each of the three Wildlife Management Units along the coast. These data were 

 obtained from species management plans, described earlier, and are 

 approximations at best. The data concerning animal densities, in particular, 

 should be considered only as very rough approximations, and only be used for 

 comparing relative abundance between regions. More detailed data are 

 available in appendix tables 1 to 9. In most instances the density figures 

 are different for each of the three units, because the total habitat figure is 

 made up of differing amounts of habitat types, each with a corresponding 

 density figure. Also, animal abundance in the same habitat may vary from one 

 unit to the next, because of the quality of the habitat, its interspersion 

 with other required types, its positon in the species range, or other factors 

 described below. 



Natural Factors Affecting Abundance 



A unit of habitat is capable of supporting only a given number of individuals 

 of one species. This is often called the carrying capacity of the habitat. 

 The size of a population results from increases due to birth and immigration 

 and losses due to death or emigration. For populations below carrying 

 capacity, gains usually exceed losses and the population increases. As it 

 approaches saturation levels, several factors can enter to reduce population 

 growth by affecting reproductive rates, increasing mortality, or increasing 

 emigration. 



Each species has a maximum inherent reproductive rate, which is determined by 

 (1) the number of young per litter, (2) the number of litters per year, and 

 (3) the minimum age of first breeding (appendix table 11). Some species 

 (e.g., bats, black bears) have low rates of reproduction, producing only one 

 or a few young each year. Others, like the meadow vole, are capable of 

 producing up to 40 to 50 young in a single year. Species with high 

 reproductive potentials are capable of rapid population increases following 

 depletion of their numbers or upon encountering unoccupied habitats. 

 Conversely, species with low reproductive rates will rebound slowly from 

 reductions in population size and are therefore more susceptible to 

 exploitation. 



Reproductive rates may be reduced to a level lower than their maximum 

 potential by inadequate nutrition. Deer on poor range have a lower incidence 

 of twins or triplets, and first year does on poor range are less likely to 

 produce fawns than deer on good range. Snowshoe hares, mice, and voles may 

 have fewer litters per season, as well as a delay until first breeding, due to 

 food shortage. Social stress, brought about by high population densities, may 

 have similar consequences. The mechanics of stress are not entirely clear, 

 but apparently, increased contacts between individuals causes changes in 

 hormone levels that in turn affect reproduction. 



Territorial behavior also limits the density of animals in a given unit of 

 habitat. Many species, including mice, beavers, and most carnivores, are 

 territorial and individuals exclude other members of their species from the 

 particular area they occupy. This limits population size by (1) spacing out 

 individuals, (2) reducing immigration, and (3) preventing some individuals 

 from breeding. Young produced within a territory are tolerated until they 

 become independent, at which time they are forced to disperse. If these 



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