Live trapping operations yield demc^raphic data on a large scale; this very quickly over- 

 whelms simple computational methods. A series of computer programs are being utilized to analyze 

 demographic information gathered during the course of this study. The following prc^rams will be 

 utilized. 



1) Instantaneous growth rates 



2) Survivorship curves 



3) Minimum survival rates 



4) Minimum numbers present 



5) Jolly stochastic estimation of numbers present 



6) Juvenile survival 



7) Reproductive status of all animals 



8) Leslie's Z (t) to determine whether sampling is random 



9) Movement patterns 



Energetics of the herbivore populations are being estimated by three measurements: 1) at 

 regular intervals throi^hout the year, 24-hour oxygen consumption measurements are being made 

 with a closed circuit manometric respirometer; 2) snap-trapped animals are autopsied and analyzed 

 for reproductive status, organ weights, total body fat and total animal caloric content; 3) stomach 

 analysis will be made to describe seasonal food habits as well as the amount of ingested vege- 

 tation present. 



Preliminary demographic data (minimum numbers of animals alive on the plot) is shown in 

 Figure 44 for grids A, B, C, D and E. These graphs reveal several interesting phenomena. First, 

 Zapus hunsonicus played a major role as a herbivore for a short period in the middle of the summer. 

 Fairbanks is considered to be a northern limit for Zapus hudsonicus. Past estimates of taiga 

 small mammal populations did not consider Zapus as a component of the subarctic ecosystem. 

 Second Clethrionomys rutilus populations were relatively the same during both summers while 

 Microtus oeconomus and Uicrotus pennsylvanicus densities showed marked fluctuations. Third, 

 Clethrionomys popuUitions in the dense birch and spruce woods were less than half the size of 

 those in open birch woods with a grass understory. 



Clethrionomys rutilus can be the dominant herbivore in a primarily grassland community and 

 at the same time, in a nearby area, be the prevalent small mammal in birch and spruce taiga stands. 

 Zapus hudsonicus has shown high survival rates between the two summers, 1969 and 1970. Nearly 

 50% of the animals tagged in 1969 were recaptured in 1970 as compiired to no recaptures of other 

 species over the same time span in the same area. Preliminary analysis of demographic data show 

 high turnover rates in the Microtus and Clethrionomys populations. At certain limes of the year, 

 as many as 70 to 80% of the animals present one week will be absent two weeks later. 



Ill 



