Graduate Thesis Or Dissertation
 

Life history and production studies of Sialis californica Banks and Sialis rotunda Banks (Megaloptera : Sialidae)

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  • Comparative ecological studies of Sialis californica Banks and Sialis rotunda Banks were made in Western Oregon from 1966 to 1968. Field collections for S. rotunda were made in fish holding pond at the Oak Creek laboratories, 5 miles west of Corvallis, Benton County, and for S. californica in enriched sections of Berry Creek experimental stream, 13 miles north of Corvallis. Life histories were determined in aquaria, in laboratory streams and the natural habitats. S. rotunda, predominantly a pond species, completed its life cycle in one year in all situations. S. californica, commonly a stream species, took one or two years depending on oviposition time and food availability. Both species were reared successfully in the laboratory through all stages of their life cycle. There are ten larval instars. The larvae are carnivorous and feed on insects and other small benthic organisms. Biweekly or monthly samples were collected from the two locations for density, biomass, growth rate and production studies. Density and biomass of S. rotunda in the pond were much higher than for S. californica in the stream. Enrichment with sucrose and urea resulted in differences in density and biomass of S. californica between the four experimental sections at Berry Creek. The unenriched section usually had a high density but low or similar biomass compared with the enriched sections which had few individuals. The lower density in the enriched sections was associated with unfavorable substrate conditions for early-instar larvae because of dense mats of the filamentous bacterium, Sphaerotilus natans. Larger larvae were not hindered by the S. natans filaments and had rapid growth because food was abundant. Production of both species was calculated by two methods: (1) Ricker's (1946) method, the product of growth rate and mean biomass; and (2) Allen's (1951) graphical method, using numbers per m² and mean individual weight at each sampling date, The results from both methods were comparable, with the graphical method usually providing a slightly higher estimate of production. Annual production of S. rotunda in the pond was 13.18 Kilocalories/ m². This was more than double the production of S. californica in any of the sections of Berry Creek. In Berry Creek, the population in the unenriched section had low growth rate but the density of larvae resulted in high biomass and a comparable production to that in the enriched sections. The accumulated annual production was: unenriched, 4.94 Kilocalories; enriched, 6, 34 Kilocalories. The relationship between larval growth and food consumption rate was established by experiments in laboratory streams during summer and winter. These data were used to estimate food consumption by field populations. In the pond, S. rotunda larvae consumed 137 gms/m²/year. In Berry Creek, individuals in enriched sections consumed one and half to two times more food than did individuals in the unenriched section.
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