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

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.

本研究采用基于物种稀有性定义的卡坦指数（Kattan index）所界定的节肢动物物种脆弱性，对亚速尔群岛森林片段以及特塞拉岛全域地表的保护关切程度展开调查。物种稀有性依据地理分布（特有种与非特有种）、栖息地特化程度（在各类生境中的分布范围）以及种群规模（标准化采样中捕获的个体数量）进行评估。其中地理稀有性分为“全球尺度”（仅分布于亚速尔群岛的特有种）与“区域尺度”（仅分布于单个岛屿的特有种）两类。

本研究将物种脆弱性的各项衡量指标整合为两类适用于各森林片段的保护关切指数：其一为生物多样性保护关切指数（Biodiversity Conservation Concern index, BCC），该指数反映某一调查点位中现有物种的稀有性得分平均值；其二为本文提出的生物多样性保护权重指数（Biodiversity Conservation Weight, BCW），该指数反映同一物种类群组成的稀有性得分总和。BCW更适用于筛选脆弱物种数量最多的优先保护区域，而BCC则有助于识别尽管物种数量较少，但因兼具多种稀有性类型而面临高度威胁的区域。

本研究提出一种全新方法，将BCC与BCW指数适配为可基于物种出现概率而非存在-缺失数据开展计算的版本。本研究将新增的概率型指数（命名为pBCC与pBCW）应用于特塞拉岛：通过构建物种分布模型，本研究不仅可还原已有采样区域的物种出现情况，还可推算无数据区域内不同概率等级的物种出现状态。

概率型指数的应用结果显示，部分被次生植被覆盖、因此未纳入当前保护区体系的岛屿区域，实则可能栖息有部分稀有物种。

该研究结果表明，即便仅为边缘性非自然生境，只要其作为脆弱物种的保育库，对其开展保护同样具有重要意义，尤其是在保存完好的原生栖息地较为匮乏的情况下。