NO. 3597 RODENT ETHOLOGY — EISENBERG 29 



Discussion. — As stated in the introduction to this section, rodent 

 social systems may be classified as solitary, pair tolerance, and com- 

 munal. The latter two represent in extreme form a closed social 

 grouping, impermeable to outsiders. In reality there are rodent 

 species that, as species, exhibit so-called loose social systems wherein 

 the species may oscillate between a more dispersed soUtary formation 

 or a more tolerant, semicommunal system — depending upon the en- 

 vironmental conditions and the population density. The data from 

 the current studies permit me to attempt several generalizations cast 

 against the background of this social classification. 



First, it appears that what separates a socially tolerant from a 

 solitary species is the ability of the former to overcome an initially 

 agonistic or avoidance interaction by means of special behavioral 

 mechanisms to insure contact and familiarity without the danger of 

 fighting. Among these mechanisms grooming appears to be impor- 

 tant. Fm"thermore, a social species can achieve contact in the absence 

 of primary sexual stimuli. A solitary species is either unable to 

 achieve contact or, if it does, it is stressed to some extent; and, under 

 conditions of prolonged contact, the physiological mechanisms 

 governing the reproductive capacity break down. This difference 

 between the extreme forms of solitary and social species is not viewed 

 as absolute but rather as a result of differences in sensitivity to 

 contact. Table 23 summarizes this concept whereby the same phys- 

 iological pathologies are considered for each major social type. 



A second generalization concerns the probable outcome of the 

 various social tests if applied to a species of each major social type. 

 Table 24 summarizes these predictions, which are drawn from the 

 data in the previous section. In table 25 the species included in 

 this study are ranked as to social tolerance according to the field and 

 laboratory data. 



General Discussion 



The behavioral survey of the present study group has shown 

 considerable uniformity in the orientation movements and fLxed 

 action patterns. Definite differences in fixed action patterns are 

 usually correlated with corresponding differences in morphology as, 

 for example, in bipedal locomotion. Even in such a markedly 

 specialized behavior pattern, normally quadrupedal species have the 

 capacity to assume a bipedal stance and even hop for a short distance. 

 When we consider sandbathing as a fixed action pattern, we find 

 that it is composed of two to three distinct movements that are part 

 of the behavioral inventory of almost all mammals, and only a unique 

 combination of these components results in a species- or taxon- 

 specific behavior. 



