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April 2001: It's a clear winter's day in the Upper Nilgiris and I can see the hills rolling away to the horizon. We are headed for the further reaches of the Mukurthi Wildlife Sanctuary towards the Sispara pass, where the hills plunge down into Silent Valley. This part of the Mukurthi Sanctuary forms the southwest boundary of the Nilgiris, with a ridge to the west, a sheer drop to the New Amarambalam plateau 2,000 m. below. To the south, the hills fall steeply away to the Attapadi plateau. We break at Nadugani at a camping spot by the stream, throw down our backpacks, stretch aching limbs and slake our thirst.
To my surprise, I can spot toads in the stream. It's winter and night temperatures fall to nearly 00C in the open grasslands. The water remains bitingly cold on the sunniest of days, and any sensible amphibian ought to be soaking it up while the going is good, not busy copulating in a freezing stream!
The shola-grassland system is a typical habitat at higher altitudes of the Western Ghats. Above 1,700 m., this system is characterised by rolling grasslands, often dotted with rhododendron and narrow winding riverine tracts, with sholas of various sizes nestling in valleys or spread across hill slopes. The dry season extends between December and April, and these are the driest, hottest months during the day and the coldest during the nights. The southwest monsoon from June to August is soon followed by the northeast monsoon in October and November. In winter, temperatures in the grasslands climb to the 30s during the day and can fall to freezing at night. Ground frost is a fairly common sight on winter mornings.
The sholas, however, are amazing thermostats, and the temperature only varies from 15-200C during the same period. While many animals survive in the relatively homeostatic shola conditions, a few have adapted successfully to the grasslands, particularly cold-blooded animals, such as reptiles and amphibians.
Cold feet
The common toad Bufo melanostictos in the Upper Nilgiris is a source of amazement. It occupies the open grasslands, its preferred habitat, and stays active through the winter, even at night. It even breeds in the cold. I have seen tadpoles in the streams in winter and late one evening, a large female toad with two suitors desperately clinging on to her in Thai Shola. These are the most common amphibians in the grassland; in fact, there are not too many others. Entirely terrestrial and widely distributed throughout India and Sri Lanka, it is large, yellow, brown or black with dark markings, and dry warty skin. The only other toads that I came across in the grasslands were Bufo beddomei and Bufo microtympanum, the latter remarkably similar to the common toad, but distinguished by its small tympanum.
Way up high
The amphibian community of these stunted evergreen forests is far more abundant and speciose, thanks to the habitat's moderate temperatures. Both the mid and high elevation forests of the Western Ghats are dominated by tree frogs, which belong to the genus Rhacophorus, distinguished by their enlarged toe pads. Some species of Rhacophorus have extensive webbing of fore and hind limbs, which gives them an increased surface area for gliding or parachuting. Rhacophorids are old world frogs, widely distributed throughout the Asian tropics and subtropics from India and Sri Lanka to Japan and the Philippines. They are also found in southern Africa. Madagascar has two endemic genera. Most Rhacophorus species build foam nests on vegetation above water, but a few species of the genus Philautus may build foam nests in trees, from where the tadpoles drop into pools of water that collect in tree cavities. Some of these species also have short, non-feeding larval stages.
Interestingly, many species may never descend from the trees during their life cycle, breeding in tiny pools of water that collect in the trunks high up in the canopy. Frogs, in fact, show a far greater diversity of reproductive strategies than is commonly known. There are even a few species in the world that display true viviparity, where the embryos develop in the ovarian duct of the female, after which live young are born.
Rhacophorids are a challenge to both taxonomists and ecologists because their habitat and life history make them amongst the most difficult frogs to study. The identification of species, particularly in genera such as Philautus, has troubled naturalists, herpetologists in the field, and even taxonomists in properly equipped laboratories. A recent amphibian survey in Sri Lanka recorded an increase in the number of species from about 50 to 250, with a large number of new Philautus species being discovered.
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These new discoveries can be partly attributed to the fact that the habitats where these species occur, such as rainforests and high altitude forests, have not been adequately sampled. Secondly, trees, particularly canopies, have rarely been sampled for amphibians. A more fundamental biological or perhaps, philosophical problem lies with the very definition of the concept of ‘species'. Biologists find it hard to agree on what constitutes a species; one person's subspecies or even population is another person's species and vice versa. Despite the debate, it is clear that Rhacophorids constitute a diverse and fascinating group, which has not received sufficient attention in ecological and biological studies. Recent advances in the field of molecular genetics, however, should soon clarify the phylogeny and systematics of this fascinating group.
Based on current information, there are about 60 species of Rhacophorids, of which I have documented about 10-15 species in the Upper Nilgiris. Some species of Philautus are marked by a striking radiating pattern in the eye. We also found one specimen of a bright green frog, probably from the genus Polypedates. It resembled Polypedates pleurostictes but like many of our other specimens, might in fact belong to previously undescribed species. I also came across Micrixalus opisthorhodus in the streams inside the sholas and Rana limnocharis in the ponds and streams of tea estates, particularly in Thai Shola, which, at about 600 ha., is the largest patch in the Nilgiris.
A few good reptiles
There are about 400 species of reptiles in India, and close to 200 in the Western Ghats. About 50 per cent of these reptile species are believed to be endemic. This mountain range, along with the northeast, is thus particularly rich in both reptiles and amphibians.
