Diversity and the distribution of amphibians in Sri Lanka are directly influenced by the climate, vegetation, topography and geological history of the island. So before looking at the diversity of ampbibians in Sri Lanka we need look at the important enviromental aspects that influence the diversity and distribution of amphibians in the island.
Sri Lanka is a tropical island in the Indian Ocean, located in Southern Asia, southeast of India. It has a total area of 65,610 km², with 64,740 km² of land and 870 km² of inland water. Its coastline is 1,340 km long. The island lies between latitudes 5º 55’ and 9º 51’ N and longitudes 79º 41’ – 81º 54’ E. Its terrain is mostly low, flat to rolling plain, with mountains in the south-central interior. The highest point in the island is Pidurutalagala at 2,524.13 m.
Little bit of Geology
Majority of Sri Lanka's surface lies on Precambrian rock layers, some of it dates back 2 billion years. According to the theory of Plate tectonics these rocks and related rocks forming most of south India were part of a single southern landmass called Gondwanaland. In the beginning of about 200 million years ago, forces within the earth's mantle began to separate the lands of the Southern Hemisphere, and a crustal plate supporting both India and Sri Lanka moved toward the northeast. About 45 million years ago, the Indian plate collided with the Asian landmass, raising the Himalayas in northern India, and continuing to advance slowly to the present time.
Topography Extensive faulting and erosion over time have produced a wide range of topographic features. Three zones (Peneplains) are
distinguishable by elevation. The first peneplain is the largest of the three and extends from sea level to 270m above mean sea level (m.s.l.). The Midlands or the second peneplain extends from 270m to 900m above m.s.l. The Highlands (Third peneplain) extends from 900m to the 2524m a.s.l.
Three major climatic zones based on rainfall are found in Sri Lanka. They are the Dry zone, Wet zone and the Intermediate zone.The dry zone receives an annual rainfall between 1250mm-1900mm and the average temperature ranges between 27-30oC. The dry zone occupies nearly 60% of the island. Approximately 23% of the island is covered by the wet zone and it receives an annual rainfall of 2500–5000 mm per year. The humidity in the wet zone ranges between 75-85%. The intermediate zones consists of intermediate climatic conditions between the dry and wet zones. The annual average precipation of the intermediate zone ranges between 1900-2500mm. The island receives rainfall mainly from the North-eastern and south western monsoons.
VegetationThe above physical factors affect the distribution of vegetation in Sri Lanka. Nine differnt types of forests are known from Sri Lanka. They are Tropical Lowland wet Evergreen Rainforests, Tropical Sub-montane wet Evergreen Rainforests, Tropical Montane Wet Evergreen Rainforests, Tropical Dry Mixed Evergreen forests,Tropical moist Semi-evergreen forests, Tropical Thorn forests, Savannah forests, Grasslands and Mangroves.
Tropical Lowland wet Evergreen Rainforests
Lowland wet evergreen rain forests are distributed in the lowland wetzone upto an elevation of 900m above m.s.l. These forests are dominated by trees of the family Dipterocarpaceae and are found in the south western region of Sri Lanka. Tall trees with an emergant layer and well defined canopy are present in these forests. These forests are home to a high diversity of endemic amphibians of Sri Lanka. Singharaja, Kanneliya- Dediayagla-Nakiyadeniya complex, Kithulgala, Hiniduma, Beraliyakele, Dellawa, Dombagaskanda and Kottawa are well known examples.
Tropical Sub-montane wet Evergreen Rainforests
Sub-montane wet evergreen rainforests are present in the wet zone mid elevations of the central hills. They are dominant in the elevations ranging from 900 - 1500m above m.s.l. Relatively shoter trees with a canopyThe dominant tree species of these forests are Shorea, Syzgium, Calophyllum, Cullenia and Myristica. Sri pada sanctuary, Knuckles and Galaha are few of the forests of this type. This region is also a region with high diversity of endemic amphibians and especially with the genus Philautus.
Tropical Montane Wet Evergreen Rainforests
Tropical montane wet evergreen rainforests are distributed beteween the elevations of 1500-2524m above m.s.l of the central hills in the wet zone of Sri Lanka. These forests are dominated by Calophyllum, Syzgium, Cullenia, Litsea and Myristica species. Upper regions of Sripada Sanctuary and Knuckles, Hortain plains, Hakgala strict nature reserve, Piduruthalagala, and Ramboda are some of the well known forests of this type. This region is has a very high diversity of Philautus species.
Tropical moist Semi-evergreen forests
Tropical moist Semi-evergreen forests are charachteristic to the intermediate zone of Sri Lanka. The dominant plant species in these forests are Filicum, Euphoria, Artocarpus and Myristica species. Forests found in Sigiriya, Monaragala, Randenigala and Kurunegala belongs to this type. Relatively high diversity of amphibians are observed in these forests.
Tropical Dry-mixed Evergreen forests
Tropical dry-mixed evergreen forests are found in the lowland dry zone of Sri Lanka. Majority of the forests in Sri Lanka are of this type. The forests of this region are dominated by species of Manilkara, Chloroxylon, Vitex, Berrya and Schleichera species. Due to the dry conditions in these forests the diversity of amphibians are low and the abundance of the amphibians depends on seasonality.
Tropical Thorn forests
Tropical thorn forests are confined to the semi-arid regions of Sri Lanka. These forests are characterzed with short thorny tree species. A defined canopy and stratification are absent in these forests. The dominant species include Chloroxylon, Salvadora and Randia species. Due to the dry conditions in these areas the diversity of anphibians are very low in these forests.
Savannah forests are observed in the eastern intermediate lowlands of Sri Lanka. These forests are characterized by a continuous cover of grasses with sparsely distributed trees with an open canopy.The dominant trees are fire resisistant species like Terminalia bellarica, Terminalia chebula, Careya arborea, Phyllanthus emblica and Anogeissus latifolius.
There are various types grasslands in Sri Lanka. They are addressed in various names like Pathana, Damana and Thalawa. These graslands are distributed in differnt parts of the island. Pitawala Pathana and Hortain plains are some of the well known Wet Pathana grasslands in Sri Lanka.
Lakes and Marshes
Lakes and marshes are ideal habitats for aquatic amphibians. Most of the lakes and marshes are found in the lowlands of Sri Lanka. The lakes in Sri Lanka are man made but they have provided good habitats for amphibians. Although the diversity of amphibians are low in these habitats the density or the abundance of aquatic amphibian species are high in these habitats.
Mangroves are found along the coastal region of Sri Lanka. Because of the saline conditions of the water in these habitats, it is inhospitable for amphibians. However there are few reports of amphians who are associated in these habitats.