Why Sri Lanka is super-rich for wildlife

Meetirigala forest, within an hour from the commercial capital Colombo, is one of a few tiny pockets of species-rich rainforests left in the densely populated Western Province.

Meetirigala forest, within an hour from the commercial capital Colombo, is one of a few tiny pockets of species-rich rainforests left in the densely populated Western Province.

Introduction

This is the story of how evolutionary forces and ancient civilisations have made a tropical island super-rich for wildlife on a scale that is not seen on anywhere on moderately or large islands. Sri Lanka’s super-richness on a proportionate scale eclipses large islands such a Madagascar, Borneo and New Guinea. Alfred Russell Wallace the founder of modern biogeography and Charles Darwin with whom he shared the theory of evolution were both influenced by what they had observed on islands. They both would have been surprised by Sri Lanka. Almost every key driver of evolution seems to have played a part in shaping its biodiversity. The result is an island which is rich in wildlife both in terms of endemic tropical biodiversity as well as large land animals and marine mammals and in concentrations which give rise to some of the world’s most interesting wildlife spectacles. It’s an island which Wallace and Darwin or modern biologists could not have imagined as so many of the biogeographical and evolutionary forces have come in to play simultaneously, to create an unrivalled richness. To top it all, it’s a compact country with good tourism infrastructure making it optimal for wildlife tour operators. This article is about the physical, evolutionary, and human factors that have made Sri Lanka something seemingly imaginary, but yet real.

In a previous article (Sunday Times: Sri Lanka, 13 January 2013) I explained why Sri Lanka has a claim to be the best all-round wildlife destination from a wildlife tour operator’s perspective. In this article I explain the physical, evolutionary and human-induced forces that have made this happen. In essence, I would simplify it conceptually into a three part ‘business model’ for the creation of a top wildlife destination. The first is a set of physical factors, especially those influencing both surface and underwater topography. These together with other planetary phenomena such as plate tectonics and monsoons create structural or topographical complexity on land and under water. Together with time, the topographical or structural complexity on land with monsoonal rainfall has led to the creation of distinct climatic (and hence ecological) zones that are the engine for speciation. Sri Lanka has benefitted from other physical factors such as an ancient Gondwana start and having deep seas close to it unlike other continental islands. Having set up the right conditions for evolutionary factors, the engine of speciation needs to be fed with raw material. The output of the species production factory will be enhanced if besides the operation of long intervals of evolutionary time scales, new species production is boosted by fresh stocks of mainland species through immigrant waves. However, surprisingly, Sri Lanka has managed to produce a phenomenally above normal species richness (explained below with examples) primarily from evolutionary radiations within the island resulting in endemic genera and species. It seems that only later has it supplemented its cargo of species by land-bridging repeatedly with the mainland. This has become more apparent recently through phylogenetic studies using DNA.

Rainforest epiphytes: Epiphytes have overcome the need to grow tall trunks and compete to reach the sunlight by adopting a strategy of leap-frogging to the canopy. Their roots bind onto other trees.

Rainforest epiphytes: Epiphytes have overcome the need to grow tall trunks and compete to reach the sunlight by adopting a strategy of leap-frogging to the canopy. Their roots bind onto other trees.

I would describe the land-bridging as a five stage process for building up the number of species. During periods of glaciations, water is deposited as ice on land and sea levels fall forming a land bridge in the shallow seas. A land bridge is still physically evident in the discontinuous land bridge between Mannar and India, known as Adam’s Bridge. New waves of immigrants are imported to the island via the land bridge and dispersed and then isolated by rising sea levels drowning the land bridge during warming after an ice age (a post glacial). The new arrivals are physically stressed into niches by complex structural and physical factors of topography and climate. In essence the process is connect– import and disperse– isolate–stress–speciate. Glaciations have been a key agent of the island’s richness in allowing large land mammals to colonise and persist in Sri Lanka. However, phylogenetic studies indicate that most of the radiations of endemic species occurred before the land bridge connections of the Pleistocene epoch in the Quarternary Period. So land-bridging has helped, but still unresolved evolutionary forces have been responsible for the species super-richness which occurred before the recent Pleistocene ice age.

