Review

# Global Biodiversity Conservation Priorities

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Science  07 Jul 2006:
Vol. 313, Issue 5783, pp. 58-61
DOI: 10.1126/science.1127609

## Abstract

The location of and threats to biodiversity are distributed unevenly, so prioritization is essential to minimize biodiversity loss. To address this need, biodiversity conservation organizations have proposed nine templates of global priorities over the past decade. Here, we review the concepts, methods, results, impacts, and challenges of these prioritizations of conservation practice within the theoretical irreplaceability/vulnerability framework of systematic conservation planning. Most of the templates prioritize highly irreplaceable regions; some are reactive (prioritizing high vulnerability), and others are proactive (prioritizing low vulnerability). We hope this synthesis improves understanding of these prioritization approaches and that it results in more efficient allocation of geographically flexible conservation funding.

## Challenges Facing Global Prioritization

Limitations of data have thus far generally restricted global conservation prioritization to specialist estimates of irreplaceability, to habitat loss as a measure of vulnerability, and to coarse geographic units defined a priori. Over the past 5 years, spatial data sets have been compiled with the potential to reduce these constraints, particularly for mammals, birds, and amphibians (5). When these maps are combined with assessment of conservation status, they enable the development of threat metrics directly based on threatened species (36). So far, the main advances to global prioritization enabled by these new data are validation tests of existing templates (31). Encouragingly, global gap analysis of priorities for the representation of terrestrial vertebrate species in protected areas (36) and initial regional assessment of plants (37) yield results similar to existing approaches (fig. S2).

Invertebrates represent the bulk of eukaryotic diversity on Earth with more than a million known species and many more yet to be described (5). The conservation status of only ∼3500 arthropods has been assessed (5), so global conservation priority is far from being able to incorporate megadiverse invertebrate taxa (8, 23). Although some regional data shows little overlap between priority areas for arthropods and those for plant and terrestrial vertebrate taxa (38), preliminary global data for groups such as tiger beetles and termites suggest much higher levels of congruence (39). Similarly, pioneering techniques to model overall irreplaceability by combining point data for mega-diverse taxa with environmental data sets produce results commensurate with existing conservation priorities (40). These findings, although encouraging, in no way preclude the need to use primary invertebrate data in global conservation prioritization as they become available.

Aquatic systems feature poorly in existing conservation templates. Only one conservation prioritization explicitly incorporates aquatic systems (16). The most comprehensive study yet, albeit restricted to tropical coral reef ecosystems, identified 10 priority regions based on endemism and threat (41). Eight of these regions lie adjacent to priority regions highlighted in Fig. 3, raising the possibility of correspondence between marine and terrestrial priorities, despite the expectation that surrogacy of conservation priorities will be low between different environments (42). Efforts to identify freshwater priorities lag further behind, although initial studies reveal a highly uneven distribution of freshwater fish endemism (39).

Most measurement of irreplaceability is species based, raising the concern that phylogenetic diversity may slip through the net of global conservation priorities (8, 23, 43). However, analyses for mammals (44) find that priority regions represent higher taxa and phylogenetic diversity better than would be predicted by the degree to which they represent species. Islands such as Madagascar and the Caribbean hold especially high concentrations of endemic genera and families (39). A heterodox perspective argues that the terminal tips of phylogenetic trees should be higher priorities than deep lineages (45). In any case, the balance of work implies that even if phylogenetic diversity is not explicitly targeted for conservation, global prioritization based on species provides a solid surrogate for evolutionary history.

That global conservation priority regions capture phylogenetic history does not necessarily mean that they represent evolutionary process (8). For example, transition zones or “biogeographic crossroads,” frequently overlooked by conservation prioritization, could be of particular importance in driving speciation (46). On the other hand, there is evidence that areas of greatest importance in generating biodiversity are those of long-term climatic stability, especially where they occur in tropical mountains (47), which are incorporated in most approaches to global conservation prioritization. The development of metrics for the maintenance of evolutionary process is in its infancy and represents an emerging research front.

A final dimension that will prove important to assess in the context of global conservation prioritization concerns ecosystem services (43). Although the processes threatening biodiversity and ecosystem services are likely similar, the relationship between biodiversity per se and ecosystem services remains unresolved (48). Thus, while it is important to establish distinct goals for these conservation objectives (49), identification of synergies between them is strategically vital. This research avenue has barely been explored, and questions of how global biodiversity conservation priorities overlap with priority regions for carbon sequestration, climate stabilization, maintenance of water quality, minimization of outbreaks of pests and diseases, and fisheries, for example, remain unanswered. However, the correspondence between conservation priorities and human populations (25, 26) and poverty (4, 5) is an indication that the conservation of areas of high biodiversity priority will deliver high local ecosystem service benefits.

## From Global to Local Priorities

The establishment of global conservation priorities has been extremely influential in directing resources toward broad regions. However, a number of authors have pointed out that global conservation prioritization has had little success in informing actual conservation implementation (8, 23). Separate processes are necessary to identify actual conservation targets and priorities at much finer scales, because even within a region as uniformly important as, for example, Madagascar, biodiversity and threats are not evenly distributed. Bottom-up processes of identification of priorities are therefore essential to ensure the implementation of area-based conservation (50).

Indeed, numerous efforts are underway to identify targets for conservation implementation. Many focus on the site scale, drawing on two decades of work across nearly 170 countries in the designation of important bird areas (51). There is an obvious need to expand such work to incorporate other taxa (52) and to prioritize the most threatened and irreplaceable sites (33). Such initiatives have recently gained strong political support under the Convention on Biological Diversity, through the development of the Global Strategy for Plant Conservation and the Programme of Work on Protected Areas. Both mechanisms call for the identification, recognition, and safeguarding of sites of biodiversity conservation importance. Meanwhile, considerable attention is also targeted at the scale of landscapes and seascapes to ensure not just the representation of biodiversity but also of the connectivity, spatial structure, and processes that allow its persistence (53).

Global conservation planning is key for strategic allocation of flexible resources. Despite divergence in methods between the different schemes, an overall picture is emerging in which a few regions, particularly in the tropics and in Mediterranean-type environments, are consistently emphasized as priorities for biodiversity conservation. It is crucial that the global donor community channel sufficient resources to these regions, at the very minimum. This focus will continue to improve if the rigor and breadth of biodiversity and threat data continue to be consolidated, which is especially important given the increased accountability demanded from global donors. However, it is through the conservation of actual sites that biodiversity will ultimately be preserved or lost, and thus drawing the lessons of global conservation prioritization down to a much finer scale is now the primary concern for conservation planning.

Supporting Online Material

Figs. S1 and S2

Table S1

References and Notes