Conservation and biogeography of threatened Amphibians of Eastern Sinharaja

by Madhava Meegaskumbura on January 27th, 2012

This work was presented at a Theme Seminar at SLAAS 2011,  and later published in FROGLOG 100. This is a slightly shorter version of that.
Despite some recent remarkable discoveries of new species, Sri Lanka has already lost 21 species of Amphibians, this is about half the confirmed extinctions in the world. Nineteen of these Sri Lankan forms belong to genus Pseudophilautus, all of which are terrestrial direct developers and many of which are habitat specialists, often requiring the shade of a canopy covered forest for survival. Eighty six percent of the currently known 67 Pseudophilautus species described from Sri Lanka are threatened with extinction (CR, EN or VU, IUCN Redlist Categories) or are extinct (EX). Eastern Sinharaja (ES) harbors 10 Pseudophilautus species of which 5 are Critically Endangered (Ps. procax, Ps. papillosus, Ps. lunatus, Ps. simba and Ps. limbus), 4 are Endangered (Ps. poppiae, Ps. ocularis, Ps. auratus and Ps. decoris) and 1 is Data Deficient (Ps. regius); seven of the ten species are endemic to ES, highlighting the importance of ES as a refugium for threatened frogs. Many of the Pseudophilautus, including the seven ES forms are point endemics (very restricted distributions). The point endemic nature of Pseudophilautus is due to a combination of the following characteristics: terrestrial direct development, habitat specialization, requirements of unique climatic conditions and constraints to reproduction.
Through ex-situ and in-situ observational studies and molecular phylogenetic analyses it is confirmed that all Pseudophilautus species show direct development. These frogs also show two major reproductive behaviors: soil nesting (most species) and arboreal nesting (only seen in three species); both these behaviors are observed in ES Pseudophilautus species.
Seven of the ES species, especially the Critically Endangered forms are only found in canopy-covered forests. Three of the ten species are found both in canopy covered forest and grasslands. The forest species specialize further by selecting certain perching heights and microhabitats (distance from water) within the forest strata. Species that survive in grassland take refuge amongst litter and grass tufts.
Recent microclimate monitoring work by us for temperature, relative humidity, light intensity and UV-radiation daytime fluctuations are dramatically different for forest habitats (includes natural and regenerating forests) and degraded grasslands and roads. However, the nighttime, fluctuations were more or less similar in all habitats. Some of the forest species, do not hide but lay on leaf surfaces, exposed to the subdued light and UV rays (in small amounts, UV is important for frog metabolism) that filters through the canopy, this they will never be able to do in an open habitat due to extreme conditions. So it seems that daytime climatic conditions, that are regulated by the particular habitat types is important in species distribution, rather than the night time conditions. When restoration of habitats is attempted, aiming to conserve amphibians, the conditions needed during the daytime should be closely considered.
When the distribution of Eastern Sinharaja Pseudophilautus are traced on a molecular phylogenetic tree (that of Meegaskumbura and Manamendra-Arachchi, 2011) it is apparent that they are distinct evolutionary lineages representative of the major clades of Pseudophilautus in Sri Lanka. The basal nature of several of the clades and the high endemicity suggest that ES is a montane refugium and a center of endemism. Moreover, sister species of some of the Eastern Sinharaja Pseudophilautus are found in Lower Sinharaja (Kudawa) region (eg. P. decoris and P. mittermeieri, P. procax and P. abundus, P. papillosus and P. reticulatus sister species pairs). This shows the importance of maintaining the quality of habitat of Eastern Sinharaja and also the connectivity between Eastern and lower Sinharaja.
Several species that were not discovered in extensive surveys that were carried out from 1996-2004, have now arrived in ES. These are Pseudophilatus rus (LC: least concern, IUCN category), Ps. hallidayi (VU) and Ramanella obscura; all these species are not threatened. If these species already occurred in Eastern Sinharaja prior to 2004, we should have found them, as they are common species where they occur (non threatened IUCN statuses also suggests this). However in 2005, Ps. rus was observed on the roadside to Morningside Bungalow; Ps. hallidayi was observed near Morningside Bunglow and R. obscura was observed in a regenerating forest patch; however at the time, their population size was low. By 2011, Ps. rus, was very common and occupied all habitat types; R. obscura and Ps. hallidayi were still a small population. In 2011, a dramatic drop of Taruga fastigo (CR), and Ps. decoris population was also observed.
The issues discussed and the trends delineated portend a bleak future for the Pseudophilautus and other endemic animals of ES. The entire Sinharaja, together with ES, provides a gradual gradient for animals to disperse, especially with climatic change. In the event of a warming event, mid-elevation species can migrate over to ES, if they are to track colder climates.
Thus the maintenance of this altitudinal habitat gradient is critically important for the conservation of both ES and lowland rainforest forms of Sinharaja. To ensure the non-establishment of invasive species, and to facilitate the ES endemic species, immediate action is needed to connect many of the scattered forest fragments through research driven reforestation programs. Activity, such as road building, encroachments, new plantations, which destroys connectivity in ES area should be minimized, while research activities and reforestation work is maximized. We have now started a long-term monitoring study in Morningside, which is being extended to an effort to restore critically important habitats.