The island has the best of everything in terms of underwater topography; now add to this a generous mix of nutrients. Whales need food; lots of it. The two monsoons are in charge of the kitchen, driving a hundred and three river systems (yes, that’s right, 103) bringing down rich organic nutrients from the mountains, slow released from the lichen cloaked cloud forests to the lowlands creating nutrient rich soup around the island. The Blue Whales and the Cloud Forests are inter-connected. Not content with that, whip up some speed with the monsoons and create upwellings, which generate phytoplankton blooms which show up on Indian remote sensing satellites suspended in space in geo-synchronous orbits. All of this food creates fringing coral reefs which are rich in marine species.
Sri Lanka’s coastline which is 432km long has approximately 800 species of marine fish recorded. Sites better publicised for their marine wildlife such as the 1,126km long Gulf of California (Sea of Cortez) has 700 species of fish. The Maldivian islands which stretch across 1,500 km have around 1,200 species recorded and the Great Barrier Reef stretching over 2,600 km has 1,500 species. If we consider the number of marine fish species per unit length, we can see that Sri Lanka has roughly treble the statistic for the Gulf of California and double that for the Maldives. This is a very crude measure but it helps to give a flavour to the layperson of the relative species richness. The nutrient rich water in Sri Lanka and the monsoons which lash the shores reduce visibility in the water.
The lack of good viewing has resulted in its species richness not being understood as almost everyone including dive operators in Sri Lanka think the waters are ‘poor’ for fish compared to other tropical destinations. I have come to realise that ‘poor viewing’ has been confused with ‘poor species richness’, which it is not.
To be clear about context, for big game safaris many countries in Africa are unmatched. Large tropical islands such as Madagascar and New Guinea, lack large land mammal herbivores such as elephants or large carnivores such as leopards (Borneo does not have leopards and the origin of its elephants is disputed) but in absolute terms of species, have huge biodiversity. However, from the viewpoint of commercial wildlife tourism, in terms of ease of access, tourism infrastructure, affordability and with a short time frame of say two weeks, there is no country which has the array of terrestrial big game, endemism-rich species density, spectacular marine wildlife, diverse landscapes and close-knit cultural bonds (love-hate with elephants) with wildlife that is found in Sri Lanka.
The proof of the pudding of the physical, evolutionary and human factors is in the viewing. A visit of mine in April 2012 is an example of good evidence. I had an amazing trip where in the space of two weeks I watched courting Blue Whales, scrumming Sperm Whales, had a mother and baby elephant pad silently past my vehicle and drove back to camp in the gathering dusk, passing leopards out on the hunt.
In this article, I have with some speculation on my part drawn together material that is known from Sri Lanka and the mechanics of large scale processes studied elsewhere. Science is dynamic and what is known and conjectured today can change. But the broad principles should hold true and I hope I have explained why Sri Lanka deserves more attention from both those viewing wildlife for pleasure as well as those studying how planetary forces and time, drive the great engine of evolution and biogeographical distributions. At this point I should add a gentle reminder that in reality evolution is a ‘blind process’ although I have for the purpose of telling a story, written it as if evolution had set out to make a super-rich wildlife destination.
I have to add that although it is arguably the best all-round country for multi-faceted wildlife viewing with ease, it comes with a caveat.
Sri Lanka does need improvement in terms of better interpretation and better facilities for visitors at parks and reserves and more responsible guiding. Finally and alarmingly, less than 8 per cent of its biodiversity rich wet zone remains forested and more attention is needed both locally and internationally to lay emphasis on how special this island is for its wildlife.
Continental Island - Permitted intermittent land connection with mainland allowing immigrant waves. Also continental islands usually inherit a rich stock of species unlike oceanic islands created from volcanic activity.
Origin - Benefits from an ancient stock of species which have become island endemics but shows affinities to groups as far away as in Madagascar.
Two diagonally blowing monsoons and a central mountain range - Highly distinct and extreme climatic zones found more typically on large continental masses.
Isolation - Despite the intermittent land connections and proximity to the mainland, the creation of a climatically distinct wet zone, allowed speciation to operate in the manner it does in isolated environments.
