Abstract
All mammals originated on the supercontinent of Pangaea in the Mesozoic era during the “Age of Reptiles.” However, the crown ancestors of contemporary mammals did not flourish until major environmental and biotic changes had occurred. An asteroid collided with earth at the end of the Cretaceous Period (the K-Pg boundary event) wiping out non-flying dinosaurs and primitive mammals. It was followed by large-scale volcanism, a spike in atmospheric oxygen and the proliferation of flowering plants. New niches became available for the ancestors of today’s mammals to fill. Evidence suggesting whether the ancestors of the Sri Lankan and Indian mammals originated on the tectonically marooned Indian plate before crashing into Asia or on the Laurasian supercontinent is inconclusive. Modern Sri Lankan mammals show their greatest affinity with those of southern India, and were more diverse in the Pleistocene when rhinoceros, hippopotamus, wild dogs, gaur and lions enriched the island’s landscapes. Native Sri Lankan land-based mammals are diversified into about 108 unique taxa (among 91 species and 53 genera), differentiated as phenotypic adaptations to sharply contrasting environments among seven major phyto-climatic zones. Endemic subspecies are distributed fairly equally across different phyto-climatic zones (n=24 to 29), except in the highlands where they are fewer (n=14) having evolved rapidly to species and genera among the insectivores and rodents whose reproductive rates are high. Conversely, greater numbers of endemic species (n=13) and genera (n=3) occur in the highlands than in the other zones (2-6 endemic species, no endemic genera). The prevalence of endemism is inversely related to body size or vagility. This suggests a greater probability of genetic exchange among distant populations of large bodied mobile mammals within Sri Lanka, as well as with Indian fauna during periods of land bridges in the Pleistocene. Most (8 of 13) endangered and critically endangered endemic mammals occur in the wet montane regions that offer the least Protected Areas (PAs). More than 85% of PAs occur in the extensive dry zone about half of which is not suited for water dependent mammals whose distributions are restricted to alluvial forests (less than 1% of PAs). Historically, the national cost of conservation has been low and therefore politically palatable. Current conservation urgently requires a major change in management policy combined with realistic investment to prevent extinctions of many endemic mammals and other unique Sri Lankan biota.
Highlights
Chance events in the geological history of the earth have placed Sri Lanka in a globally unique position with respect to biodiversity
Given that mammalian phenotypes vary geographically within a species, and some of these population variants are distinct and unique to Sri Lanka, or endemic, it raises the question on which taxonomic level should we focus for scientific consideration and conservation management? From the point of view of unravelling evolutionary trajectories as well as conservation, the focus should be on the adaptive diversity across the range of a taxon, which reflects its evolutionary success (Moritz, 2002; Hey et al, 2003)
Many water dependent mammals are confined to the very restricted areas of permanent water that constitute less than 1% of these forest or in the protected areas located there
Summary
Chance events in the geological history of the earth have placed Sri Lanka in a globally unique position with respect to biodiversity. Apical flora and fauna reside in Sri Lanka, especially in the highlands. They are the products of at least 200 million year biological evolution and adaptation to the shifting of continental plates, massive volcanic eruptions and periods of glaciation. This extraordinary gift of nature to Sri Lanka is not widely appreciated and is under threat of permanent loss. The aims of this report are: firstly, to reiterate the importance of focusing not merely on the species, but especially on the subspecies of Sri Lankan mammals for conserving their diversity (Dittus, 2013); secondly, to relate the taxonomic differentiation of mammals to their biogeography, through geological time (Figure 1) and to the various contemporary phyto-climatic environments of Sri Lanka; and to reflect on the status and challenges of conserving mammalian biodiversity in relation to ecology and supporting habitats
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