412 S. F. MacLean, Jr. 



matter by green plants. As a result, soil invertebrates live in an environ- 

 ment that is energy-rich, with up to 80% of the soil dry weight consisting 

 of organic matter (> 1675 J cm"') in the top 5 cm, where most of the ani- 

 mals are found. 



As in other functional units of the coastal tundra at Barrow, the di- 

 versity of animals in the detritus-based trophic system is low compared to 

 that found in more temperate and tropical ecosystems; however, the di- 

 versity of soil invertebrates is not as limited as is that of herbivores. Some 

 taxa that are important soil organisms in other ecosystems are missing 

 altogether (earthworms, isopods, millipedes, ants, termites) or are poorly 

 represented (beetles) in the fauna of the coastal tundra at Barrow. Other 

 taxa, for example mites (Acari), springtails (Collembola), flies (Diptera), 

 and enchytraeid worms (Enchytraeidae), show only a modest reduction 

 in diversity compared with temperate ecosystems, and commonly are 

 quite abundant in the coastal tundra ecosystem. 



Invertebrate carnivores are few; the most conspicuous are the preda- 

 tory cranefly larvae, Pedicia hannai, and beetles of the families Cara- 

 bidae and Staphylinidae. Only two families of spiders, Linyphiidae and 

 Lycosidae, are found, the latter with only a single species. During the 

 summer months soil invertebrate communities support an abundant and 

 diverse group of breeding birds, especially shorebirds or waders. 



ABUNDANCE AND BIOMASS 

 OF SOIL INVERTEBRATES 



The array of microtopographic units that compose the coastal tun- 

 dra was described in Chapter 1 , Sample plots for the study of soil inverte- 

 brates were established in representative units of polygonal and meadow 

 terrain (Table 11-1). The characteristics of the study areas and more de- 

 tailed reports of the data are given by Douce (1976), Douce and Crossley 

 (1977) and MacLean et al.(1977). This discussion draws heavily from 

 these data, and emphasizes higher taxonomic categories. Community or- 

 ganization at the level of species is considered by Douce (1976), Douce 

 and Crossley (1977), and MacLean et al. (1978). Energy budgets are cal- 

 culated based upon abundance and biomass estimated in 1972, for which 

 data were most complete. 



Large differences among microtopographic units are apparent in 

 mean abundance and biomass of the major faunal groups during the pe- 

 riod of biological activity (Table 11-1). A two-way analysis of variance, 

 using density as the dependent variable and plot and sample date as inde- 

 pendent variables, was performed for free-living and plant-parasitic 

 nematodes, Enchytraeidae, Collembola, and three major suborders of 

 soil Acari (Prostigmata, Mesostigmata, and Oribatei). Location made 



