ECONOMIC PROBLEMS 87 



An analogous method is used for the control of pest 

 plants, and has been used successfully for prickly pear 

 and Lantana (Imms, 1931). The relation of insects 

 to flowers is of great importance in horticulture and 

 more especially in fruit orchards. In some cases the 

 density of blossom is too great to allow of complete 

 fertilization by the natural insect polhnator popula- 

 tion, and bee-hives are planted at intervals to 

 supplement the other insects. 



When we come to conservation the practical prob- 

 lems turn to a large degree on fluctuations in num- 

 bers and on the maintenance of something approaching 

 an optimum population. The aim of most ecological 

 studies of game birds, wild mammals, etc., is to find 

 some means of eliminating fluctuations and maintain- 

 ing as high a density of numbers as is practicable 

 without leading to disastrous reduction, e.g. through 

 epidemics. The same aim is inherent in the fishery 

 research. It is clear here that the concepts of animal 

 numbers that are now emerging from ecological 

 research have a most important bearing on these 

 problems. 



It will be clear that there is a difficulty in present- 

 ing in a small space a balanced account of economic 

 ecology, since each of the subjects touched upon 

 would fill an encyclopaedia. The situation may be 

 summed up by sa3dng that most economic biological 

 problems deal with numbers of animals, and often 

 with fluctuations in numbers and the inter-relations 

 of different species of animals. Animal ecology is 

 buflding up from basic surveys a science whose 

 aim is the complete analysis of animal behaviour, 

 numbers, and distribution. It has only recently 

 progressed far enough to make close contact with the 

 economic problems. It still has a long way to go. 



