RELATIONS WITHIN A SPECIES 



349 



reproductive 

 type 



fecundity 



reproductive 

 periodicity 



fertility 



total 

 environment 



environmental 

 ges 



BIOTIC POTENTIAL 



~\ ^ Chan 



ENVIRONMENTAL RESISTANCE 



REPRODUCTIVE 

 RATE 



POPULATION 

 GROWTH RATE 



# 

 ^ 



CARRYING 

 CAPACITY 



POPULATION 

 SIZE 



♦ 



FACTORS CAUSING 

 CYCLES 



SPATIAL 

 RELATIONS 



RACIAL 

 SENESCENCE 



EXTINCTION 



Figure 18.2 Interrelationships among factors contributing to population size — a summary of the 

 more important phenomena of population dynomics. 



ample, animal B might dominate animal C and be 

 dominated by animal A, but animal C might domi- 

 nate animal A. 



Social division of labor is a phenomenon in 

 which each individual of a society performs one of 

 several possible separate functions. This social re- 

 lationship is limited to colonial organisms and to 

 complex societies. An example of colonial division 

 of labor is found in certain coelenterates; the Portu- 

 guese man-of-war is a colony made up of reproduc- 

 tive, feeding, and protective individuals. Among 

 complex societies the most intricate divisions of 

 labor are in caste societies. For example, in ter- 

 mites each kind of individual not only performs a 

 separate function but also is specialized structurally 

 to perform these functions. Where caste societies 

 have the most unique-looking types of individuals, 

 there is also the most nearly absolute dominance by 

 single individuals; the reproductives, especially the 

 queen, dominate the activities of all other members 

 of the caste society. 



There are both advantages and disadvantages to 

 social behavior. The advantages exist from individual 

 eflfort's benefiting the entire group or the group's 

 benefiting the individual. A society benefits when a 

 single animal locates food and other necessities, or 

 danger. Benefits from unified activity include co- 



operative defense and predation, greater likelihood of 

 mating, and control of environmental extremes. An 

 example of environmental control is found in bees 

 which beat their wings to reduce temperature or 

 group together to prevent the hive's freezing. The 

 main disadvantages of social behavior are greater 

 possibility of disease and parasitism transmission, of 

 predator attraction, and of food depletion. 



Societies contribute to all of the population phe- 

 nomena discussed. Their relationship to the local 

 occurrence of species is especially significant. So- 

 cieties are by their very nature examples of clumping; 

 however, individual societies might in turn be ran- 

 dom, even spaced, or clumped. Also, mobile societies 

 (bands) cause local spatial relationships to fluctuate; 

 when societies are moving, it is possible for spacing to 

 assume any of the three types at diflTerent times. 



SELECTED READINGS* 



Allee, W. C, 1931. Animal Aggregations, a Study in General 

 Sociology. University of Chicago Press, Chicago. 



. 1951. The Social Life of Animals. Beacon Press. 



Boston. 



•See also the General Ecol()i»y References, p. 3.^8. 



