ROLE OF MAMMALS IN THE ECOSYSTEM 



Mammals have a major role in their communities, primarily in the transfer of 

 energy and nutrients through food chains. As a result of their role mammals 

 can sometimes exert significant influences on other groups within their 

 communities. Herbivores may assist in the distribution of plants by 

 disseminating seeds or limit the distribution of other plants by overutilizing 

 them. Carnivores may influence the abundance of their prey and beavers can 

 alter entire communities to their liking. Knowledge of the food habits of 

 mammals is important for an understanding of the effects of people on mammals, 

 because people can affect mammals indirectly through their food supply. For 

 example, spraying a forest stand to control spruce budworm may reduce 

 populations of other insects that serve as food for small mammals. 



Mammals found within the characterization area range from strict herbivores 

 (e.g., deer, moose, snowshoe hares), which consume only plant material, to 

 insectivores (e.g., bats and shrews), and carnivores (e.g., bobcat and otter) 

 that rely solely on invertebrates or meat, respectively. The majority of 

 species, however, are omnivorous; that is, they consume both plant and animal 

 matter. The food preferences of the mammals found in coastal Maine are shown 

 in figure 17-3. The role of herbivores is to convert the energy stored in 

 plants into animal tissue. Mammals that consume twigs, stems, and bark (e.g., 

 deer, moose, hares) have special adaptations in their digestive systems (rumen 

 or large caeca) and host symbiotic microorganisms that aid the breakdown of 

 complex structural carbohydrates (cellulose and lignin) and release the energy 

 stored in chemical bonds. Other herbivores do not possess this ability and 

 consume more digestible plant material, such a fruits, seeds, nuts, leaves, 

 and tender shoots. 



Usually only a relatively small amount of the total plant material in a 

 community is consumed by mammals. Browsing mammals can kill individual 

 plants by repeated cropping of twigs, stems, and foliage. For example, heavy 

 browsing by deer on Canada yew has virtually eliminated this plant from 

 portions of its former range in New York. In the northern hardwood forests of 

 the Adirondack Mountains, deer have caused a shift in the plant species 

 composition by selectively browsing maple, birch, and ash seedlings, which 

 allowed the less desirable beech to become dominant in the understory (Tierson 

 et al. 1966). Areas protected from deer had a more even distribution of plant 

 species. Herbaceous vegetation showed similar effect. Biologists have 

 recognized the ability of certain plants, such as mountain maple, to withstand 

 repeated cropping of current growth and still survive. These plants can be 

 encouraged where food production for browsing animals is desired. 



Small mammals can affect the regeneration of plants by eating seeds or nuts. 

 Squirrels can consume the entire crop of acorns or hickory nuts in most years. 

 However, during the occasional years with "bumper" crops, enough seeds escape 

 to ensure sufficient regeneration (Barnett 1977). 



Sometimes mammals aid the dispersal of plants by consuming fruits and later 

 passing the seeds in their feces. In the characterization area, bears, 

 raccoons, foxes, and other mammals distribute the seeds of such plants as 

 raspberries and cherries in their feces and beggars ticks in their fur. 

 Recent research in New Hampshire suggests that gray squirrels are perhaps the 

 most important factor affecting establishment of white pine regeneration 



17-12 



