Patterns of variation in secondary production in a tropical stream

Abstract

Secondary production of insects in a Hong Kong stream was measured over two years when the intensity of monsoonal rains (influencing stream discharge) showed marked inter-year variation. Data for 19 species (Ephemeroptera, Odonata, Trichoptera and Coleoptera) revealed considerable variation in production between years by some species. A hypothesis that these fluctuations reflected microhabitat occupancy was tested and supported by the data. Production by rheophilic species living in coarse substrates increased during the year with higher stream discharge while that of species living in depositional habitats declined. The opposite trend was observed during the year with low rainfall. Despite variation in annual production of individual species, where data were available for an entire functional feeding group (e.g. filter-feeders), production estimates were rather constant between years.