The role of scale in designing protected area systems to conserve poorly known species

Bruce E Kendall,Hugh P Possingham,Carissa J Klein

doi:10.1890/es15-00346.1

Abstract

Systematic conservation planning has a substantial theoretical underpinning that allows optimization of tradeoffs between biodiversity conservation and other socioeconomic goals. However, this theory assumes perfect spatial information about the locations of biodiversity features (e.g., species distributions). In practice, planners represent well‐known taxa and other biodiversity “surrogates” in protected area systems, hoping that unmapped species will also be conserved. However, empirical research finds that surrogates predict species presence imperfectly, and sometimes rather poorly, at scales relevant to planning, and existing theory provides no further guidance. We developed new theory, explicitly incorporating aspects of spatial scale, for the representation problem when the locations of species distributions are unknown. Using probability theory and simulated and real species distributions, we found that the probability of adequately representing an unmapped species in a protected area system will be low unless the total fraction of the region being protected is larger than the species representation target. Furthermore, successful conservation depended critically on the relative sizes of the species distribution and of the individual protected areas; fewer, larger protected areas allowed the entire species distribution to fall into an unprotected gap. This scale‐dependence varied with the configuration of the protected area system, with the conservation objective most likely to be attained if the individual protected areas were hyperdispersed (evenly spaced across the planning region). Using these results, we developed three design principles for representing unmapped species in protected areas: (1) The fraction of the region placed in protected areas should be substantially larger than the species‐level representation target; (2) Individual protected areas must be at least one to two orders of magnitude smaller than the unmapped species' distribution; and (3) Protected areas should be evenly dispersed over geographic space. We also performed preliminary investigations of the effects of surrogates and socio‐economic cost data on the probability of adequately representing unmapped species, finding that the primary effect of surrogates may simply be to promote hyperdispersion of protected areas across the planning region, and that seeking to minimize opportunity costs gives poorer conservation results than random protected area placement.

Highlights

Habitat conversion and overharvesting are primary threats to terrestrial and marine biodiversity (Ehrlich 1981, Jackson et al 2001), and are often ameliorated by implementing protected area systems (Soule 1991, Bruner et al 2001, Sodhi et al 2004)
Since r 1⁄4 2c, this is not unexpected. For both random and hyperdispersed protected area configurations, the probability of meeting the conservation objective declined as the species distribution area declined relative to the planning unit area, asymptoting to r (Fig. 3A). This can be understood as the species distribution becoming so small that it can fit into the gap between individual protected areas
Through mathematical and simulation analyses, we have shown that the scale and configuration of protected area systems affects their ability to represent species that were not included as explicit planning targets in the planning process

Summary

Introduction

Habitat conversion and overharvesting are primary threats to terrestrial and marine biodiversity (Ehrlich 1981, Jackson et al 2001), and are often ameliorated by implementing protected area systems (Soule 1991, Bruner et al 2001, Sodhi et al 2004). The typical objective was to maximize the number of species with a target number or fraction of occurrences represented in the protected area system, subject to a budget constraint (or the inverse: minimize the budget required to adequately represent all species; Moilanen et al 2009a) This approach continues to the present day in developing protected are systems for wellstudied taxa such as terrestrial vertebrates (Venter et al 2014). As specified, this is not a spatial problem per se: one needs a list of species presences or abundances within each potential protected area. A combination of large distance between individual protected areas and large overall extent of the planning area is considered valuable to combat spatially contagious threats and disturbances that are not controlled by the protected status, such as hurricanes, oil spills, and the spread of disease (Allison et al 2003, Game et al 2008)

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