314 CARNEGIE INSTITUTION OF WASHINGTON. 



Destruction of the Range by Prairie-dogs, by W. P. Taylor and J. V. G. Loftjield. 

 Quantitative determinations of the damage done to the range at two of 

 the stations in northern Arizona gave the following results: 



Wheatgrass forage type (4 years' determinations, Coconino, Arizona). 



Proportion of western wheatgrass destroyed by prairie-dogs 69 per cent. 



Proportion of western dropseed destroyed 99 per cent. 



Proportion of total forage (combining the two grasses) destroyed 80 per cent. 



Total forage produced per acre per year 1862 pounds. 



Forage destroyed by prairie-dogs per acre per year 1495 pounds. 



Blue grama forage type (1 year's determination, Williams, Arizona). 



Proportion of blue grama destroyed by prairie-dogs 83 per cent. 



Total forage produced per acre per year 390 pounds. 



Forage destroyed by prairie-dogs per acre per year 324 pounds. 



The Zuni prairie-dog seems to prefer the western dropseed (Sporobolus 

 cryptandrus) to the western wheatgrass {Agropyron smithi). The latter 

 apparently endures grazing by both prairie-dogs and stock better than the 

 former. Where all three are present, blue grama {Bouteloua gracilis) appears 

 to be third in order of preference. Prairie-dogs and cattle feed on the same 

 grasses and prefer them in the same order. Prairie-dogs do not, from all the 

 evidence obtained from 4 years' observation, eat anything that cattle do not; 

 thus they are thrown into direct and often (in times of drought) deadly 

 competition. So far as these experiments go, the prairie-dog can not be said 

 to have a single beneficial food habit. In some overgrazed areas, the total 

 eradication of prairie-dogs as well as reduction in the number of cattle per 

 unit area will be necessary if the forage is to continue to exist. 



Soil Fauna, by G. W. Goldsmith. 

 The Berlese extraction apparatus has been improved by the addition of a 

 thermo-regulator, so that extraction can be carried out under approximately 

 constant temperature. By employing soil which has been thoroughly heated 

 and adding a known number of organisms, the efficiency of the apparatus in 

 removing the soil fauna can be determined. Prehminary results indicate 

 that the efficiency is not the same for the different groups of organisms in 

 the gravel soil used, but is highest for the Acarina. The average efficiency 

 under conditions as usually employed is not far from 50 per cent, but this may 

 be considerably improved by careful temperature-control and by the limita- 

 tion of depth of soil placed on the screens. As a consequence it has proved 

 possible to refine the results of other observers and to check and extend the 

 observations already made on the soil fauna of the Pike's Peak region. 



Principles and Methods of Bio-ecology, by F. E. Clements and W. P. Taylor. 

 The field investigation of the biome, embracing the role of the animals in it, 

 their relation to succession, and the interrelations with plants, has been con- 

 tinued throughout the year, while those aspects of it that are concerned with 

 pollination and migration, soil fauna, and grazing research have received 

 especial attention during the growing season. The quantitative methods 

 applied to the plant community have been found increasingly appUcable to 

 the biome, with such modifications in certain instances as are demanded by the 

 habits of motile organisms. It has become obvious that the developmental 

 system alone gives an accurate and adequate view of the biome with its 

 complex of action and reaction between plants and animals and between these 

 and the habitat. Attention has been focused chiefly on the basic problems 

 of the biome in the grassland formation, not merely because this is the most 



