Ecol:U 



Dor^dainus , Mononchus , Approximately 800 ml. O2 per kg. 

 CephalobuS ) Rhabdit is, per hour 



Achromadora , Acrobeles , etc. at 16° C. 



The metabolism is little influenced by their activity. Narcotized and 

 immobile worms respire at a rate only about S per cent lower than active 

 worms. Immature worms respire at a higher rate than sexually nature and 

 larger individuals of the same species. Respiration increases with 

 temperature up to a certain point. 



With these data in hand, we can calculate the order of magnitude of 

 oxygen consuraption per unit area of soil due to nematodes when the popu- 

 lation density is known together with its species composition. 



I have obtained population densities in a number of Danish habitats. 

 They vary from about 100,000 to 20 million per square meter, correspond- 

 ing to about 1-20 grams per square meter according to the nature of the 

 habitat. The oxygen consumption of nematodes is calculated to vary 

 between 0.5 and 17 ml. Og/m^ at 16 C. 



This leads me on to my last point. It might be interesting to try to 

 express the activity of nematodes in a way which will be more informa- 

 tive. On the basis of population estimates, temperature measurements, 

 and water tension data of one particular grass field in 1955, I have 

 arrived at the following annual budget: 



Nematode population = 20,000,000/sq. m. 



Weight = 20 g. 



Op consumption = 625 mVyear 



In this particular habitat, U/7 of the respiration was due to nematodes 

 which largely feed on bacteria, i. e. 36O m-^02/year. I shall only con- 

 sider this part of the population. If we assume that bacterial dry 

 matter consists of 50^ protein, 25^ fat, and 25^ carbohydrates, it will 

 be found that an uptake of 2,U2 liters of O2 corresponds to the combus- 

 tion of 1,6 g. of bacterial dry matter. Hence, 36O m^02 corresponds to 

 2U0 kg. bacterial dry matter, which is nearly one ton of live bacteria. 

 This gives us the order of food necessary to keep U/7 of the nematode 

 population of one hectare going for a year. 



I think that such calculations indicate that ecological considerations 

 of nematodes in the soil have a broad importance and, of course, there 

 is much that we do not know about the ecological factors of the soil and 

 their effects upon the various kinds of nematodes. 



