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M. Butler etal. 



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Temperature, "C 



FIGURE 7-15. Respiration per milligram dry weight of 

 three different sizes of Lepidurus at four temperatures. 



However, in 1973 the mean daily water temperatures in the pond did not 

 reach 10°C until 30 June; this was not too different from the temperature 

 pattern in the lake. The difference in the size of organisms in these two 

 habitats was caused not so much by differences in rates of growth but by 

 the time of the melt and the time of hatching of the eggs (Figure 7-11). 



Respiration 



Oxygen uptake was measured in a Gilson respirometer. The small 

 size of the flask restrained the animals so that the measured rates are likely 

 minimal. 



The respiration rates were highest at I5°C and decreased at higher 

 and lower temperatures (Figure 7-14); inhibition at 20°C is unusual for 

 animals but this is a higher temperature than they ever encounter in the 

 ponds. The smaller animals have higher respiration rates per milligram of 

 dry weight (Figure 7-15). In general, the rates per milligram agree with 

 those found for zooplankton (D. Kangas personal communication). 



Production 



The annual net production of Lepidurus, 1 1.5 mg Lepidurus C m~^, 

 was calculated from the increase in biomass, the loss from the population, 

 the mass of exuviae, and the amount of eggs produced (Table 7-5). This 

 estimate covered only 27 June to 27 August, however, and some additional 



