FIG. 121 Model of a royal cell of the termite, showing differen 



castes. The queen ha 

 to the right. The k 



niarged abdomen; her head is turned 

 the left center. Two soldiers with 



pointed heads are in the upper right. Most of the rest 

 workers (courtesy Buffalo Society of Natural Sciences). 



though it was from the greater psychological potenti- 

 alities of primitive man that modern civilization arose 

 ( Alhe etal. 1949, Allee 1951). 



In these social relations, indeed in all sorts of 

 symbiotic relations between individuals, one or both 

 partners must have specialized behavior to effect and 

 maintain the relationship. Chemical stimuli are im- 

 portant in this respect and have received much study 

 to date but physical stimuli, such as color, shape, 

 texture, temperature, and so on may also have pri- 

 mary integrative importance as releasers for specific 

 behavior responses, the products of long evolution 

 (Davenport 1955). 



MUTUALISM 



Mutualism is an association between two 

 or more species in which all derive benefit in feeding 

 or in some other way. The term symbiosis has often 

 been applied to this relationship, but symbiosis prop- 

 erly refers to the intimate association of two or more 



dissimilar organisms, regardless of benefits or the 

 lack of them, and hence includes mutualism, com- 

 mensalism, and parasitism. 



Mutualism, as is true also with commensalism 

 and parasitism, may be facultative, when the species 

 involved are capable of existence independent of one 

 another, or obligativc, when the relationship is im- 

 perative to the existence of one or both species. Con- 

 siderable study and experimentation is sometimes re- 

 quired to decide whether a particular relationship is 

 facultative or obligative, or even whether it is truly 

 mutualistic. Mutualism is sometimes considered as, 

 fundamentally, reciprocal parasitism. Many examples 

 of ecological interest of mutualism, commensalism, 

 and parasitism are cited by Pearse (1939) and Allee 

 et al. (1949) ; only a few will be given here. 



Mutualism in plants is demonstrated in the asso- 

 ciations of fungi and algae to form lichens, of nitro- 

 gen-fixing bacteria with the roots of legumes, and of 

 fungal mycorrhizae with the roots of many flowering 

 plants. 



176 Ecological processes and dynamics 



