326 



M. Butler etal. 



In summary, Lepidurus arcticus has a high reproductive rate, short 

 generation times, and a resistant resting egg. Thus, its life history 

 characteristics in tundra ponds are not significantly different from those of 

 its temperate relatives (Tnops) which exploit ephemeral ponds. Its 

 strategy is to release as many eggs as it is able, one to three at a time, and 

 to begin releasing eggs as early in the summer as possible in order to 

 minimize the probability of the loss of a generation caused by an early 

 freeze or by pond desiccation. 



Effects of Temperature 



The tadpole shrimp's maximum size is a function of the time of 

 hatching in spring, the length of the growing season, the average 

 temperatures, and the availability of food from year to year or pond to 

 pond (Longhurst 1955). In East Greenland, Poulsen (1940) found the 

 maximum average size of Lepidurus arcticus to be 24 mm. Adults in 

 North Meadow Lake reached 21.9 mm, in Pond A they were 25.6 mm, 

 and in North Meadow Pond 34.4 mm (Figure 7-11). The differences in 

 maximal length between the habitats corresponded to the differences in 

 size when the animals returned to the surface of the sediments in late July 



1600 



o 



I 



0) 

 0) 



k- 

 Oi 



Q 



3 



E 



200 



800 



400 



:^^ 



"T — ' — r 



Pond B 

 (Sediment Surface) 



North Meadow Lake 

 (Water) 



~i — ' 1 — 



10 20 

 Aug 



10 20 

 Sep 



FIGURE 7-13. Cumulative degree-hours greater than 10°C in 

 Pond B and North Meadow Lake (1973). 



