Subspecies of Sri Lankan Mammals as Units of Biodiversity Conservation, with Special Reference to the Primates

Subspecies embody the evolution of different phenotypes as adaptations to local environmental differences in keeping with the concept of the Evolutionary Significant Unit (ESU). Sri Lankan mammals, being mostly of Indian-Indochinese origins, were honed, in part, by the events following the separation of Sri Lanka from Gondwana in the late Miocene. The emerging new Sri Lankan environment provided a varied topographic, climatic and biotic stage and impetus for new mammalian adaptations. This history is manifest nowhere as clearly as in the diversity of non-endemic and endemic genera, species and subspecies of Sri Lankan mammals that offer a cross-sectional time-slice (window) of evolution in progress: 3 of 53 genera (6%), and 22 of 91 species (24%) are endemic, but incorporating subspecies, the majority 69 of 108 (64%) Sri Lankan land-living indigenous mammal taxa are diversified as endemics. (Numerical details may change with taxonomic updates, but the pattern is clear). These unique forms distinguish Sri Lankan mammals from their continental relatives, and contribute to the otherwise strong biogeographic differences within the biodiversity hotspot shared with the Western Ghats. Regardless of the eventual fates of individual subspecies or ESU’s they are repositories of phenotypic and genetic diversity and crucibles for the evolution of new endemic species and genera. Their importance is highlighted by recent taxonomic studies that have identified more than 20% of infra-specific populations as new endemic species. Such ‘hidden species diversity’ validates not only the policy to conserve the potential for evolutionary processes as manifest by infra-specific diversity, but also, to prioritize the conservation of subspecies over their precise taxonomic definitions. The conservation of biodiversity in practice, therefore, involves firstly the official acknowledgement of the existence and importance of infra-specific diversity, especially in taxa such as primates where it is well expressed; and secondly, the protection of highly threatened natural habitats that constitute the only realistic life-supporting environments for the conservation of Sri Lanka’s diversity in mammals and many other life forms.