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Drift and Production of Two Aquatic Insects in a Mountain Stream
Author(s) -
Pearson William D.,
Kramer Robert H.
Publication year - 1972
Publication title -
ecological monographs
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.254
H-Index - 156
eISSN - 1557-7015
pISSN - 0012-9615
DOI - 10.2307/1942214
Subject(s) - mayfly , benthos , caddisfly , benthic zone , population density , biomass (ecology) , zoology , invertebrate , ecology , population , larva , biology , environmental science , demography , sociology
The relationships between drift rates, population density, production rates, key environmental factors, and movements of adults were studied in two populations of stream insects, the caddisfly Oligophlebodes sigma and the mayfly Baetis bicaudatus. Samples of benthic invertebrates (424 total) were collected every 28 days at four stations on Temple Fork of the Logan River, Utah, from October 1967 to September 1969. Samples of drift invertebrates (181 total) were collected every 14 days at three stations on Temple Fork during the same period. During June—September a day and a night drift sample (681 total) were collected every other day. Drift rates of O. sigma larvae were greatest (5,987 g/year) when biomass in the benthos (2.56 g/m 2 ) and production (4.30 g/m 2 per year) were greatest. Total production (dry weight) of O. sigma larvae in the stream (bottom area = 29,487 m 2 ) was 89.0 kg in 1968 and 80.8 kg in 1969. Total production of B. bicaudatus nymphs was 41.3 kg in 1968 and 39.8 kg in 1969. Drift rates of O. sigma larvae were related directly to biomass in the benthos over an entire year. Drift rates of O. sigma and B. bicaudatus were not related directly to density expressed as numbers/area in the benthos. Drift rates were correlated positively and significantly (r = 0.78 and 0.55 for day drift of O. sigma and B. bicaudatus, respectively) with density during the months of June—September for both O. sigma larvae and B. bicaudatus nymphs. Discharge, distance below the spring source of Temple Fork, and densities of competing aquatic insects were other factors of significance in the multiple—regression analyses of factors affecting drift rates of the two insects. The 17 or 18 independent variables used in the multiple—regression analyses accounted for 65% and 55% of the variability in day drift rates of O. sigma and B. bicaudatus, respectively. Adult O. sigma (but not B. bicaudatus) undertook a definite upstream migration estimated at 2—3 km. This flight of adults resulted in a concentrated deposition of eggs in the upper reaches of the stream. The advantage of the upstream flight may be that it stores reproductive products in areas where they are relatively safe from effects of anchor ice during winter and of floods in late winter and early spring.