Should nature reserves be large or small?

Abstract

Conservation of wildlife is one form of land use that competes with agriculture, forestry, urban development and outdoor recreation for an extremely limited supply of land. Conservationists are often faced with having to make decisions of priority, and the question arises as to whether it is better to have the area allocated for conservation in one large unit or in several smaller units. The scale of these units will vary both with different habitats and with different species being conserved: thus, in the tropics the area being considered is likely to be of the order of thousands of hectares, whereas in the industrialized world the areas may be only a few hectares in extent. The problem of how best to use limited resources becomes critical both to amateur conservation organizations (whose ‘shopping lists’ for reserves are long, but whose financial resources are limited by the extent of their charitable status) and to national organizations such as, in the UK, the Nature Conservancy Council (whose ability to support management agreements under Section 15 of the 1968 Countryside Act is limited by an overall budget). The question is: should such limited resources be devoted to the conservation of a few large sites or to two or three times as many smaller sites? The following argument shows that the proportional overlap of species is the critical factor, and data indicate that a number of small reserves have more species than a single large reserve.