6 



INTRODUCTION 



philosophical implications, is being given 

 more balanced consideration. 



The reahty and usefulness of the popu- 

 lation as an ecological unit were apparent to 

 us when we outlined the present book, and 

 our subsequent work has reinforced our 

 conviction of the importance of the prin- 

 ciples that center on the population. We 

 view the population system, whether intra- 

 species or interspecies, as a biological entity 

 of fundamental importance. This entity can 

 be studied with some measure of precision, 

 and the emergent principles are significant 

 throughout the field of ecology. The popu- 

 lation is forged by strong bonds with 

 autecology through the physiology and be- 

 havior of individuals; communities are 

 composed of recognizable population ele- 

 ments; and evolutionary ecology depends 

 directly upon population systems, since 

 selection acts upon populations that evolve 

 and become adapted to their environments, 

 to a more important degree than upon in- 

 dividuals. The study of populations as such, 

 as operational systems, yields principles 

 that clarify the nature of group interactions, 

 interactions that do not exist at the level 

 of the single organism, and that are too 

 complex at the community level to be 

 analyzed in a quantitative way. 



The major relations of animals center 

 around nourishment, reproduction and pro- 

 tection. The reaction to these needs may be 

 summarized by the concept of a "drive" to- 

 wards favorable ecological position. This 

 usually implies a drive for security of one 

 kind or another, or of all kinds. The par- 

 tially mystical idea of a "drive" hides the 

 nonmvstical one of the survival values fur- 

 nished by the attainment of nourishment, 

 protection and sufficient reproduction, or 

 even by the attempt to secure them. 



The situation can be clarified somewhat 

 by attending to only one of the three fun- 

 damental needs— protection, for example. 

 The given animal, or population, may orient 

 and move actively toward protected places 

 as a generalized reaction that may become 

 much more marked in times of particular 

 stress. Or the individual or population may 

 wander about, apparently at random, and 

 come to rest tmder favorable conditions. 

 Animals may invade a more stable physical 

 environment such as that furnished by a 

 pond or a forest, or in winter there may be 

 a movement down to the forest floor or an 

 active invasion of its superficial carpet of 



leaves and of the soil beneath them. Secu- 

 rity may be gained by attaining control of 

 a portion of the environment through the 

 slow processes of ecological succession 

 leading toward the estabhshment of an 

 ecological climax or through the more 

 active animals moving into natural safe 

 niches or building their own shelters. A 

 third mode of progress toward ecological 

 security, or more assured ecological posi- 

 tion, is found in societal evolution. These 

 are all aspects of the tendency toward eco- 

 logical homeostasis, and this sort of homeo- 

 stasy is one of the major inclusive principles 

 of ecology and, with a diflFerent emphasis, 

 of physiology as well. 



The tendency towards homeostasy ex- 

 tends through the diverse phases of ecology, 

 whether the subdivisions are based on habi- 

 tat differences such as those characteristic 

 of oceanography, of limnology, or of the 

 land, or of the living habitats of parasites. 

 Such tendencies are found under primarily 

 physical relations with nonliving environ- 

 ments and also when all the relations are 

 primarily biotic. 



The physical universe is indifferent to life 

 in general and resistant to the influence of 

 living organisms even in slow-working long- 

 time trends. For that matter, organisms are 

 largely indifferent to each other. Dramatic 

 incidents occur, and there is a strong tend- 

 ency to record and to overemphasize 

 these. Animals, under many conditions, and 

 plants as well, may merely persist; it is then 

 needful to search out the undramatic rela- 

 tions that allow them to continue to live 

 when little or nothing beyond mere exist- 

 ence is involved. Often only a saving few 

 individuals survive in a given habitat, and 

 these may spend much of their time appar- 

 ently doing nothing at all except remaining 

 alive. Hibernation, aestivation, "resting" 

 cysts, and resistant or so-called winter eggs 

 represent periods of marked quiescence. 

 The quiet retirement of animals capable of 

 extreme activity is often a fundamental part 

 of living. Hens fight and actively establish 

 social orders based on dominance and sub- 

 ordinance, yet they spend much more time 

 in which no activity is evident. Chimpan- 

 zees exhibit a strong drive for status in a 

 social group, and yet they too pass only a 

 small percentage of their time in active so- 

 cial tension. Outdoor nature is a place 

 where there is much inactivity. Even in the 

 teeming tropics an observer frequently has 



