Seasonal Variation in Standing Crop and Species Diversity of Insect Communities in a small Quebec Stream

Seasonal changes in the distribution and abundance of insects species were studied in a small cool woodland stream where the primary food material was fallen leaves. Between March 1966 and March 1967, weekly quantitative samples were taken from sand, gravel, stone, leaf, and leaf detritus habitats. The number of insects per unit area of each habitat was least in sand and increased through gravel, stones, leaves, and detritus. Biomass per unit area was least in gravel and increased through detritus, sand, leaves, and stone. The annual standing crop of the stream as a whole was approximately 3,000 insects/m2 and 2 g/m2 (dry wt.). The number of insect species in any one habitat varied according to apparent spatial heterogeneity of the environment, to substrate stability, and to food resources. Leaves supported the highest number of species (92), sand the least (61). Species diversity was higher during summer and winter than during spring and autumn. When compared with other aquatic environments, the bottom fauna of the stream has oligotrophic features, including a large number of species and an annual standing crop of poor to intermediate richness.