The Shannon-Weaver index was near or below 3.0 for most stations. 

 Generally an index above 3.0 illustrates a healthy, unstressed community, 

 while an index below 1.0 is indicative of a monospecific community under 

 stress. The index range of 1.0-3.0 seems to illustrate a community under 

 some stress (Wilhm 1970bc). Stresses upon certain Yellowstone communities 

 might be due to large amounts of inorganic sediments and nondiverse, uniform 

 riverbottom substrate types in some areas. 



FEEDING MECHANISMS 



It is interesting to note that Egglishaw (1964), Macan (1974), and 

 Cummins (1975a) all believe that the microdistribution of a species is deter- 

 mined more by food preferences than by any other factor. Current distributes 

 allochthonous detritus and periphyton which in turn determine invertebrate 

 distribution (figure 43). 



In attempting to determine if faunal zonation occurs in the Yellowstone 

 River, aquatic genera found in the Yellowstone River were grouped according 

 to feeding mechanisms (table 13). A grouping of organisms into zones is 

 difficult. It is necessary to go to a lower taxonomic level than family in 

 describing distribution; e.g., the family Chironomidae is listed under all 

 four feeding mechanism categories and is found at all 20 stations. Four 

 genera in the shredder category confined to the upper river represent, at 

 least in part, the erosional habitat of Cummins (1975a). Genera found in the 

 collector and scraper categories are variously distributed along the entire 

 river, thus obscuring the importance of the intermediate and depositional 

 zones for faunal zonation. It may be necessary to graph the abundance of each 

 genus or each species in order to separate the fauna into habitat zones. More 

 information on feeding habits of individual species is necessary before this 

 can be done. 



CURRENT AND DEPTH REQUIREMENTS FOR INVERTEBRATES 



DATA COLLECTED 



Data from the current-depth studies at Gl endive and Intake are summarized 

 in table 14. In general, current and depth means are similar for both stations 

 and all sampling times. Taxa and number of individuals varied greatly, however. 

 At Glendive the mean number of taxa increased from 3.9 in August to 9.0 in 

 November; a similar trend was evident in the Intake samples. The mean number 

 of individuals increased from 9.1 to 149 at Glendive and from 37.9 to 65.8 

 at Intake. More taxa and more individuals were captured in the October and 

 November samples at both stations than during August and September. December 

 samples would have been valuable, but were unavailable because the lower river 

 froze on November 30, 1975. 



Population estimates from 24 samples at each station are shown in 

 tables 15-18. In August (table 15) the fauna was dominated by Traverella and 

 Hydropsyahe. There was a large difference in the total number of individuals 

 collected at Glendive (1222) and Intake (5199). 



67 