The third of the large scale factors is that it has benefitted from human factors or a cultural overlay. The last has two aspects. Firstly, the decline of ancient kingdoms has resulted in great seasonal gatherings of wild elephants and one of the best sites for Leopards. This creates wildlife spectacles which make great viewing on wildlife safaris. (These spectacles have also been complemented by evolutionary factors mentioned above resulting in species radiations which are of great scientific interest even though species such as amphibians are not high on the list of commercial wildlife safaris). The second aspect of the cultural overlay is that the deep respect for life makes wildlife viewing easy as man and animals co-exist with great tolerance.

 Taking Stock: What does Sri Lanka have?

Allow me to start by surprising you. If I asked you which country has the largest seasonally recurring gathering of elephants, what would your answer be? You might think it is somewhere in Africa. And if I asked you for an easy and reliable location to see Blue Whales, the largest animals to have lived on Earth and once one of the hardest animals to see, what would it be? Or consider super-pods of Sperm Whales, the largest toothed carnivore. Is there a country where there is a chance of seeing one on a commercial whale watch? Or one of the best to photograph Leopards or the Sloth Bear (possibly the largest tropical bear)? The surprise is that the answer to all of these is the same country; Sri Lanka. This is both impressive and surprising given that it is in contradiction to conventional island biogeography according to which a moderately sized island (65, 610km2) is unlikely to have large terrestrial animals. Sri Lanka’s potential to be the best for big game safaris outside Africa (albeit on a different and smaller scale) is only now beginning to be discovered by wildlife photographers from both within and outside the island.

All-right, I hear you say; top marks for the big stuff. But what about bio-diversity? Well, let me surprise you again and illustrate it with a recent statistic. First remember that it is well established that the larger the land area, the larger the number of species will be (the species-area relationship). Of course we also need to compare land areas from similar latitudes because species richness increases as one travels from high latitudes to the tropics. Let’s take inland snakes for example. Sri Lanka has 89 species in approximately 66,000km2. How much more would you estimate that other tropical islands which are approximately between nine to twelve times bigger will have? The numbers are surprising: New Guinea (86 species in 786,000km2), Madagascar (91 species in 578,000km2) and Borneo (141 species in 734,000km2). One would have expected these islands to have ten times as many species. But none manage even twice as much and the extent which Sri Lanka is above the species-area curve is conspicuous even if you factor in that more species are to be discovered in the bigger islands. The relative species per unit area is extraordinary and is repeated with many species groups.

Elephant herd - Minneriya, Sri Lanka

Elephant herd – Minneriya: It is hard to imagine that the largest recurring annual concentration of wild elephants occurs in a moderately sized island and not in the continent of Africa. This was unknown until a banker drew attention to this.

So why is Sri Lanka off the curve?

The graph above take the ratios of of species per land area, set the lowest at the level of 1 and then compare the ratios of the other islands against the lowest ration. The result is a relative ranking of species per unit area compared to the lowest in the sample of four islands.

Clearly there is something remarkable and special going on, with the forces of speciation, about which the island has still received little international publicity, although that will change when wildlife film producers pay it more attention. For many vertebrate species, Sri Lanka ranks high in terms of species per unit area. Let’s take a closer look at one vertebrate example where this may not seem to be the case. Costa Rica is synonymous with amphibians. With a land area of 51,000km2 it is fifteen per cent smaller than Sri Lanka and has more amphibian species; 199 versus the 120 from Sri Lanka. So is Sri Lanka not special with amphibians? Although Costa Rica is smaller as a political unit, it benefits from being part of the large physical unit of South America. Therefore in a wider sense the species-area still holds as it has benefitted from being a part of the vast South American continent. A better comparison for Sri Lanka would be a similar sized or larger island which is a natural bio-geographical entity. For example, Madagascar, which is nine times bigger but has only  two and a half times as many amphibian species.

After mammals, birds are the most ‘touristy’ of animals. Sri Lanka has 33 species of endemic birds, largely confined to its lowland and highland wet zones. The number of endemic birds per unit area is high compared to Borneo (52 species) and Madagascar (106 species with a 51% endemism rate), but on par with New Guinea (320 species). A further fifty plus species of birds found in Sri Lanka are shared only with India (subcontinental endemics). Furthermore, it has a special avian spectacle in the Sinharaja Bird Wave. This is the longest continuously studied mixed species bird flock phenomenon in the world, with the largest average number of individuals in a flock from such studies and offers the most stable viewing of usually fast moving tropical bird waves.

