Indicators of the Status of and Trends in Global Biological, Linguistic and Biocultural Diversity

Biodiversity is in global decline and around 19% of the world's vertebrate species are listed as threatened on the IUCN Red List (Baillie et al. 2010; IUCN 2013). Linguistic diversity is also in decline and it is believed that as many as 90% of the world's 7,000 languages are threatened with extinction this century (Krauss 1992; Nettle and Romaine 2000). It has also been noted that there is a strong similarity in the distributions of terrestrial species diversity and linguistic diversity at the global scale, with the greatest richness found in the humid tropics and the lowest richness in the cold temperate zones (Mace and Pagel 1995; Sutherland 2003; Gavin et al. 2013). The term biocultural diversity has come into use to describe the collective diversity of species, languages and cultures around the world and their ongoing declines (Maffi 2001b; Harmon 2002). One of the papers presented here develops the first national index of biocultural diversity, which confirms the pattern of greatest richness in the tropics, particularly in Southeast Asia (Loh and Harmon 2005).

However, measures of the state of biological, linguistic and biocultural diversity based on richness alone simply record the number of species or languages present and ignore underlying trends in abundance or populations of species or speakers of languages. Extinction risk has been the most widely-used measure of the status of both species and languages, but indicators based on time-series population data offer an alternative and more responsive measure of status and trends. The other papers presented here describe the development of Living Planet Index (Loh et al. 2005; Collen et al. 2009), an indicator which aggregates trends in populations of several thousand vertebrate species worldwide and shows an overall decline of about 30% over four decades since 1970, and the Index of Linguistic Diversity (Harmon and Loh 2010; Loh and Harmon 2014), a closely-related indicator based on trends in speaker numbers of around a thousand languages worldwide, and which also shows a decline of about 30% over the same period. At the regional level, the respective trends diverge. For biodiversity, there was a greater rate of decline in the tropics compared with temperate regions, whereas for linguistic diversity, there was a far higher rate of decline in the Americas, Australia and the Pacific compared with Africa, Asia and Europe. An analysis of the threat status of 1,500 languages using the IUCN Red List criteria reveals that 27% languages are threatened with extinction and confirms the regional pattern in the status of languages apparent in the Index of Linguistic Diversity. The differing regional patterns between the declines in languages and species reflect differences in the proximate drivers of diversity loss, where habitat loss or degradation are the major causes of species population declines (Millennium Ecosystem Assessment 2005), while linguistic diversity is lost primarily through language shift, a process whereby a politically, socially or economically dominant language displaces local or indigenous languages either as a result of colonialization, industrialization or migration (Nettle 1999).