Arthropod diversity and the future of all‐taxa inventories

Success or failure in the global challenge of cataloguing all life on Earth will depend to a large extent on our ability to survey and identify the countless millions of arthropod species that remain undescribed. Despite some of the more obvious taxonomic impediments limiting species description rates (Godfray & Knapp, 2004; Wheeler et al., 2004; Evenhuis, 2007; Zhang, 2012), May (2004, 2011) has been vocal in suggesting that the key rate-limiting step in cataloguing biodiversity will ultimately be the craft of collecting specimens in the field. As field ecologists, we naturally have a lot of sympathy with this perspective. In spite of this, the sorts of All-Taxa Biodiversity Inventories (ATBIs) that have been spawned around the world in response to May’s call for more intensive field cataloguing have met with comparatively limited success, and have struggled to maintain adequate funding. The reasons why are really twofold. First, as all field ecologists will know, the volume of arthropod specimens that can be obtained with modern sampling techniques vastly outstrips any capacity to identify this material (Gotelli, 2004); screening large numbers of common species to find the long tail of vanishingly rare species can be prohibitively time-consuming and expensive. Second, the criticism of a ‘stampcollecting’ approach to ATBIs has been hard to shake, and has drawn into question the utility and sustainability of the approach. An alternative approach initiated 10 years ago in Panama has recently ‘come of age’ in the first comprehensive analysis of the spatial distribution of arthropod biodiversity within a lowland tropical forest (Basset et al., 2012). Project IBISCA-Panama (Investigating the BIodiversity of Soil and Canopy Arthropods, Panama module) represents a large-scale research initiative conducted explicitly as a ‘joint venture’ between taxonomists and ecologists. The subtle, but important difference from the ATBI approach is that the research is founded on a set of fundamental ecological questions about the scaling of arthropod species diversity across space and time (Basset et al., 2007), with species discovery and taxonomic inventory as collateral benefits. This is not to imply that taxonomy is in any way a secondary pursuit to ecology, or that it should be considered a service industry to science (Godfray & Knapp, 2004), but rather that the IBISCA approach fosters a dual purpose to the research by formalising a structured inventory within a hypothesis-driven framework. Ecologists clearly benefit from the credibility of taxonomic identification afforded by professional taxonomists and their expertise in compiling life history or distributional information for known species. Taxonomists, too, benefit from participating in a quantitatively structured sampling programme, which can generate new biogeographic or environmental hypotheses about species distributions, and where the relevance of the work to ecological theory and conservation practice is enhanced. We see this as very clearly meeting Gotelli’s (2004) plea for greater collaboration between taxonomy and community ecology, which ultimately strengthens both disciplines.