Use of Arthropod Rarity for Area Prioritisation : Insights from the Azorean Islands

Copyright: ©2012 Fattorini et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.We investigated the conservation concern of Azorean forest fragments and the entire Terceira Island surface using arthropod species vulnerability as defined by the Kattan index, which is based on species rarity. Species rarity was evaluated according to geographical distribution (endemic vs. non endemic species), habitat specialization (distribution across biotopes) and population size (individuals collected in standardized samples). Geographical rarity was considered at ‘global’ scale (species endemic to the Azorean islands) and ‘regional’ scale (single island endemics). Measures of species vulnerability were combined into two indices of conservation concern for each forest fragment: (1) the Biodiversity Conservation Concern index, BCC, which reflects the average rarity score of the species present in a site, and (2) one proposed here and termed Biodiversity Conservation Weight, BCW, which reflects the sum of rarity scores of the same species assemblage. BCW was preferable to prioritise the areas with highest number of vulnerable species, whereas BCC helped the identification of areas with few, but highly threatened species due to a combination of different types of rarity. A novel approach is introduced in which BCC and BCW indices were also adapted to deal with probabilities of occurrence instead of presence/absence data. The new probabilistic indices, termed pBCC and pBCW, were applied to Terceira Island for which we modelled species distributions to reconstruct species occurrence with different degree of probability also in areas from which data were not available. The application of the probabilistic indices revealed that some island sectors occupied by secondary vegetation, and hence not included in the current set of protected areas, may in fact host some rare species. This result suggests that protecting marginal non-natural areas which are however reservoirs of vulnerable species may also be important, especially when areas with well preserved primary habitats are scarce.Data used in this manuscript were obtained in the projects funded by Direcção Regional dos Recursos Florestais (Project: 17.01-080203, 1999–2004) and Direcção Regional da Ciência e Tecnologia (Project: “Consequences of land-use change on Azorean fauna and flora - the 2010 Target, M.2.1.2/I/003/2008). Grants and fellowships to the authors were provided by Fundação Ciência e Tecnologia (SFRH/BPD/40688/2007 and PTDC/BIA-BEC/100182/2008 for PC and FR, respectively) and Azorean Biodiversity Group (CITA-A) (Summer 2010 and Summer 2011 grants to SF)