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

Simone Fattorini,François Rigal,Paulo A. V. Borges,Pedro Cardoso,Brock Fenton

doi:10.1371/journal.pone.0033995

Abstract

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.

Highlights

Protected areas are considered one of the most effective and cost-efficient ways to conserve habitats and viable populations of species, representative of the biological diversity of the Earth [1,2]
We used two indices to rank Azorean forest fragments and the entire area of Terceira Island according to arthropod species vulnerability
Species rarity was evaluated according to geographical distribution, habitat specialization and population size of the species

Summary

Introduction

Protected areas are considered one of the most effective and cost-efficient ways to conserve habitats and viable populations of species, representative of the biological diversity of the Earth [1,2]. The identification of biodiversity hotspots and the selection of priority areas are still generally based on the occurrence of target species among vertebrates and vascular plants [20]. This contrasts with the fact that invertebrates, and in particular arthropods, are the most diverse and abundant animal group in virtually all biotopes, performing a number of ecosystem functions that are irreplaceable [21], and include the vast majority of species threatened by extinction [22]. This is due to a number of impediments, namely the scarce or non-existent knowledge about most species [21], including about their distribution (the Wallacean shortfall [23]), changes in space and time (the Prestonian shortfall [21]) and vulnerability to habitat change (the Hutchinsonian shortfall [24])

Methods

Results

Discussion

Conclusion