706 • Technologies To Maintain Biological Diversity 



the populations on smaller islands are more vul- 

 nerable to extinction. That vulnerability is due 

 to probabilistic nature of individual births, 

 deaths, occurrences of disease, and changes in 

 habitats. Also, islands farther from continents 

 have fewer species, because colonists from 

 large land masses are less likely to reach them. 

 This theory was extended from true islands to 

 their terrestrial analogs (e.g., forest patches in 

 agricultural or suburban areas), and the field 

 of study become known as "insular ecology" 

 to reflect this broader perspective. Scientists 

 do not concur that the theory accurately ex- 

 plains natural patterns of species diversity, and 

 research has been initiated to test the theory. 

 (See Gilbert (27) and Simberloff (76) for reviews 

 of studies that confirm or refute the equilibrium 

 theory.) In any case, the island analogy— that 

 much of the natural diversity is being reduced 

 and confined to small, often isolated areas— is 

 not in dispute. 



Nature reserves serve as islands for species 

 incapable of surviving in human-dominated 

 habitats. Isolated natural areas are likely to 

 experience declining numbers of species when 

 their size is reduced by deforestation or similar 

 habitat changes. The analogy between islands 

 and nature reserves was reinforced by findings 

 from some of the early tests of equilibrium the- 

 ory. These findings led to proposed design cri- 

 teria for nature reserves intended to minimize 

 the loss of species over time (53). The designs 

 called for large nature reserves near each other, 

 to reduce the effects of small areas and dis- 

 tances on species survival. Other design ele- 

 ments not explicitly derived from equilibrium 

 theory but thought to maintain a greater num- 

 ber of species at equilibrium also exist. How- 

 ever, these are rather academic "all other things 

 being equal" principles, and on the ground, 

 complex habitat differences among areas should 

 weigh more heavily in pragmatic choices of 

 which sites to conserve. 



The applicability of insular ecology to con- 

 servation is being tested by the World Wildlife 

 Fund's Minimum Critical Size of Ecosystems 

 Project (49). Biologists took inventories of plant 

 and animal life in an Amazon forest area be- 

 fore it was fragmented by development. Vari- 



ous-sized patches of forest were kept intact 

 through coordination with the deforestation 

 and development program, and biologists now 

 monitor plant and animal populations in each 

 patch. Although the project is only 20 years old, 

 changes in the biota are already evident (47,48). 



The guidelines for optimum biological design 

 still have many limitations (72). Most of the rele- 

 vant research has focused on animals, particu- 

 larly forest-dwelling birds; too little research 

 has been conducted on plants or on other types 



Photo credit: R.O. Bierregaard. Jr. 



The Minimum Critical Size of Ecosystems Project 

 (above) of the World Wildlife Fund and Brazil's National 

 Institute for Amazon Research is a long-term study of 

 the effects of fragmentation on the Amazon forest as it 

 is cleared to create pasture. This study is providing data 

 on which to base design and management recommen- 

 dations for national paries and reserves of particular 

 relevance to the Amazon forest. 