Reptiles are essentially composed of four groups - lizards, snakes, crocodiles and turtles. There are tuataras as well, but these living fossils are found only in New Zealand. Fortunately for me (just kidding!), there were no crocodiles in the Upper Nilgiris, though their presence in the Moyar river lower in the range is borne out by a sign put up by a wildlife warden with a wry sense of humour: “Bathing, fishing and washing are strictly prohibited. Survivors will be prosecuted." Turtles too are few in number and we came across none.
Dwarf geckos of the Cnamaspis spp., are the most common lizard representatives. I mostly came across these under rocks near streams. They are characterised by round pupils, lack of calls and distinct throat and belly patterns. Most of them are diurnal. The endemic Nilgiri salea is found mostly in the grasslands and displays an amazing variation in colour, from mottled brown to bright green.
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In the two years of my study, I came across less than 10 snakes in all; an olivaceaous keelback Atretium schistosum, a couple of kukris Oligodon taeniolatus and Oligodon venustus and a handful of pit vipers, the most common one in the Nilgiris being the horseshoe pit viper. Pit vipers, generally found at higher altitudes, are less poisonous than the Russel's and saw-scaled vipers. A bite from one of these is likely to cause nothing more than a great deal of unpleasantness to a healthy adult. They have a heat-sensitive loreal pit on their snouts, which is a special adaptation to hunt warm-blooded prey. The grass snake Ahaetulla perroteti is also common in the grasslands.
Of the snakes found at these altitudes, shield-tails or uropeltids are of particular interest as the entire family is endemic to South India and Sri Lanka. There are about 45 species in the Western Ghats, of which an astounding 35 or so are endemic! Most uropeltids live at high elevations in moist and cool areas with daily shade temperatures of 18-220C. These burrowing snakes live in a network of tunnels less than a metre below the surface and feed almost exclusively on invertebrates, mainly earthworms. They are ovoviviparous, giving birth to live young by means of eggs hatched within the body. Their wedge-shaped heads serve as penetration tools with which they extend their tunnels. Their cylindrical bodies end abruptly in short, blunt tails, capped by a single enlarged and rough shield, from which they derive their name - ‘rough-tailed snakes' or ‘shield-tails'. This shield, often ridged or spiny, seems to be involved in the formation of a caudal plug, which is a mass of soil that confuses and deters predators. The smooth colours appear to reduce friction during locomotion in the tunnels. Plectrurus perroteti or the Perrotets shield-tail is the most common shield-tail in the Nilgiris.
Conserving metapopulations
Amphibian and reptilian communities have been documented in the Western Ghats, but few studies have addressed fundamental ecological questions. How many species are, for instance, found in different patches? Is the species richness determined by the size of the patch and its isolation, or by the habitat in the patch?
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Much of the theory surrounding the debate on the species richness of islands and fragmented habitat derives from the paradigm of island biogeography, proposed by Edward Wilson and Robert MacArthur in 1963. This theory suggests that the equilibrium number of species on an island is determined by the extinction of species on the island (which is greater on smaller islands) and the subsequent colonisation of that island by new species (which is greater on islands closer to a source). Nature reserves have also been designed based loosely on the island biogeography theory.
In recent times, island biogeography has been replaced by a broader paradigm known as metapopulation dynamics. This theory deals with habitats like shola-grasslands and other fragmented landscapes, which makes it particularly relevant today, when habitats are being reduced to a fragmented patchwork. This is also relevant in the context of species like amphibians and reptiles whose populations evolve independently on each of these fragments. However, the larger population or group of populations of a species, or ‘metapopulation', is kept alive by the repeated colonisation of empty fragments by movement from occupied fragments. This means that in a network of fragments, some will always be empty, at least as far as some species are concerned. But this does not mean that these fragments constitute unsuitable habitat for the species, they may well be occupied by migrations at a future date, hence the need to protect them. What this suggests is that conventional assessments of biodiversity and habitats may not work with regard to fragmented landscapes, especially with a view to preserving amphibian and reptile fauna.
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The Wildlife Institute of India conducted a study on the fragmentation of rainforests in Kalakad-Mundanthurai and in the Anamalais. Karthikeyan Vasudevan's study on amphibians and N. M. Ishwar's study of reptiles examined the effects of area, isolation and disturbance on herpetofaunal communities. This was achieved by rigorous sampling of rainforests in a large contiguous patch in the Kalakad-Mundanthurai Tiger Reserve and comparison with fragments ranging in size from a few hectares to about 100 ha. in the Anamalais. Such scientific studies enhance our understanding of the ecology and evolution of communities and also offer insights into the conservation of species and the management of ecosystems.
As will be confirmed by most naturalists, habitats in the Upper Nilgiris and other high altitude ecosystems in the Western Ghats have been greatly altered by anthropogenic pressures. In the Upper Nilgiris, much of the original vegetation has been replaced by tea and other plantations. Vast areas of grassland have been planted with eucalyptus, pine and wattle. This habitat alteration could have dire consequences for many animal species as it affects their dispersal and population dynamics. The small 74 sq. km. Mukurthi National Park holds one of the few pristine shola-grassland systems in the Western Ghats, the only remnant of its kind in the Nilgiris (though there are a few large sholas outside the sanctuary at Thai Shola and Avalanche). These sholas offer safe sanctuary to numerous species of Rhacophorids, many of which have not even been documented. As an ecologist I can definitely say to those who determine land use policy in India that until the Nilgiris, and indeed the entire Western Ghats, are protected for their biodiversity and watershed values, we will continue losing species that have never even been described and are found nowhere else on the planet.
by Kartik Shanker, Sanctuary Asia, Vol XXI No. 2, April 2001
