Ch. 5— Maintaining Biological Diversity Onsite • 105 



ment of an ecosystem's contribution to diver- 

 sity, its vulnerability, and its social and eco- 

 nomic significance. 



Design off Protected Areas 



The sizes and locations of protected areas are 

 determined first by political and financial con- 

 straints. Within those limits, the designs of na- 

 ture reserves have usually been based on natu- 

 ral history characteristics of the particular 

 species of greatest interest. Recently, however, 

 scientists have begun to develop theories for 

 designing nature reserves to optimize protec- 

 tion of biological diversity rather than protec- 

 tion of particular species. These theories are 

 still based mainly on inferences from general 

 scientific principles and are largely untested. 

 Thus, they are the subject of much academic 

 debate among scientists (53]. 



Criteria for optimum size and shape for pro- 

 tected areas have been based on information 

 from insular ecology (e.g., refs. 15,16,74,90). 

 These criteria, however, are widely viewed as 

 too simplistic, and the theories are being fur- 

 ther developed with information from ecolog- 

 ical-evolutionary genetics (24,70,73,79) and 

 from theoretical population dynamics (28,74, 

 80). These theories focus mainly on terrestrial 

 protected areas and probably have limited use 

 for the design of coastal-marine reserves. The 

 great dispersive abilities of marine organisms 

 and the interconnections of adjacent commu- 

 nities thus complicate decisions concerning the 

 proper size and spacing of reserves. (See box 

 5-A for discussion contrasting terrestrial and 

 coastal-marine systems.) 



Islands and Boundaries 



Information on the occurrence and natural 

 distribution of species on islands has been used 

 to formulate theoretical size and location cri- 

 teria for protected areas intended to maintain 

 diversity. The equilibrium theory of island bio- 

 geography (52) maintains that greater numbers 

 of species are found on larger islands because 



Box 5-A. — Differences Between 

 Terrestrial and Coastal-Marine Systems 



It is difficult to gauge the relative differences 

 in biological diversity in terrestrial and 

 coastal-marine environments. Dry land con- 

 tains approximately four times the number of 

 species found in the sea; on that considera- 

 tion alone, terrestrial ecosystems seem in- 

 herently more diverse. Differences in faunal 

 diversity between marine and terrestrial envi- 

 ronments are primarily due to insects. With- 

 out them, marine fauna would be more diverse 

 than terrestrial fauna. However, terrestrial 

 flora clearly exhibit greater diversity than ma- 

 rine flora (51). 



Viewed from a different perspective, in 

 which the number of higher taxa (particularly 

 animal) indicate degree of diversity, the sea 

 would appear more diverse because many 

 higher taxa (i.e., phyla, classes, orders) are ex- 

 clusively marine. Implicit in this view is the 

 notion that higher levels reflect greater genetic 

 differences— i.e., a single species may be the 

 sole representative of an order, class, or phy- 

 lum, and the loss of one of these species might 

 cause a far greater genetic loss than would the 

 loss of a species in a taxon made up of several 

 hundred or thousand members (51). 



Another difference is that many fish and in- 

 vertebrates that make up the bulk of marine 

 species pass through several life stages from 

 egg to adult. In many of the life stages, the 

 organisms seem unrelated to that of the adult 

 form. These different forms can live in differ- 

 ent ecosystems or in distinctly different niches 

 within the same ecosystem. Maintaining one 

 species may therefore require maintenance of 

 several different ecosystems (51). 



Movement of organisms and materials be- 

 tween different community types — seagrass, 

 coral reef, and mangrove— means that terres- 

 trial and marine communities sometimes can- 

 not be defined simply by their physical bound- 

 aries. Effectiveness of efforts to protect one 

 community type may be diminished by fail- 

 ure to protect neighboring communities as 

 well as adjacent watersheds (40). 



