RELATIONS WITHIN A SPECIES 



343 



nent exit from a locality, and immigration is the 

 permanent entrance into a new area. 



HOME RANGES AND TERRITORIES 



These two spatial relationships are different de- 

 grees of the same phenomenon, the space occupied 

 by an animal. The major difference between the 

 two is in the matter of defense of the space; only 

 territories are defended. A home range, is the area 

 covered by an animal in its normal activities. It 

 possesses a degree of permanence and does not exist 

 for completely nomadic species. Although most 

 animals have some sort of home range, only a few 

 actively defend an area and therefore have a 

 territory. Territoriality is most common in verte- 

 brates, especially birds and mammals, but is also 

 fairly well developed in some fishes and reptiles. A 

 few amphibians display rudimentary territorial be- 

 havior, and among invertebrates (especially certain 

 insects, crustaceans, spiders, and moUusks) territori- 

 ality can be found in a number of groups. 



Home ranges and territories also differ in that 

 home ranges are used for all life processes whereas 

 territories are frequently specialized, many different 

 territories being defended for somewhat specific ac- 

 tivities. For example, birds often have many sea- 

 sonal territories. During the breeding season dif- 

 ferent species of birds may have either a single ter- 

 ritory for mating, nesting, and feeding; one mating 

 and nesting territory and one feeding territory; or 

 three distinct territories — mating, nesting, and feed- 

 ing. Also, during the nonbreeding season birds may 

 have one or more territories for feeding, daytime 

 roosting, nighttime roosting, and other functions. 



Although individual home ranges and territories of 

 members of the same species vary in shape, area, and 

 location, the main function of both spatial relation- 

 ships is protection. The establishment of either 

 allows greater efficiency in the individual animal's 

 food getting, escape from predators, and other criti- 

 cal processes. In some cases additional protection 

 exists because the animals construct burrows or other 

 shelters. Territories generally provide greater pro- 

 tection than do home ranges. For example, in birds 

 territoriality reduces actual fighting for breeding 

 sites; guarantees food, cover, and nesting materials; 

 protects the nest, young, and mates; prevents over- 

 population; and acts as a means of instigating the 

 sexual bond. In addition, the effectiveness of both 



home ranges and territories is a function of popula- 

 tion fluctuations. As populations increase in numbers 

 both territories and home ranges are contracted 

 toward a minimal size; and there often is a greater 

 than normal number of individuals with no set home 

 range or territory. These nomads wander through 

 the unoccupied space that exists among territories. 

 The consequences of overpopulation, then, are 

 greater contact among individuals of restricted terri- 

 tories and/or nomads and greater stress, especially 

 where territoriality is a strong instinctive behavior 

 pattern. 



MIGRATION 



Interarea movements fall into three categories, 

 metamorphic, daily, and annual. Melamorphic migra- 

 tions must include the change of form from an 

 immature stage to the adult. These movements com- 

 monly occur in many groups in which the adults are 

 terrestrial, e.g., certain amphibians and insects, and 

 the immature stages are aquatic. Daily migrations are 

 interarea movements, often associated with the daily 

 cycle of light and darkness. Oceanic and lake plank- 

 ton, tidepool animals, and many land animals are in 

 areas of semidarkness during daylight hours and are 

 near the surface of water or active in the open dur- 

 ing the night. 



Annual migrations, often simply called "migrations," 

 are movements between areas in which one journey 

 is made during a certain portion of the year and the 

 other during another portion. Such migrations tend 

 to be further classified in reference to the amount or 

 kind of space traversed, as latitudinal (north-south), 

 altitudmal (in reference to mountains and valleys), 

 and /oca/ (limited in distance and not necessarily as- 

 sociated with either latitude or altitude). However, 

 migration still is a study of almost meaningless con- 

 trasts. Perhaps this confusion comes from attempts to 

 explain all migration, even that within single groups 

 of animals, in the same terms. When this is tried, 

 each new hopeful explanation of cause and effect 

 tends to be negated by further investigations of other 

 members of the same large taxon. 



VERTEBRATE VARIATIONS 



The migration of birds presents the best example 

 of the problems that arise in attempts to explain this 



