The Detritus-Based Trophic System 433 



TABLE 11-5 



Estimates of Energetic Function (J m'^ yr'J of 

 Major Invertebrate Groups in the Coastal Tundra 

 Ecosystem 



ized in Heal and MacLean 1975). Thus, estimates of consumption, as- 

 similation, production, and respiration are not independent. 



The results (Table 11-5) emphasize the importance of Enchytraeidae 

 in this coastal tundra ecosystem. The energetic role of enchytraeids far 

 exceeds the sum of all other invertebrates, and is exceeded by lemmings 

 only in the year of a population high (Chapter 10). Even then, the enchy- 

 traeid value is achieved in an active period of about 100 days, while lem- 

 mings are active year-round. Enchytraeidae are similarly important in 

 tundra-like moorland of the British Isles, where they accounted for 46 

 and 55% of the assimilation of energy by animals in two habitats on peat 

 soils (Coulson and Whittaker 1978). On high arctic tundra on Devon 

 Island, N.W.T., Canada, nematodes were the major invertebrate con- 

 sumers on a dry cushion plant-Hchen community, while Enchytraeidae 

 were the dominant consumers in a sedge-moss meadow community 

 (Ryan 1977). 



The estimated annual production of the two abundant cranefly spe- 

 cies, Tipula carinifrons and Pedicia hannai, was compared with the an- 

 nual emergence of aduh flies estimated earlier (Table 11-4), assuming an 

 energy value of 22.6 J mg"' of tissue produced. The emergence values 

 (35.3 and 19.6 mg m"^ yr"' respectively) represent 15.9 and 11.6% of the 

 estimated annual production of larvae. Since larvae lose approximately 



