CONSERVATION g29 



veys of each region are necessary to formulate the proper measures to 

 control the insects. 



The size of the populations of rats, mice and many insect pests in- 

 creases with the size of cities and the correlated tendency toward the 

 development of slums in the older parts of the town. A survey in Eng- 

 land in 1953 reported that only 0.1 per cent of the houses in towns 

 with less than 25,000 houses were infested with bedbugs, but over 1.0 

 per cent were infested in towns with more than 100,000 houses! Careful 

 ecologic studies in Baltimore showed that although professional crews 

 of rat trappers might catch as much as half of the rat population, it 

 quickly returned to its former level. Cats proved to be much overrated 

 as rat predators and were not effective in controlling the rat popula- 

 tion. However, by changing the essential elements of the rats' habitat, 

 by improving sanitation, thus decreasing the garbage on which the rats 

 fed and the wastes in which they hid, the rat population was reduced 

 to about 10 per cent of its former size. It remained at this lower level 

 because that was the total number of rats which could survive in the 

 altered environment. 



374. Human Ecology 



No great amount of thought is required to realize that the ecologic 

 principles discussed in these pages apply to human populations as well 

 as to animals and plants. Human ecology deals not only with the dy- 

 namics of human populations but also with the relationship of man to 

 the many physical and biotic factors which impinge upon him. By re- 

 alizing that human populations are a part of larger units— of biotic 

 communities and ecosystems— man can deal with his own special prob- 

 lems more intelligently. Man has a great deal of control over his environ- 

 ment and has modified the communities and ecosystems of which he is 

 a part. However, this control is far from complete, and man must, like 

 other animals, adapt to those situations which he cannot change. By 

 understanding and cooperating with the various cycles of nature, man 

 has a better chance of surviving in the future than if he blindly attempts 

 to change and control them. 



There is a lively controversy at present as to whether the human 

 population is in danger of multiplying beyond the ability of the earth 

 to support it. In the past several centuries the population of the world 

 has increased tremendously as new territories have been opened for ex- 

 ploitation and as methods of food production have become more effi- 

 cient. Part of the disagreement involves the question of whether 

 comparable increases in the "carrying capacity" of the earth may be 

 expected in the future. There are many biologists and social scientists 

 who believe that the danger of overpopidation is both great and im- 

 minent, and others who hold the opposite view. It has been amply shown 

 that the Malthusian principle that populations have an inherent 

 ability to grow exponentially is true for organisms generally, and the 

 growth of the human population in the past three hundred years does 

 follow an exponential curve. W^hether other factors will come into play 