The Ceylon Frogmouth: The Ceylon Frogmouth is a subcontinental endemic found in the forests of the Western Ghats in India and in Sri Lanka, suggesting an ancient linkage.

The Ceylon Frogmouth: The Ceylon Frogmouth is
a subcontinental endemic found in the forests of the Western Ghats in India and in Sri Lanka, suggesting an ancient linkage.

The island is the last stop on the Central Asian flyway and a million migrant shorebirds were counted one February in a land based census which suggests that Viddathalthivu in the Mannar region may even be the most important integral site for migrants on the Central Asian flyway. The shorebirds make landfall in Sri Lanka funnelling through the once powerful ancient seaport of Mannar through to the Palatupana Salterns and Bundala National Park in the South: the latter two offer some of the best close viewing of waders in the world.

As explained earlier, a three factor ‘business model’ has been at work to create this extraordinary richness and I will expand on this in the sections below.

 

Creating a super-rich perfect wildlife destination

Imagine your goal was to create the perfect location for wildlife tourism. Sri Lanka would be a good example how to go about it. You want to keep it small so that tourists don’t have to travel too far from one location to another. But not too small as small areas don’t have many animals and also cannot hold on to their animals. An island would be good as isolation allows species to evolve into new species. An ancient start would help. So let’s begin with Sri Lanka being split off from ancient Southern Gondwana, tethered to India and drifting north on the Indian tectonic plate, carrying an ancient cargo of species which results in affinities between species in Madagascar and Sri Lanka. Next, crash the Indian plate into the Asian land mass (creating the Himalayas) and allowing Palaearctic mammals such as the tiger to drift south into India. Anchor Sri Lanka nearby as a continental island to enable immigration of species from the Asian mainland. But leave the island isolated for sufficiently long interglacial periods (where sea levels rise cutting off the island) for the process of speciation to allow endemics to evolve.

The central mountainous core, with two alternating and diagonally blowing monsoons creates structural and climatic conditions which are conducive to speciation processes.

The central mountainous core, with two alternating and diagonally blowing monsoons creates structural and climatic conditions which are conducive to speciation processes.

Isolation and physical stresses have resulted in high levels of endemism (e.g. 100% freshwater crabs, 95% amphibians, 80% land molluscs, 53% freshwater-obligate fish, 52% of dragonflies, 25% flowering plants, etc.). These have been supplemented by the ‘immigrants’ from later land bridge connections. The down-side of repeat connections is that Sri Lanka does not have as high a proportion of endemic species as found on an island such as Madagascar.

Monsoon clouds - The central mountainous core, with two alternating and diagonally blowing monsoons (the South-west and North-east) - © Mohammed Abidally

Monsoon clouds – The central mountainous core, with two alternating and diagonally blowing monsoons (the South-west and North-east) – © Mohammed Abidally

Physical isolation is not enough and ecological isolation is also desirable, both from Asia and within the island. A good trick here is to create a central mountainous core, with two alternating and diagonally blowing monsoons (the South-west and North-east) creating a very moist ‘wet zone’, distinct from a ‘dry zone’. The mountains also allow for a further vertical zonation, allowing more speciation to take place as some species diverge into sister species at different altitudes. Horton Plains National Park, the roof of Sri Lanka ahs many species confined to the highlands.

Build on this theme by up-thrusting a few more rugged, spectacular mountain ranges such as the Knuckles Wilderness creating elevated wet zone ‘islands’ within the wet zone.

Hanuman Langur - Sigiriya: An alpha male Hanuman Langur bares its teeth in a threat display. This could be a relatively recent immigrant as it has not evolved into a district island species.

Hanuman Langur – Sigiriya: An alpha male Hanuman Langur bares its teeth in a threat display. This could be a relatively recent immigrant as it has not evolved into a district island species.

