The Detritus-Based Trophic System 437 



TABLE 11-8 Biomass of Invertebrates (mg m'^Jin the Coastal Tundra 

 at Barrow Partitioned According to Trophic Function 



The microbial feeders (bacteria and algae grazers, and fungivores) 

 make up the majority of the biomass of the soil fauna. This contrasts 

 with many forest ecosystems where large populations of saprovores such 

 as earthworms, millipedes and isopods may dominate the litter and soil 

 fauna. Consumption by saprovores amounts to approximately 9 gdw 

 m'\ about 4.5% of the total annual input to the detritus-based trophic 

 system. In contrast, fungal-feeding invertebrates consume over 18 gdw 

 m"% an amount in excess of the mean annual standing crop of fungi. 



Animals are influenced by both availability and quality of their 

 food. The food of microbivores is less abundant but of higher quality 

 (higher in soluble carbohydrates and nutrients and more easily digested) 

 than that of herbivores and saprovores. It may be that animals using a 

 low-quality diet are at an extra disadvantage under the severe conditions 

 of the Arctic. Schramm (1972) investigated the interaction of tempera- 

 ture and food quality as determinants of growth rate of herbivorous in- 

 sects. Diets low in protein produced poor growth at all temperatures. 

 Diets lacking in low molecular weight carbohydrates (starch and sugar) 



