The Critical Environment 5 



a sea-bird rookery (Fig. 1.2). In other situations the effects of the 

 presence of other animals and plants are more subtle. Although such 

 influences cannot be photographed, they are often just as crucial, and 

 the environment must be imderstood to include both physical and 

 biological influences whether conspicuous or obscure. 



Allan D. Cruichihank, National Audubon Society 



Fig. 1.2. Gannet rookery on Bonaventure Island, Quebec, showing the keen 

 competition for nest sites. 



The Critical Environment 



Are the necessary dealings of the organism with the environment 

 usually successful? Can all living things find their needs in the out- 

 side world and avoid dangers? In most instances a large fraction of 

 the young plants and animals produced are unable to cope with the 

 environment, and relatively few survive. A striking example of the 

 magnitude of natural mortality is found in the accompanying data 

 from a study of the growth of mackerel eggs and young off the east 

 coast of the United States (Sette, 1943). 



Stage of Young Mackerel Duration Mortality 



Spawning to 10-mm length 40 days 14% per day 



Transition to post-larva few days 30% per day 



Post-larva to 50-mm length 40 days 10%, per day 