This creates point endemics such as the Tennent’s Leaf-nosed Lizard in the Knuckles. For extra measure add a few mountainous edges to lowland rainforests like Sinharaja to create more point endemics like Karu’s and Erdelen’s Dragon-lizard in Eastern Sinharaja (15 of the 18 agamid or dragon-lizards are endemic). Indulge in more innovation by throwing up a mountain with a wet zone character, Ritigala, surrounded by a  sea of  dry zone with more point endemics and build a legend around it that it was a piece of medicinal herb rich mountain from the Himalayas dropped by the Monkey God Hanuman as told in the Indian epic of Ramayana. Culture and wildlife go hand in hand in this area of ancient kingdoms of Anuradhapura and Polonnaruwa, where the tallest archaeological brick buildings in the whole world; giant stupas, stand. Endemic Toque Monkeys wage ferocious tribal wars watched over by meditating saffron robed monks and are studied in one of the longest running zoological field studies in the world; the Smithsonian Primate Research project.

The Kottawa Forest Reserve is one of many endemic species-rich forests close to the southern city of Galle. This makes Galle the rainforest gateway in Sri Lanka as well as being a good base for whale watching from Mirissa.

The Kottawa Forest Reserve is one of many endemic species-rich forests close to the southern city of Galle. This makes Galle the rainforest gateway in Sri Lanka as well as being a good base for whale watching from Mirissa.

The process of speciation can be accelerated further by throwing in a few evolutionary tricks like direct development in the Rhacophorid Tree Frogs. This allows them to skip the stage of laying eggs in water and having tadpoles developing in water which leaves them vulnerable to periods when ephemeral bodies of water dry out. Instead, allow them to use foam nests in which the eggs develop into little frogs which plop out fully formed allowing one of the significant species radiations discovered in the 20th century to take place. There are many other examples of species radiations; for example all 20 of the Forestdamsels described so far from the island are endemic. In fact Sri Lanka has four, five, and six times as many species of dragonflies per unit area than New Guinea, Borneo and Madagascar respectively. Geological turmoil and variations in the climate creating ‘ecological niches’ could also have created physical stresses that favoured evolutionary variation. In fact, although I have referred to Sri Lanka’s land area as 66,000 km2 , most of the endemism is packed into an area of around 15,000 km2; less than a quarter of the total in what comprises the wet zone. This ‘localisation’ of small-range endemic species makes the endemicity (e.g. 740 endemic flowering plants in the wet zone) and the species richness in the wet zone even more remarkable.

Whilst all this is happening, keep stirring the evolutionary brew with fresh material. A few judiciously spaced out glaciations will lower sea levels forming a land bridge (Adam’s Bridge linking India to Mannar across the Palk Strait) allowing mainland species to immigrate and start anew to evolve into new species. Wildlife tourists like big stuff, so keep the land bridge open to get a good population in of the elephants, Leopards and Sloth Bears. Ooops! Closed it too soon as enough tigers did not make it across to establish a viable population.

Sloth Bear – Yala: Sri Lanka is the best chance for an encounter with a wild Sloth Bear. During the fruiting of the Palu trees around June and July, they are not difficult to see.

Having got the big stuff in, one may as well make an eco-tourism spectacle out of it. This requires some human intervention or anthropogenic factors for the technically minded. Throw in a liberal sprinkling of ancient kings who will usher a golden age of hydraulic civilisation. They will dot the island’s dry zone with grand civil engineering works, with vast lakes (e.g. the Sea of Parakrama) irrigating agriculture. Allow this to go to ruin and perfect conditions are made for the Elephant Gathering at Kaudulla and Minneriya in the North-central Province where over 300 elephants may gather on the receding lakes in search of grazing, water, mates and social networking (elephants don’t use Facebook)! Allow the farmland in the South-east in Yala to turn to grassland where together with the man-made waterholes, conditions are perfect for high densities of Spotted Deer, in turn creating one of the highest densities of Leopards.

The over 2,000 man-made lakes or wewas create wildlife rich wetlands which pre-date the interventionist conservation efforts of the London Wetland Centre. In Yala at Buttuwa Wewa, this results in the largest seasonal concentration in the world of the Mugger or Freshwater Crocodile, the second largest land reptile in the world. Not far away, the soft sandy beaches are visited by five of the seven species of marine turtle including the Leatherback; a giant.

 

Leopard - Yala Sand Lizard - Mannar Black-backed Jackal - Yala

Leopard – Yala Sand Lizard – Mannar Black-backed Jackal – Yala

Introduce Buddhism and Hinduism, two great world religions with a respect for animal life. Most animals lose their fear of people and everything from Leopards in Yala, Blue and Sperm Whales to fighting Purple Swamphens in Talangama Wetland (close to the commercial capital Colombo) are embarrassingly curious and camera friendly for tourists.

