AMPHIBIAN DIVERSITY AND THE CASE OF SRI LANKA ' S BURGEONING

Since the official implementation of zoological nomenclature by Carl von Linne in 1758 there has been a steady increase in the number of recognized extant amphibian species. However, rates of species descriptions over time have been neither constant nor decreasing as one would expect when assuming that the number of undiscovered species decreases with a longer period of scientific investigation. Unlike other, welf-known, vertebrate groups such as mammals and birds,, amphibians are 3 class where species numbers have increased exponentially, especially in recent decades (Glaw and Kohler 1998, AmphibiaWeb 2006). Since the early times of amphibian classification, the major works of a few active taxonomists contributed significantly to descriptions of novel taxa, specifically Josephus N. Laurenti, Frangois Daudin, Johann Baptist von Spix, Andre M. Constant Dumeri! and Gabriel Bibron, Albert C. L. G. Giinther, Edward D. Cope, Wilhelm Peters, George A. Boulenger and Oskar Boettger. With the increasing number of researchers dealing with the classification of amphibians and the intensified exploration of tropical regions, taxonomic work on amphibians experienced its first major boost and description rates of species per period steadily increased until the end of the 19 century. For example, about 260 species of amphibians were described in the last decade of the 19 century, many of which are still considered to represent valid taxa. Subseguently, a decrease in species description rates occurred during two periods of the last century. These periods correlate with the First and Second World Wars, respectively, with obviously low research activity (Glaw and Kohler 1998). However, the general long-term trend was still an increase in description rates. More recently, a second major boost of new species discoveries and descriptions has been in evidence. Whereas at the end of 1992, the number of amphibians recognized stood at only 4,533 species (Duellman 1993, Glaw etal. 1998), as of July 2006, this total stood at 6,041 species (AmphibiaWeb 2006). This eguates to an increase of more than 32% in only 13 years. The absolute number of newly described amphibian species per decade (not only the cumulative number of valid and described species) has been steadily increasing since the 1960s, with especially steep increases since the 1990s (Glaw and Kohler 1998, Kohler et al. 2005). No fewer than 810 amphibian species were described in the last decade of the 20 century; this is more than three times the number of species descriptions compared with the same period 100 years earlier. The average annual number of amphibians described during the 1990s was about 81 species; the number of described species in 2005 alone exceeds 200, a record that was never reached before. One factor contributing to this high rate of description was the publication of at least 35 new species from Sri Lanka (Manamendra-Arachi and Pethiyagoda 2005, Meegaskumbura and Manamendra-Arachi 2005). New species descriptions can be attributed, in part, to known populations of described species that have been found to be genetically or bioacoustically (in frogs) distinct, and may in many cases be recognized as different species. Modern molecular and bioacoustic technigues that provide increased 'resolution' have revealed that in many cases several morphologically similar, and hence, cryptic species may be concealed within a single taxon name. However, compared with true first-hand discoveries in amphibians, removal from synonymy constitutes a relatively small portion (-14%) of newly recognized species (Kohler et al 2005). Indeed, a large proportion of new species are genuine new discoveries, as exemplified by the recent spectacular findings of a new frog family, genus and species in India, the Nasikabatrachidae (Biju and Bossuyt 2003), and of a new genus and species of plethodontid salamander, Karsenia, in Korea the first Asian representative of this family (Min etal. 2005). A case study of mantellid frogs in Madagascar indicated that newly discovered species since 1990 were as genetically divergent as those described in previous research periods. Additionally, most had not been collected previously, indicating that the increase in new amphibian species on this island of endemism is not a sign of taxonomic inflation due to exaggerated splitting approaches or different species concepts (Kohler et al. 2005). If the current trend in species descriptions continues, we probably face a decade (2000-2009) in which more than 1,500 amphibian species could be described. This raises the interesting guestion of just how long will this trend continue and how many amphibian species are there on earth? Of course, nobody knows the final number and there is no available method to give an exact estimate. We suspect that at least several hundred new species remain to be described from throughout the tropical regions (including Madagascar, India, Sri Lanka, Indonesia, Philippines, New Guinea, and South America). For