378 G. O. Batzli et al. 



o 



c 



200r 



a Trappable Lemmings 



High Year 



o 



E 



~o 



x: 



50 



lOOOh c. Stood ing Crop of Graminoids 



'o 







A 



K 



o 



SI 



FIGURE 10-14. Idealized comparison of lemming density, 

 forage consumption, standing crop of forage and deposition 

 of waste products during years with high and low popu- 

 lations. The calculations for lemmings are based on data 

 presented earlier in the chapter. The density estimates in- 

 clude only animals usually caught in traps (> 20 days old), 

 but consumption and waste are calculated for the entire 

 population. 



during a year when the population is high, assuming 90% solubility, is 

 about 90 mg m"^ The phosphorus pool turns over very rapidly, and 

 graminoids must absorb about 3 mg P gdw"' of plant material produced, 

 assuming an average of 0.3% total phosphorus. Since the peak above- 

 ground standing crop averages 80 g m■^ lemming feces would provide 35 

 to 40% of the required phosphorus. Most of the nutrient release from 

 feces probably occurs during snowmelt in spring. That pulse spurs early 

 nutrient uptake by plants and microbes since phosphorus uptake is pro- 

 portional to phosphate concentration (Chapin and Bloom 1976). Hence, 

 the first three premises of the nutrient-recovery hypothesis appear to be 

 substantiated (Figure 10-13). 



