350 W. H. PEARSALL 



poaching prevalent there, and if this is eHminated I should be surprised if it 

 were not possible to harvest much more than 5 per cent of the present 

 population without reducing the gross numbers. It must, of course, be 

 recognized that the balance of predators to herbivores v^ill also need super- 

 vision as in effect any method of harvesting simply substitutes a human 

 predator for a wild animal. 



ECOLOGY OF PROTEIN PRODUCTION 



Both the harvesting of game as human food and the provision of tourist 

 facilities would help to justify the maintenance of national parks as a form 

 of land use. Nature conservation of this type in East Africa is scientifically 

 justifiable on much stronger economic grounds. We want to know, before 

 they are destroyed, how these eco-systems work and remain productive 

 under adverse and arid conditions. 



Their productivity is, of course, a balance between two things: 



(i) The primary productivity — the amount of energy (sunlight) which can 

 be fixed by plants in the form of dry matter and especially of protein, 

 (ii) The conversion ratios — how much of the primary production can then 

 be got into the form of herbivorous animal or higher. 



The losses in both cases seem to be tremendous, and in conclusion, a brief 

 consideration of these subjects may be of value. 



Primary production in the Serengeti depends very much on water and 

 this in turn means getting the water into the soil as Perriera (1954) has shown. 

 Low soil temperatures (due to a sufficient shade from vegetation) and a good 

 soil texture (associated vnth the above and with a rather unknown effect due 

 to the incorporation of vegetable residues into the soil surface) largely 

 determine whether the rain penetrates or runs off on the surface, leading to 

 soil erosion. 



Any form of extreme destruction of the vegetation cover is thus harmful 

 to the water relations and the common statement that East Africa is drying 

 up is true in as far as it describes the widespread results of over-grazing and 

 over-burning. 



The second important feature of a protein-producing system is the 

 conservation of nitrogen, the element drawn from the soil in largest propor- 

 tion. Much energy is used in converting gaseous nitrogen into organic 

 forms, and when so converted it should be conserved. To burn the vegetation 

 doing the conversion and containing the converted nitrogen — the protein — 

 usually results in diminishing the proportion of nitrogen in the nitrogen 

 cycle by more than can be taken out in the form of a protein crop. Never- 

 theless fire is almost always used in African pastoral economies — so much 