Mountain ranges - The central mountains together with the monsoons have created a topographical and climatic complexity, driving evolutionary forces to create more species. Some mountain ranges have ‘point endemics’ and they create pockets of isolation all over the island.
Deep seas close to shore and shallow seas with mainland. Best of both. - Sri Lanka violates the rule about continental islands having shallow seas around them by having deep seas and submarine canyons (except where it needs shallow seas the most, near the mainland to form intermittent land bridges). The deep seas create conditions for Blue Whales and Sperm Whales to be very close to shore, within sight of naked eye at times.
River Systems - The 103 river systems drain a vast flow of organic nutrients into the deep seas around the island. Per unit length of distance, the coral reefs have more species than more famous marine reserves such as the Gulf of California and the Great Barrier Reef. But rich nutrient load and silt results in poorer visibility than other dive destinations.
Intermittent land bridge connections to mainland - Allowed successive immigrant waves from mainland to boost the number of species in the island and to a lesser extent supply a speciation factory with new material. Later colonisers if successful may evolve into new species if they penetrated ‘pockets of isolation’ in the wet zones. Sri Lanka breaks the rule that moderately sized or small islands don’t have large animals thanks to the intermittent land bridge.
Species Radiations - For example, rainforest tree frogs in the genus Philautus have evolved direct development, skipping egg laying and tadpoles in the water allowing them to radiate into new species. Other groups such as the Shadowdamsels have all 20 plus species endemic to the island. Evolutionary forces have resulted in Sri Lanka breaking the species-area relationship for islands. Land bridges may have played a part, although present evidence is that it has been a small influence.
Ancient Civilisations and Religion - The Elephant Gathering and the high density of Leopards in Yala are both results of intense agricultural farming. A religious respect for other living beings means Blue Whales and Sperm Whales swim up to boats. Birds and other animals are prolific and tame.
Wildlife spectacles, high proportion of endemism, large number of species, large animals and easy viewing Sri Lanka is the best in world for some of the most charismatic or desired species (e.g. Blue Whale – largest animal, Sperm Whale super-pods – largest toothed carnivore) or has special spectacles (e.g. the largest recurring elephant gathering, the Sinharaja Bird Wave, high density of Leopards) all in a compact island with good tourism infrastructure and good specialist guides.
The table summarises a 5 stage process in which a continental island like Sri Lanka would have benefitted by ice ages in enhancing species diversity. This assumes that ice ages acted to lower sea levels in the tropics but did not cover the land with ice sheets as it did in temperate latitudes with islands like Britain. If an island is covered with ice sheets, it will kill species and leave it poor. Britain for example has only 35 species of trees which are native. On the other hand a tropical island like Sri Lanka which was not covered in ice would benefit from a two way exchange of species with the mainland. The dry zone has benefitted from this connection and has species which are found in Southern India and in the northern half of Sri Lanka. The island also has large land mammals such as the elephant and large carnivores such as the leopard not typically found on moderately sized islands.
Puzzlingly and inconveniently, the phylogenetic studies on plants and animals suggest that radiation of species in Sri Lanka took place in the Tertiary age before the series of ice ages in the Pleistocene Epoch (in the Quaternary Period) with the last land bridge connection being as recent as 10,000 years ago. This poses two questions. Firstly, we see that evolutionary events happened in Sri Lanka so many millions of years ago that have left it richer in species compared to much larger tropical islands. New Guinea and Borneo also have varied topographies and have the structural complexity and physical stresses that Sri Lanka has.
If evolutionary events happen because of physical factors combining with random mutations in genes, why has the species per unit area not remained proportionate? Secondly, during the recent ice ages in the Quaternary Period, did the wet zone remain isolated from the Indian mainland surrounded by a sea of dry zone? For answers to the latter question more work will need to be done on the fossil record on plant pollen to understand the extent of different types of forest on the island. The five stage process I have outlined below is a useful general model, but based on what is known at present does not provide the evolutionary answers for Sri Lanka being super-rich in species. This is still a puzzle.