-I — r 



T — I — r 



"T — r 



-1 — I — I — I — I — r— J — I — r 



-I — r 



Lt 



Dork 



Light 



I I I I I I L 



I I I I I I I I I I I I I L 



1600 1800 2000 2200 Mid 0200 0400 0600 0800 lOOO 1200 1400 1600 1800 



night 



Figure 19. The diurnal oxygen consumption rate for a lemming. 



Arthropod populations 



Steve MacLean 

 Don Smith 

 Jim Bamberger 



University of Illinois 

 University of Montana 

 University of Montana 



The objectives of the study on tundra arthropods were 1) to estimate seasonal changes in num- 

 bers of the more abundant arthropod groups and 2) to investigate in greater detail population 

 phenomena and energy flow in one conspicuous and important group, the crane flies (Diptera: 

 Tipulidae). 



Samples for the determination of arthropod abundance at site 2 were taken from the same study 

 plots and quadrats sampled by other subprojects (Tables XVII and XVni). The sampling unit was 

 a 15.2-cm-diam sod core taken to a depth of approximately 10 cm or to the mineral soil. Previous 

 sampling had revealed that very few arthropods were found at greater depth or in the mineral soil. 

 Two cores were taken from each of two sample quadrats from the five destructively-sampled control 

 plots. Thus, the results may be analyzed by sample, or according to nested quadrat, plot, and study 

 site. In this report only summary figures are given. The intensive site control plots were sampled 

 at 10-day intervals, beginning 16 June. Three of the natural manipulations (clip and clear, clip 

 and uncleared, and light -intensity mulch), and the artificial manipulation site control plots were 

 sampled at 10-day intervals, beginning 19 June. The community gradient site was sampled on 22 

 June and at 10-day intervals thereafter. Sod cores were placed in berlese funnels for three days to 

 remove the arthropods. The partially dried samples were then sorted by hand and any additional 

 arthropods were removed. 



The number of arthropods removed per square meter from the site 2 control plots is given in 

 Table XVII. The biomass estimates given for the two crane fly larvae are based on recorded size 

 distributions of extracted larvae and known length: weight regressions. 



The most abundant arthropods were the CoUembola. The recorded densities of 40,000-65,000/ra'^ 

 are at the upper end of the range of densities reported for a wide variety of the world's habitats, and 



44 



