Measurements were made to determine velocity and depth preferences of 

 invertebrates. All velocity measurements were made with a Price model -AA- 

 type current meter at six-tenths total depth. 



Discharge at the Miles City and Sidney stations on dates sampling was 

 preformed is shown in Table 1 (USGS 1976). 



Table 1. Discharges of the Yellowstone River at Miles City and Sidney 

 during sampling periods (cfs). 



Date Miles City Sidney 



August 6, 1975 20,200 21,200 



August 7, 1975 18.500 20,300 



September 9, 1975 9,890 10,100 



September 17, 1975 8,440 8,980 



October 9, 1975 8,000 9,730 



October 15, 1975 8,850 10,300 



November 7, 1975 8,620 10,400 



November 11 , 1975 10,300 10,100 



CONVERSIONS: 1 cfs = .0283 m 3 /sec 



SPECIES DIVERSITY CALCULATIONS 



Aqgreaations or communities of aquatic orqanisms are subjected to almost 

 continual stress due to environmental changes, some natural and others caused 

 by society. It is a generally accepted axiom in ecology that a gross 

 environmental stress exerted upon a diverse biological community (one 

 consisting of a large number of species) results in a simplication of the 

 system through a reduction of species diversity (i.e. number of species) 

 (Cairns 1969). Slobodkin and Sanders (1969) developed the stability-time 

 hypothesis to suggest the kinds of animals that must live in low- and high- 

 diversity places: all places of high diversity would have stable or predictable 

 environments, and all places of low diversity would either be places of 

 unpredictable hazard or would be short-lived. This theory was tested in one 

 widespread, stable environment—the ocean floor. Although this investigation 

 is far from complete, the theory appears to hold. 



In low-diversity areas, the dangers of species extinction are great. 

 Populations of opportunistic animals must frequently be decreased by weather 

 to prevent it, and the possibility still exists of breeding failure. The 

 loss of several consecutive year-classes means extinction even for long-lived 



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