350 Relations within the Species 



oysters, mussels, and other sessile animals growing on substrata of 

 limited dimensions; a few individuals, growing faster than the rest, 

 gain the upper hand and smother their more retarded brothers. This 

 automatic reduction of the population by the growth of its own mem- 

 bers produces at least the minimum spacing necessary for survival, 

 but it usually does not provide the most favorable spacing for the best 

 development of the individuals. Man can often improve growing 

 conditions for particular species in which he has a special interest by 

 further thinning— and this is done regularly, of course, by professional 

 growers, such as oystermen, farmers, and foresters. 



For motile animals the danger exists that during favorable condi- 

 tions the members of a species inhabiting a region will move too close 

 together, with the result that wholesale destruction will take place 

 when conditions become unfavorable again. In some species we find 

 an instinctive reaction causing the animals to space themselves out to 

 a certain extent at least; and the existence of this response helps to 

 avoid overcrowding, as will be discussed in the ensuing section. 



Home Range and Territory 



Many kinds of animals are known to establish a center of opera- 

 tions for themselves and to confine their roamings within certain 

 boundaries. The area within which an animal tends to stay is known 

 as its home range. Sometimes other members of the same species 

 are not allowed to enter the area, or a portion of it, and any trespassers 

 are forcibly driven out. The inner sanctum that is actively defended 

 is called the animal's territory. The territory may be established by a 

 social group, such as a hive of bees or a colony of ants, by a breeding 

 pair, or sometimes by a single individual. The existence of territories 

 with "exclusive rights" was recognized in an old Chinese proverb 

 that states: "One hill cannot shelter two tigers." A dog's own yard 

 is his territory, and he drives other dogs out with a self-assurance that 

 is familiar to all of us. Within their own territories animals typically 

 acquire a heightened position of dominance in relation to other mem- 

 bers of the same species. 



The concept of territory was first delineated for birds. It was ob- 

 served that in many species each male established a territory at the 

 beginning of the breeding season. The male then isolates himself, 

 and confines his movements to his own territory He becomes hostile 

 to other males of the same species, with which he was on amicable 

 terms only a short time previously. This bird drives others of his kind 

 out of his territory, but pays little or no attention to birds of other 



