1972 and cultivated land increased during the same period from 18% to 83%.^ From 

 the I960 to the 1970 census, land use for settlement increased faster than the 

 population in 82% of U.S. communities.'* Environmental management that has as its 

 goal securing, restoring, reclaiming, and protecting fish and wildlife habitat is more 

 critical today than ever before, because of mounting pressure on potential habitat 

 from both the increasing human population and the escalating demands of society. 

 Continuation of present land-use trends may result in substantial loss of species and 

 genetic resources within the next few decades.- Environmental awareness, concern, 

 and appropriate management may help to ensure that future losses are not entirely by 

 default. 



Although appropriate management might facilitate such things as the introduction 

 or re-entry of desired animals, species protection without habitat preservation is 

 unworkable, except in very short-term, unstable situations. Various habitats provide 

 refugia both for animals which are available for recolonization of disturbed areas and 

 for backcrossing with other stocks. Protected habitats may also serve as templates 

 that can be used in returning disturbed areas to more natural states. 



Ecosystems (systems of organisms and their respective habitats) are characterized 

 by interrelationships among species and by balances in all aspects, not by any one in 

 particular (Figure 1).' Protection could foster the maintenance of dynamic relations 

 within and among ecosystems. This should contribute to their long-term persistence 

 (Figure 2).^''>* Although highly complex and diverse systems are usually considered 

 to be more stable than simple ones, large and unprecedented perturbations imposed 

 by man may prove more detrimental to complex natural systems than to those which 

 are simple.^ Often the adaptedness and stability of an ecosystem are disturbed by 

 man's intervention. This may necessitate further intervention. In addition to 



Figure 1. Schematic representation of an ecosystem, charac- 

 terized by balances in all aspects, not by any one in par- 

 ticular. ^ 



59 