Top to bottom: Striped Dolphin (Mirissa), Sperm Whale (Trincomalee), Spinner Dolphins (Kalpitiya) and Blue Whale (Trincomalee). Unusually, Sri Lanka is a continental island with parts of it being close to deep seas and also has deep canyons thrusting in. This makes it the best in the world for Blue Whales and the best chance for a super-pod of Sperm Whales on a commercial whale watch.

Closk-wise from top Left: Striped Dolphin (Mirissa), Sperm Whale (Trincomalee), Spinner Dolphins (Kalpitiya) and Blue Whale (Trincomalee). Unusually, Sri Lanka is a continental island with parts of it being close to deep seas and also has deep canyons thrusting in. This makes it the best in the world for Blue Whales and the best chance for a super-pod of Sperm Whales on a commercial whale watch.

The table on the lef t is not a scientific metric, but gives a non technical reader an easy grasp of the number of species per overall length of an area with marine fish. It shows that Sri Lanka is more relatively rich than most people imagine.

The table on the left is not a scientific metric, but gives a non technical reader an easy grasp of the number of species per overall length of an area with marine fish.
It shows that Sri Lanka is more relatively rich than most people imagine.

With the top side sorted out, the marine side needs some attention as well. The trick here is to have deep water close to shore which suits the large whales (unlike an island like Britain which is covered with shallow seas or the islands of the Indonesian archipelago). Improve on this by having the continental shelf pinching in at the South at Dondra Head near the fishery harbour of Mirissa so that Blue Whales can be seen easily close to shore on a morning whale watch from a coastline studded with luxury villas, boutique hotels and backpacker crash pads. Create a deep 400m depth isobath running north- south for Sperm Whales in Kalpitiya (the Sperm Whale Strip of E 79 35 to E 79 40). Slide a peninsula of golden sandy beaches out onto it so that the Sperm Whales are a mere fifteen minutes by boat. For those for whom boats are not their thing thrust a deep submarine canyon into Trincomalee in the North-east so that Blue and Sperm Whales can be seen from ashore on some days from the temple atop Swami Rock or very rarely from the pool side of beach hotels. For extra good measure throw in a few more canyons on the east coast which are good for enigmatic and elusive beaked whales. All of this is being a bit greedy as the island also has shallow seas where it needs it most; close to the mainland, to allow intermittent land connections for the immigrant waves to supplement the speciation factory. 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 dGdSW1-14own 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 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 1,500km have around 1,200 species recorded and the Great Barrier Reef stretching over 2,600km 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 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.

Sinharaja: The Paradise Combtail - Belontia signata (left) and Werner’s Killifish (right) are part of a treasure trove of 38 species of endemic fish. Over half of the freshwater fish in the island’s streams and rivers are endemic to the island.

Sinharaja: The Paradise Combtail – Belontia signata (left) and Werner’s Killifish (right) are part of a treasure trove of 38 species of endemic fish. Over half of the freshwater fish in the island’s streams and rivers are endemic to the island.

[Left to Right] Leopard - Yala: Yala National Park has one of the highest densities of leopards in the world in part of Block 1. Some leopards are becoming increasingly habituated to vehicles. Marsh Crocodile - Yala: Buttuwa Wewa in Yala is believed to have the highest seasonal concentration of Marsh Crocodiles; the second largest land reptile in the world. Elephant and calf - Minneriya: The Elephant Gathering in Minneriya of fers unrivalled opportunities to observe the social behaviour of this highly intelligent animal.

[Left to Right]Leopard – Yala: Yala National Park has one of the highest densities of leopards in the world in part of Block 1. Some leopards are becoming increasingly habituated to vehicles.
Marsh Crocodile – Yala: Buttuwa Wewa in Yala is believed to have the highest seasonal concentration of Marsh Crocodiles; the second largest land reptile in the world.
Elephant and calf – Minneriya: The Elephant Gathering in Minneriya of fers unrivalled opportunities to observe the social behaviour of this
highly intelligent animal.

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.

