Food Web and Trophic Basis of Production of the Benthic Macroinvertebrate Community of a Subtropical Stream (Yangtze River Basin, Middle China)

The food web of the benthic macroinvertebrate community of the Tanqigou Stream - a subtropical forested headwater stream of the Yangtze River basin - was investigated for the first time. The results indicated that the stream was mainly a detritus-based system, with its functionality being highly dependent on allochthonous input of organic matter. Vascular plant detritus, filamentous algae, diatoms and fungi were also important food resources for the macroinvertebrate community in the stream. Temporal and spatial patterns of ingestion of four mayflies (which were the dominant species) demonstrated that there was little difference in feeding selection, but significant variations in ingestion patterns were observed, during different seasons and at different sampling sites. Nevertheless, the rates of ingestion of the four mayflies were generally stable and independent of the season or the site. The macroinvertebrate food web encompassed five basic food resources; four top predator species, and 27 intermediate non-predator consumers. The predator-prey ratio was 0.36; the total number of linkages 152; the trophic connectance 0.16; the maximum chain length three; and the mean chain length 2.21. A quantitative assessment of the energy flux along the major food web pathways indicated that organic matter pathways were mainly formed by weak linkages (36), which accounted for 60.31% of the total linkages (63) and that a few pathways accounted for most of the flow of organic matter. This suggests that Tanqigou Stream is similar to streams that are mainly dependant on detritus-based-and allochthonous-input of organic matter.