The Interdependence of Living Things 152 



ever, is quite out of the question for the common plants and 

 animals as we know them today. However the situation 

 has come about, they are now both as individuals and as 

 groups completely enmeshed in the lives of one another. 



The multiplication of any one species is definitely 

 limited by the existence or absence of other species. As the 

 season advances, there is a daily fluctuation in the propor- 

 tions of the inhabitants of the soil and of the water. A few 

 cloudy days will diminish the growth of certain plants and 

 reduce the available food for some of the animals. Rapid 

 growth of some seedlings will increase the shade over some 

 square feet of soil and prevent the growth of other plants. 

 Anyone who has been confronted with the weeding of a 

 garden will know how much faster some plants can grow 

 than others and how the growth of some interferes with 

 the growth of others. This is not merely a question of oc- 

 cupying space. It is also a question of modifying the soil 

 chemically either by removing from it or putting into it 

 substances which are effective either to promote or retard the 

 growth of others. As vegetable life increases more and more, 

 animal life also increases, both as to numbers of species and 

 as to numbers of individuals. 



Animals come in conflict with one another in various 

 ways. One species may compete with another in utilizing 

 a limited amount of food. Each animal is exposed to the 

 predacious activities of others. The birds seem to have an 

 uncanny knack of finding insects where most of us would 

 never see them. The more birds there are the fewer insects 

 will there be in a given area. Adaptation of birds to see in- 

 sects is met by counter-adaptation of insects to escape being 

 seen: both cannot be perfect. The frog's eggs eventually 

 become tadpoles and the tadpoles eventually become young 

 frogs, hopping onto the land, where they change their diet. 

 A perfectly adapted frog will capture every insect which 

 comes within several inches of its snout. A perfectly adapted 

 insect will escape every attempt of the frog to capture it. A 

 perfectly adapted bird or snake will capture every frog to- 



