Protected Areas and Species

Protected areas are widely recognized for their value in the conservation of biodiversity. Their establishment and management sometimes impose costs, however, such as the direct cost of protection and management activities and the opportunity cost to local residents who have to forego natural resource extraction. It is therefore essential that the creation of protected areas be planned systematically to ensure that costs are minimized and benefits maximized. This entails setting targets for the overall set of features that should ideally be conserved through protected areas and defining parameters to assess current protected-area networks and guide their expansion (Margules & Pressey 2000). The Fifth World Parks Congress (WPC, September 2003, Durban, South Africa, http://iucn.org/themes/wcpa/ wpc2003/) provided fertile ground for the discussion of targets for biodiversity conservation planning, particularly through Workshop Stream 7 on “Building Comprehensive Protected Area Systems. ” Here, we build on these discussions to argue that, despite a range of shortcomings, species data provide the best basis for setting these targets. Setting targets for protected-area planning is not a trivial task because biodiversity represents a continuum of ecological organization that cannot be encapsulated in a single variable. Conservation planning is, in part, a spatial exercise; hence, only biodiversity features that can be mapped are of practical value for this purpose. Techniques for mapping and measuring ecological and evolutionary processes are in their infancy (Cowling et al. 1999), and conservation planning has therefore focused mainly on biodiversity pattern. The types of biodiversity features most commonly used in conservation planning are species and broad-scale attributes obtained from data on species communities and/or abiotic data. Different biodiversity currencies have different advantages and problems. There is an inevitable tradeoff between biological detail and data availability. Maps of abiotic information (e.g., temperature, geology, relief ) and of habitats and vegetation classes are now widely available at fine resolution, particularly with the improvement in remotesensing techniques in the past few decades (Turner et al. 2003). Data on species distributions, on the other hand, are still mainly limited to the best-known taxa—particularly vertebrates and vascular plants— a very small fraction of the planet’s species. Species data sets are furthermore plagued by biases in sampling effort (Nelson et al. 1990). Data availability alone would therefore support the use of broad-scale biodiversity attributes. Broad-scale biodiversity features, however, suffer from several fundamental drawbacks. First, they are abstract and subjective concepts of the division of environmental space. This is illustrated by the diversity of classification schemes that have been applied to conservation planning, including habitat units derived from a mix of data on vegetation types, climate, geology, and topography (Lombard et al. 2003); ecosystem types obtained from satellite imagery (Armenteras et al. 2003); and environmental diversity obtained from a multidimensional environmental space (Faith & Walker 1996). Such approaches, and the identity and number of biodiversity “elements” they generate, are highly dependent on the primary variables used to produce them and the cutoffs applied to distinguish between any two units. Furthermore, the implementation of higher-level biodiversity attributes such as land types and habitats in conservation planning are based on percentage targets. Fixed percentages for each attribute (e.g., 10% of each biome; World Conservation Union [IUCN] 1993) are arbitrary and fail to account for the fact that regions of higher species richness and endemism may require higher representation targets (Rodrigues et al. 2003). Some workers therefore opted for variable percentages, which take into account factors such as rarity, threats, and heterogeneity (e.g., 10–100% of the area of land classes in Lombard et al. 2003), but these still do not solve the problem of, for example, where within a land class a 20% target should be implemented. Further, studies do not support the use of environmental diversity as a surrogate for species diversity (Araújo et al. 2001). Tests of the surrogacy of attributes such as habitat classes are not straightforward to interpret, given that the significance of the results is not assessed to test whether networks selected based on habitat classes are more effective in representing species than what would be expected by chance (e.g., Lombard et al. 2003). They do indicate, however, that significant percentages of species may be missed altogether in reserve networks based on habitat classes and that those most