Obviously, when a population of a particular species begins to multi- 

 ply, something has to give — and it does. Each piece of land has a limit 

 on the number of animals of any one species that it can support. Wildlife 

 biologists call this carrying capacity. It is the capability of an area to 

 provide a species' food, water, shelter, and other needs in a given 

 season. Once carrying capacity is reached, the surplus animals must 

 move elsewhere or die. If suitable under-stocked habitat is not available 

 within their range of mobility, the surplus animals are doomed. 



The tendency of populations of nearly all wild species is to expand 

 rapidly to the carrying capacity of the available habitat. In some species, 

 like pheasants and rabbits, which often produce ten or more young in a 

 single breeding season, this level can be attained very quickly, even by a 

 reduced breeding population. In other species, such as bears, which 

 rarely breed until they are several years of age and then produce fewer 

 young, the rate of increase is slower. But nature compensates by 

 endowing the slower reproducers with longer lives. 



For many species, particularly the smaller animals, nature's scheme is 

 to produce an overabundance of young. This increases the likelihood 

 that some will survive to perpetuate the species in spite of the inevitable 

 toll taken by adverse weather, disease, starvation, predators, and other 

 hazards. Most wild animals in North America produce all of their young 

 during a restricted season of a few weeks, usually in the spring or early 

 summer. In northern or temperate areas, summer carrying capacity is far 

 higher than that of winter because of the abundance of plant and other 

 life. A relatively small patch of cover may contain a population of a 

 dozen or more cottontail rabbits in early September, but few are likely 

 to survive until March. No more than 35 percent of the young mourning 

 doves produced in summer live until the next breeding season. The 

 higher the reproductive rate of a species, the higher its natural mortality 

 rate. In the wild, animals that produce many young have short Hves and 

 lose most of their young in their first year. 



Nature has many methods for regulating wild populations. One of 

 these is territorialism — the tendency of breeding animals to defend a 

 given area. Some sea birds nest almost shoulder to shoulder in dense 

 colonies, but they will not tolerate the presence of other birds within 

 reach of their nests. The lilting song of a male house wren is not a song 

 of joy, but a warning to all other wrens to keep away from his nesting 

 territory. If an intruder ventures too near, the defending male will attack 

 with righteous fury. A cock pheasant may gather a harem of six or more 

 mates and defend a crowing area approaching an acre or more. A male 

 grizzly bear, in breeding season, may defend 20 or more square miles 

 from all other males of his kind. 



Such natural population controls are nature's way of assuring that 

 only the stronger, quicker, and more alert animals of each species 

 survive until breeding season and perpetuate the species. 



At times, a series of mild winters and unusually favorable conditions 

 over several breeding seasons may temporarily raise the normal carrying 



