Life histories, secondary production and microdistribution of hydropsychid caddisflies (Trichophtera) in a tropical forest stream

The ecology of seven species of hydropsychid caddisflies was investigated in Tai Po Kau Forest Stream (TPKFS), New Territories, Hong Kong, over a two-year period (1977-79). Quantitative benthic samples were taken from different microhabitats in the stream on 47 occasions and, in combination with light-trap catches of adult caddisflies, were used to investigate life-history patterns and estimate secondary production. Cheumatopsyche spinosa (141.9 individuals 0.5 m-2; 63% of total hydropsychid densities) and C. ventricosa (54.7 individuals 0.5 m-2; 24%) were the most abundant hydropsychids in TPKFS, followed by Macrostemum fastosum (15.2 individuals 0.5 m-2; 7%). Hydatopsyche melli, Herbertorossia quadrata, Polymorphanisus astictus and Hydropsyche chekiangana were present at relatively low densities (each C. spinosa > C. ventricosa > Hydatopsyche melli > Herbertorossia quadrata > P. astictus > Hydropsyche chekiangana. Production:biomass (P:B) ratios varied from 3.59 (Hydatopsyche melli, 1977-78) to 25.46 (Herbertorossia quadrata, 1977-78), and P:B ratios (1977-79) decreased in the order C. ventricosa > C. spinosa > Herbertorossia quadrata > M. fastosum > Hydropsyche chekiangana > P. astictus > Hydatopsyche melli (Table II). Bivoltine species had the highest P:B ratios. All TPKFS hydropsychids (except P. astictus) were significantly more abundant in midstream microhabitats than close to the stream banks. This pattern was most marked in Hydatopsyche melli and Hydropsyche chekiangana. Multivariate statistics revealed that hydropsychid microdistribution was influenced significantly by sediment grain-size characteristics, although algae or detritus also had an influence on all species except Herbertorossia quadrata. Despite the statistical significance of best-fit regression models, the proportion of variation in the abundance of each species explained by the independent variables did not exceed 23% (in C. spinosa), and was typically much less.link_to_subscribed_fulltex