Relative occupancy, endemism, taxonomic distinctiveness and vulnerability: prioritizing regional conservation actions

Abstract

A method is presented whereby regional species are scored and ranked in order of regional conservation importance according to a number of different but complementary 'rarity' criteria. Approaches for determining regional occupancy (RO), relative taxonomic distinctiveness (RTD), relative endemism (RE) and relative vulnerability (RV) rankings for regional faunas are proposed. The continuous variable approach and resultant positively skewed 'rarity' scores suggest easy identification of regional priority species. These methods are collectively applied to a regional mammalian fauna in order to prioritize species for conservation action using a regional priority score (RPS). The proposed method is a comparative relational approach aimed at determining which species require the establishment of viable populations within a regional context. The two species afforded highest RPSs for the Transvaal region, South Africa, are Gunning's golden mole Amblysomus gunningi and Juliana's golden mole A. julianae. These two species are true endemics, with geographic ranges completely restricted to the region. Also of high regional conservation importance are the four-toed elephant shrew Petrodromus tetradactylus, pangolin Manis temminckii and aardvark Orycteropus afer. Although these species have low RE scores, they have high RTD and RV scores. The equal weightings given to the four components of 'rarity' ensures that species achieving a high score in any of these categories will be considered for regional priority listing. This approach is simple, explicit and repeatable, circumventing problems of scale.