French Broad River Macroinvertebrates 



39 



80 

 70 

 60 

 50 

 40 

 30 

 20 

 10 



MM-1 



^CF-1 



III! 



Ill III ( I I I I 



I t I \_L 



J M M J S N 

 1978 



J M M J S N 

 1979 



MONTH/YEAR 



Fig. 6. Total taxa richness per collection, Cherryfield (CF-1) and Morgan Mill 

 (MM-1) creeks, February 1978-December 1979. 



The growth rate of many benthic species varies geographically, 

 principally due to differences in the temperature regime (Vannote and 

 Sweeney 1980). Water temperature will affect either the number of gen- 

 erations per year or the reproductive success of polyvoltine species. 

 Neves (1979) studied the benthic macroinvertebrates of a Massachusetts 

 stream and found that 14% of the standing crop was based on species 

 with two to four generations per year. These polyvoltine species com- 

 prised 32% of the total production. Neves' study was conducted in a 

 stream with a mean annual temperature of 8.3° C. In the French Broad 

 River, higher mean temperatures (about 13° C) might be expected to 

 increase the number of polyvoltine species. We found that taxa with two 

 to three peaks per year comprised 44% of the standing crop at stream 

 stations and 55% of the standing crop at river stations (unpublished 

 data). This implies that polyvoltine species make up a large proportion 

 of the French Broad River fauna. Production studies in the southeast- 

 ern United States must be careful to evaluate this factor. 



For species with similar morphology and feeding type, differences 

 in seasonal distribution may help to avoid competition. Many such spe- 

 cies pairs can be seen in Table 7. A few examples include: Epeorus 



