LETTER Concordance of freshwater and terrestrial biodiversity Robin Abell 1 , Michele Thieme 1 , Taylor H. Ricketts 1 , Nasser Olwero 1 , Rebecca Ng 1 , Paulo Petry 2,3 , Eric Dinerstein 1 , Carmen Revenga 2 , & Jonathan Hoekstra 2 1 World Wildlife Fund, 1250 24th St. NW, Washington, D.C., USA 2 The Nature Conservancy, 4245 North Fairfax Drive, Arlington, VA, USA 3 Museum of Comparative Zoology, Harvard University, 26 Oxford St., Cambridge, MA, USA Keywords Congruence; ecoregions; fish; freshwater; global; priority-setting; rarity-weighted richness; terrestrial. Correspondence Robin Abell, World Wildlife Fund, 1250 24th St. NW, Washington D.C., USA. Tel: +202-495-4507; fax: +202-293-9211. E-mail: robin.abell@wwfus.org Received 14 July 2010 Accepted 6 October 2010 Editor Dirk Roux doi: 10.1111/j.1755-263X.2010.00153.x Abstract Efforts to set global conservation priorities have largely ignored freshwater di- versity, thereby excluding some of the world’s most speciose, threatened, and valuable taxa. Using a new global map of freshwater ecoregions and distri- bution data for about 13,300 fish species, we identify regions of exceptional freshwater biodiversity and assess their overlap with regions of equivalent ter- restrial importance. Overlap is greatest in the tropics and is higher than ex- pected by chance. These high-congruence areas offer opportunities for inte- grated conservation efforts, which could be of particular value when economic conditions force conservation organizations to narrow their focus. Areas of low overlap—missed by current terrestrially based priority schemes—merit inde- pendent freshwater conservation efforts. These results provide new informa- tion to conservation investors setting priorities at global or regional scales and argue for a potential reallocation of future resources to achieve representation of overlooked biomes. Introduction Global priorities for biodiversity conservation are only as robust as the data used to identify them. To date, these priorities have largely neglected freshwater biodiversity due to patchy information on freshwater species (Re- venga & Kura 2003; Brooks et al. 2006). This omission has real implications for conservation investment; for in- stance, the Global Environment Facility’s (GEF) 2005 Resource Allocation Framework, providing guidance on how the GEF spends over U.S. $1 billion each year on environmental projects, incorporates terrestrial biodiver- sity data but none for freshwater (Global Environment Facility 2005). The low profile of freshwater biodiversity in broad-scale priority-setting efforts stands in stark con- trast to its degree of imperilment, with freshwater habi- tats and species worldwide being more threatened than their terrestrial counterparts (Millennium Ecosystem As- sessment 2005; Revenga et al. 2005). This imperilment should raise concern beyond the conservation commu- nity, as human well-being is clearly and directly tied to freshwater systems, and to freshwater species specif- ically, via the ecosystem services they provide (Millen- nium Ecosystem Assessment 2005). Bringing freshwater biodiversity considerations into ongoing debates about conservation priority-setting (Marris 2007) requires a ba- sic understanding of freshwater biodiversity patterns. Given that many conservation priorities are currently driven by terrestrial biodiversity patterns, we asked how regions of exceptional freshwater biodiversity overlap with regions of equivalent terrestrial importance. A new global database of freshwater fish distributions enabled this analysis. Fish are the most speciose vertebrate group, and freshwater fishes comprise approximately one-fourth of all vertebrate species (Dudgeon et al. 2006). Our fresh- water fish database records the presence of about 13,300 species in 426 freshwater ecoregions (Abell et al. 2008), affording the first systematic analysis of global fresh- water fish biodiversity patterns. The analysis allows us to begin to answer the question of whether current Conservation Letters 4 (2011) 127–136 Copyright and Photocopying: c  2010 Wiley Periodicals, Inc. 127