Life histories, secondary production, and microdistribution of heptageniid mayflies (Ephemeroptera) in a tropical forest stream

The ecology of five species of heptageniid mayflies 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 mayflies, were used as a basis for investigating life- history pattern and estimating secondary production. Electrogena sp. (49.8 individuals 0.5 m-2; 60% of total heptageniid densities) and Cinygmina sp. (15.7 individuals 0.5 m-2) were the most abundant heptageniids in TPKFS, followed by Epeorus sp. (9.1 individuals 0.5 m-2). Iron sp. and Paegniodes capulants, which were present in relatively low densities, made up Electrogena sp. > Epeoruc sp. > Iron sp > P. cupularus in 1977-78, but the sequence was Electrogena > Iron sp. > Epeorus sp. > P. cupulatus > Cinygmina sp. in 1978-79. For the study period as a whole (1977-79), the order was Electrogena sp. > Cinygmina sp. > Epeorus sp. > Iron sp. > P. cupulatus. Production: biomass (P:B) ratios varied from 4.8 (Cinygmina sp., 1977-78) to 11.1 (Iron sp. 1977-78), and P:B ratios (1977-79) decreased in the order Iron sp. > Epeorus sp. > Electrogena sp. > P. culatus > Cinygmina sp. Production calculations and P:B ratios are highly sensitive to the conservative assumptions made about heptageniid voltinism in TPKFS, and therefore may be significant underestimates. Epeorus sp., Iron sp., and P. cupulatus were most abundant in midstream microhabitats but Cinygmina sp. was more numerous close to the stream banks. The microdistribution pattern of Electrogena sp. was less distinct, but larvae seemed to favour midstream microhabitats. Multivariate statistics revealed that the microdistribution of all heptageniids (except Electrogena sp.) was influence significantly by sediment grain-size characteristics rather than by algae or detritus, but the proportion of variation (4-14%) in the abundance of each heptageniid species accounted for by sediment characteristics was low.link_to_subscribed_fulltex