316 M. Butler etal. 



Pond J 



0-2 

 2-4 

 4-6 

 6-10 



E 0-2 

 u 



I 4-6 

 ^ 6-10 



Mean Length , mm 



20 40 60 80 100 4 8 12 16 



_i I I I I I I 1 



_1 I I I I 



0- 2 

 2- 4 

 4-6 



6-10 



_L 



_!_ 



=> I Aug 1972 

 ZD Chironomldae 

 ■ Tonypodinoe 



J L 



0-2 



. 2-4 =] 



Q. 4 - 6P 

 o 



° 6-10 



Pond X 



n 



23-24 Aug 1971 

 All Chironomldae 



FIGURE 7-9. Vertical distribution of Chironomidae 

 larvae in the fine sediments of pond centers. Percent 

 abundance and mean larval length in each depth inter- 

 val below the sediment surface are shown from four 

 dates in two different ponds. 



Tanytarsus every 2 days for a fourth-instar Procladius. Procladius was not 

 strictly predaceous, for detritus and large diatoms were frequently 

 observed in the guts of smaller instars and occasionally in larger ones. It is 

 reasonable to assume that Procladius larvae would find it easy to locate 

 the numerous, shallow-burrowing early instars and, indeed, most 

 mortality occurred in the smallest instars of Chironomus (Figure 7-10). 

 However, we have no direct evidence that Procladius is size-selective. 

 Population density of Procladius and other predaceous chironomids was 

 so high that each predator would have to ingest only one prey larva per 

 week to account for all of the observed mortality. In addition to the 

 mortality we could deduce from population measures (e.g.. Figure 7-10), 