Left Sri Lanka Keelback Water Snake, Middle Reticulated Shrub-frog and Right Green Pit Viper. Sri Lanka is disproportionately rich in reptile species.

Left Sri Lanka Keelback Water Snake, Middle Reticulated Shrub-frog and Right Green Pit Viper. Sri Lanka is disproportionately rich in reptile species.

Kangaroo Lizard (endemic). 15 of the 18 Agamid or Dragon Lizards in the island are endemic; an example of a species radiation.

Kangaroo Lizard (endemic). 15 of the 18 Agamid or Dragon Lizards in the island are endemic; an example of a species radiation.

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% 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.

Left Green’s Jewel. All three Jewels found in Sri Lanka are endemic. Middle and Right Brinck’s Forestdamsel and Blurry Forestdamsel. A remarkable species radiation is that of the Forestdamsels where all 20 described so far are endemic.

Left Green’s Jewel. All three Jewels found in Sri Lanka are endemic. Middle and Right Brinck’s Forestdamsel and Blurry Forestdamsel. A remarkable species radiation is that of the Forestdamsels where all 20 described so far are endemic.

  A summary of the 3-factor super-rich model

20-A-Summary-of-3-factor

Ice Ages and Speciation

Toque Monkey - Dambulla: The endemic Toque Monkey has been the subject of one of the longest continuously running zoological field studies in the world. It has three distinct races on the island. The distinct climatic zones in this moderately-sized island have resulted in some animals having sub-species (or geographical races) in the dr y, wet and montane zones. River systems and climatic zones create further ‘islands of habitat’ within the island.

Toque Monkey – Dambulla: The endemic Toque Monkey has been the subject of one of the longest continuously running zoological field studies in the world. It has three distinct races on the island. The distinct climatic zones in this moderately-sized island have resulted in some animals having sub-species
(or geographical races) in the dr y, wet and montane zones. River systems and climatic zones create further ‘islands of habitat’ within the island.

The table below 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.

GdSW1-25If 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.

Data Tables

The tables below take the ratios of species per land area and set the lowest at a level of 1. They then compare the ratios of the other islands against this score of 1. The result is a relative ranking of species per unit area compared to the lowest in the sample of four islands. New species continue to be described in all of the four islands and the numbers will continue to change.

However, unless some dramatic discoveries are made elsewhere, it’s unlikely that Sri Lanka’s relative super- richness will be diminished.

GdSW1-26 GdSW1-27 GdSW1-28 GdSW1-29 GdSW1-30 GdSW1-31 GdSW1-32

Here there be giants…

GdSW1-33

It is a surprise that a moderately-sized continental island like Sri Lanka is the best place in the world to see the largest animal that has lived on the planet, the Blue Whale, as well as to be where the largest annually recurring concentration of wild elephants is found.

The Blue Whale was one of the hardest animals to see until when in May 2008 it was publicized that Sri Lanka was the Best for Blue. The Asian Elephant (smaller than the African Elephant) is the second largest land mammal. Outside the continent of Africa, the best elephant encounters are not on the mainland of another continent but on the island of Sri Lanka.

GdSW1-34

Story | Gehan de Silva Wijeyeratne.
Photographs | Gehan de Silva Wijeyeratne (except for monsoon cloud image credited to Mohammed Abidally).
Graphics | Navin Balasuriya (The Sunday Times) and Rukshan Rajapakse (TBWA/TAL).
Pdf design | Keith Wijesuriya

Gehan de Silva Wijeyeratne has played a pivotal role in branding Sri Lanka for its wildlife using a blend of writing, photography, business acumen, media skills and science.  Among many books he has written and photographed include Wild Sri Lanka (John Beaufoy Publishing), Sri Lankan Wildlife (Bradt Travel Guides) and two photographic guides to the Mammals and Birds of Sri Lanka respectively with New Holland Publishers. He can be found on Facebook, LinkedIn and Flickr.

The article above by Gehan de Silva Wijeyeratne was originally published as a two part article in the Sunday Times and subsequently laid out as a pdf by Keith Wijesuriya with addittional text and graphics. The original graphics are by Nalin Balasuriya of the Sunday Times. The complete story pdf with the full list of acknowledgements is attached below.

Download the original article which ran as a two part series in The Sunday Times: Sri Lanka Super Rich Wildlife (2013 07 LR)

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