DIVERSITY & ENDEMISM
There are a minimum of 6,000 vascular plant species in the Western Ghats and Sri Lanka hotspot, of which more than 3,000 (52 percent) are endemic. There are also more than 80 endemic plant genera, many of which have only one species.
The Western Ghats harbors approximately 5,000 species of vascular plants belonging to nearly 2,200 genera; about 1,700 species (34 percent) are endemic. There are also 58 endemic plant genera, and, while some are remarkably speciose (like Niligrianthus, which has 20 species), nearly three-quarters of the endemic genera have only a single species.
Some prominent genera and families are represented by large numbers of endemic species, such as Impatiens with 76 of 86 species endemic, Dipterocarpus with 12 of 13 species endemic, and Calamus with 23 of 25 species endemic. Of the 490 tree species recorded from low- and mid-elevation forests, 308 species are endemic. The only gymnosperm tree, Podocarpus (=Nageia) wallichianus, is also endemic. Of the 267 species of orchids, 130 are endemic.
Similarly, plant diversity and endemism in Sri Lanka are quite high, with 3,210 flowering plant species in 1,052 genera, of which 916 species and 18 genera are endemic. Amazingly, all but one of the island’s more than 55 dipterocarp species are found nowhere else in the world. In addition, the island’s ferns (although not recently assessed) are estimated to number about 350 species. Approximately 433 plant species, and at least five genera, are confined to Sri Lanka and the Western Ghats combined.
In the Western Ghats, the Agasthyamalai Hills in the extreme south are believed to harbor the highest levels of plant diversity and endemism at the species level. Nearly 87 percent of the region's flowering plants are found south of the Palghat Gap (37 percent being exclusive to this sub-region); these figures decrease to about 60 percent and 5 percent, respectively, in the Nilgiri Hills. In Sri Lanka, diversity, richness, and endemism across all taxa are much higher in the wet (including the montane) zone than in the dry zone. Indeed, the wet zone, which accounts for only a quarter of Sri Lanka’s territory, contains 88 percent of the flowering plants occurring in the island, and 95 percent of its angiosperm endemics.
The avifauna of the Western Ghats and Sri Lanka is diverse, but endemism is not exceptional. There are more than 450 known bird species from the hotspot, of which about 35 are endemic. More than 20 species are endemic to Sri Lanka, mostly from the lowland rainforests and montane forests of the island's southwestern region. Both the Western Ghats and the island of Sri Lanka are considered as Endemic Bird Areas by BirdLife International.
Of the endemic species, 10 are considered threatened, including the green-billed coucal (Centropus chlororhynchos, VU), the Sri Lanka whistling thrush (Myiophonus blighi, EN) and rufous-breasted laughingthrush (Garrulax cachinnans, EN). The hotspot also holds several widespread threatened waterbird species, including the spot-billed pelican (Pelecanus philippensis, VU) and the lesser adjutant (Leptoptilos javanicus, VU). Another threatened species, the Kashmir flycatcher (Ficedula subrubra, VU), breeds in the Himalayas and winters in the Western Ghats and in Sri Lanka.
The hotspot is home to about 140 mammal species, although less than 20 are endemic. While mammal diversity is lower here than in some other tropical hotspots, the hotspot does support a significant diversity of bats, with nearly 50 species and one endemic genus, represented by the bat Latidens salimalii (CR), which is endemic to the High Wavy Mountains in the Western Ghats. In addition, there are three genera confined to Sri Lanka, each represented by single species: Pearson’s long-clawed shrew (Solisorex pearsoni, EN), Kelaart's long-clawed shrew (Feroculus feroculus, EN), and the Ohiya rat (Srilankamys ohiensis).
Among flagship mammal species, the most prominent are the lion-tailed macaque (Macaca silenus, EN), found in highly fragmented tropical rain forests in the Western Ghats, and the endemic Nilgiri tahr (Hemitragus hylocrius, EN), which lives in the montane grasslands of the Western Ghats. One of the most threatened Indian mammals, the Malabar civet (Viverra civettina, CR), is known only from the Malabar Plains, which are densely populated and the focus of most development activities.
The hotspot also has important populations of the Asian elephant (Elephas maximus, EN). The Western Ghats is home to about 11,000 animals, while in Sri Lanka the species has been nearly extirpated from the wet zone and only about 2,500 survive elsewhere on the island.
The highest levels of vertebrate endemism in the Western Ghats and Sri Lanka hotspot are among reptiles and amphibians. Of the region's more than 260 reptile species, about 175 (66 percent) are endemic. One quarter of the nearly 90 reptile genera in the hotspot are endemic, and nine of these are represented by single species. Families such as Uropeltidae (47 of 48 species), Gekkonidae (18 of 30), and Agamidae (20 of 26) exhibit very high endemism.
Endemism is particularly marked among amphibians in this hotspot: of approximately 175 species, roughly 130 are endemic. In the case of Sri Lanka, amphibian diversity is only now becoming better known, and the country's wet zone alone may contain as many as 140 endemic species. Across the hotspot, the genus Philautus is particularly well represented with over 50 species occurring, and nearly all of them are endemic.
Additionally, six genera (out of a total of 28) are endemic to the Western Ghats and Sri Lanka. Recently, a new amphibian family was discovered in Kerala in the Western Ghats; the burrowing anuran family, Nasikabatrachidae, with the single species Nasikabatrachus sahyadrensis (EN), represents the only endemic amphibian family in the hotspot. The closest living relatives of this family are the Sooglosside in the Seychelles.
Unfortunately, the amphibian fauna fare particularly high levels of threat, driven particularly by the continuing levels of habitat loss. Among the endemics, over 85 species are considered threatened. Amphibian extinctions are also relatively well documented, with some 20 historically recorded extinctions.
Many freshwater fish occupy very limited ranges in the Western Ghats and in Sri Lanka. Nearly 140 of more than 190 species of strictly freshwater fishes are endemic to the hotspot. There are also nine endemic genera, including one, Malpulutta, found only on Sri Lanka. In the Western Ghats, the southern region is known to be more diverse than the central and northern regions.
Although knowledge of invertebrate diversity in the Western Ghats and Sri Lanka is poor, the hotspot is believed to have significant levels of endemism within certain groups. For example, more than 100 of nearly 140 tiger beetle species are endemic. However, this may not hold true across groups: the number of butterfly species in this region is relatively low, with only 37 endemics of 330 in the Western Ghats, and 24 of 234 species endemic to Sri Lanka.
Sri Lanka has a number of unique endemics, including Aneuretus simoni, the only surviving representative of one of the world’s 14 ant subfamilies. It also hosts more than 50 known species of endemic freshwater crabs (all in the Parathelphusidae family), all of them endemic. These species are gravely threatened by habitat fragmentation and degradation, as well as by pesticide use in nearby areas. A preliminary assessment of their conservation status indicates that they are in dire straits: of the 51 species, 23 are listed as Critically Endangered, seven as Endangered, and another seven as Vulnerable.