetation canopy density and higher FPOM proportion was correlated with higher instream brush presence (%) (cover for macroinvertebrates), indicating the importance of riparian vegetation structure in modulating feeding habitats of macroinvertebrates. Algae, animal tissue, vascular plant tissue, and mineral material were very rare in the digestive tracts, and therefore could not be explained by habitat variables. We conclude that the larvae had more flexibility in what they eat than we might expect based on their classification as shredders and they fed on different foods in the two studied basins. Therefore, trusting published classifications from a specific basin may be inaccurate; instead, regional studies of feeding habits are needed for accurate classifications of invertebrate taxa into trophic guilds.
