Population dynamics, life histories and species richness in an epiphytic chironomid community

SUMMARY. 1. The chironomid fauna on the spiked water-milfoil Myriophyllum spicatum was studied quantitatively for a year in a small lowland stream in eastern England.
2. A total of nineteen species, comprising fourteen Orthocladiinae, four Chironominae and one Tanypodinae, was recorded. Population dynamics and life histories of the eight most abundant species were described: Orthocladius (O.) Pe 9, O. (O.) sp. A, Cricotopus (C.) annulator, Rheocricotopus chalybeatus, Tvetenia calvescens, Eukiefferiella ilkleyensis, Thienemanniella majuscula and Rheotanytarsus curtistylus. The number of generations per year ranged from one (O. (O.) Pe 9, O. (O.) sp. A, C, (C.) annulator) to five ( T. calvescens, T. majuscula). Temporal variation in population density often reflected characteristic patterns of the life cycle of each species.
3. Species richness (number of species) for each month ranged between six and fifteen. These observed species richnesses were compared with a null species occurrence model and it was revealed that a significantly higher number of species than expected coexisted in April and May. This may be related to the abundance of diatoms in spring.