How to Quantify Endemism

Abstract

While the definition of endemism is clear, there are multiple ways of measuring endemism, and each has its own inherent biases. We discuss the most frequently used and recently developed measures. Ultimately all these measures are relative (i to iii), and care must be taken when making comparisons. Further, issues such as the species concept (i), the dependency on regional species-richness or the distribution of range sizes in the whole species pool (ii), and special problems in statistics, e.g. spatial autocorrelation (cf. Bruchmann. Plant endemism in Europe: spatial distribution and habitat affinities of endemic vascular plants. Dissertation, University of Flensburg, Flensburg. URL: www.zhb-flensburg.de/dissert/bruchmann, 2011; Kühn, Divers Distrib 13:66–69, 2007), need to be accounted for, since they can introduce bias. Measures of endemism can also be scaled in ways that emphasize conservation priorities: for example, in all metrics, endemics can be weighted according to their range size, age, evolutionary distinctiveness or level of threat (cf. Kraft et al., Divers Distrib 16:403–413, 2010; Cadotte and Davis, Divers Distrib 16, 376–385, 2010). The resulting indicators allow scientists to combine biogeographical data with ethical values, based on the assumption that species are not all of equal value to conservation programs (iii). Different methodologies result in different kinds of values and information and may designate different regions as centers of endemism (Carine et al., J Biogeogr 36:593–611, 2009), making it difficult to focus conservation efforts. However, Huang et al. (J Syst Evol 49/2:81–94; Divers Distrib:1–16, 2011, 2012) have shown that five diversity indices describing endemism in China are significantly correlated with each other, suggesting that broad agreement between indices is possible.