266 F. L. Bunnell et al. 



Meadow (25) Basin (25) 



10 



^ 8 



o 



0) 

 Q. 



CO 6 



- 4 



I 



1^ 



i 



Rim (37) 



u 



0) 

 Q. 



E 

 ^ 2 



n 



I? 





I 



Top(33) 



Trough (30) 



r 



FIGURE 8-3. The distribution of 

 species in microtopographic units, 

 and Knox, unpubl.) 



Qblue green 



^diatoms 



n green coccoids 



Q green filamentous 



pr^green epiphytes 

 tiJ and aquatics 



fn euglenoids 

 I yellow green 



numbers of algal 

 (After Cameron 



and Omphalina luteovitellina only on rims. In contrast Omphalina erice- 

 torum has only been found in the relatively moist meadows and polygon 

 troughs, where it often occurs on mats of Sphagnum mosses. 



Algae, including blue-greens, are much more cosmopolitan than the 

 higher fungi in their distribution over the microtopographic units of the 



n 



tundra at Barrow (Figure 8-3). Diversity indices (/? = I -p.logiPd 



i= 1 



range from 4.30 in basins of low-centered polygons to 4.68 on tops of 

 high-centered polygons (Cameron et al. 1978). Equitability measures 

 (h/maxh, given n species) show a similarly small range, from 0.89 on 

 rims of low-centered polygons to 0.94 in wet meadows, suggesting that 

 species diversity is primarily a function of the number of species en- 

 countered rather than the distribution of relative abundance. Again the 

 rims and tops show the highest number of species, 33 and 37 respectively 

 of the 59 species recorded from culture. Basins and meadows yielded the 

 fewest species, 25, but algae there do not show the same dramatic reduc- 

 tion as was apparent in the higher fungi. Ten algal species, six green algae 

 and four blue-green forms, were found in all microtopographic units. 

 Ten percent or fewer of the species recorded are restricted to any one unit 

 and about 50*^0 of the species recorded for any two units are common to 



