Do archipelagoes really preserve fewer species than one island of the same total area.

The optimal strategy in the design of nature reserves is investigated by means of the theory of island biogeography. Some previous results are revised. A new form of the incidence functions is presented. Their merit is that they do not ignore the minimum area requirements, they are more flexible, and in a number of instances describe reality better than those formerly used. They lead to the conclusion that in order to preserve as many species as possible in refuges whose total size is given, the number of refuges must be limited and depends on the parameters of the incidence functions and on the area available.