Best shape for nature reserves

Abstract

The ideas of classical island biogeography¹ have been used^2–6 to derive rules for the optimal design strategy for nature reserves. For example, Diamond³ states that, given limited (financial) resources, it is better to purchase a few large reserves rather than many small ones of equal total area; and that reserves should be as close to one another as possible. The validity of some of these rules has, however, been questioned^7–10; for example it has recently been shown^9,10 that several small reserves may contain more species than a single one of equivalent area. These rules have nevertheless been accepted uncritically by others, including the IUCN¹¹. Here, I examine Diamond's rule³ that reserves should be as round as possible and conclude that in certain circumstances the optimal shape may be other than circular. There is no a priori reason for believing that these circumstances are unrealistic, and I know of no observational evidence to suggest whether they are found in nature or not. I also reason that the rule that reserves should be as close to each other as possible is inconsistent with the statement that they should be circular.