MULTIPLE-FACTOR AND SYNERGISTIC STRESSES 727 



maiden in a field. The unicorn would approach, and, when it was 

 lulled to sleep with its head in her lap, the hunters silently crept up 

 and carted away the helpless beast. Davenport (1897—1899), in his 

 classic two-volume work Experimental Morphology , summarized the 

 earlier literature dealing with the influence of environmental factors 

 on the form and function of biological material. He raised many 

 questions concerning physiological adaptation which are still unan- 

 swered today, e.g., the influence of multiple environmental factors 

 on organisms. Since the beginning of this century and especially since 

 the end of World War II, the volume of data dealing with the effects 

 of environmental parameters on organisms has been ever increasing. 

 Historically, many studies were restricted to investigating the 

 influence of a single factor on some organismic process. This 

 approach was logical, as it was simpler to vary only one factor at a 

 time rather than many simultaneously. Two problems that dis- 

 couraged multiple-factor studies were: (1) technological limitations 

 of equipment to control and selectively vary a number of factors and 

 (2) the underdeveloped state of the statistical and computer meth- 

 odology necessary to handle complex data. Although they have not 

 been completely resolved, these problems are less restrictive at 

 present. 



During the past 25 years, laboratory-oriented experimentalists 

 were not the only ones concerned with the influence of the 

 environment on organisms; field-oriented scientists also stressed the 

 probable importance of ecological interactions among organisms. 

 From this interfacing, the field of physiological ecology developed. It 

 is apparent that laboratory and field investigations must be combined 

 if we are to understand organismic— environmental interactions. 

 Many environmental questions are now decided in the courts, with 

 lavi^ers asking about the relevance of laboratory findings to what is 

 happening in the "real" world. To emphasize that the organism lives 

 in an environment consisting of many factors, each of which must be 

 considered, Billings (1952) reviewed the relationship between the 

 environmental complex and plants. He termed the view that an 

 organism exists in relationship to its entire environment the 

 holocoenotic approach to ecology. Figure 1 is a graphic representa- 

 tion of the interactive relationship between an aquatic animal and its 

 environment. The organism's ambient, or external, environment can 

 be divided into two major subdivisions, abiotic and biotic. Each of 

 these subdivisions includes a number of discrete factors, some of 

 which are indicated in Fig. 1. Obviously the organism is exposed to 

 many factors, each acting independently or in concert with others. 

 Coupling of abiotic and biotic factors can occur as readily as 



