In contrast, a still unsolved biogeographic puzzle involves the differentiation of the Indochinese and Sundaic biotas without

any clear geological or geographic barrier. The position of this transition in forest-associated birds and its possible history near the Isthmus of Kra were discussed by Hughes et al. (2003) and Woodruff (2003a, b). Woodruff’s (2003a) hypothesis that the peninsula had been cut by barrier-like marine transgressions during the Neogene was not supported by subsequently revised global sea level curves (Miller et al. 2005; Lisiecki and Raymo 2005; Bintanja and van de Wal 2008; Naish and Wilson 2009) but dramatic sea level fluctuations may well account for today’s patterns. Woodruff and Turner (2009) hypothesized that the ~58 significant episodes of sea level rise (of >40 m) (Fig. 2a) and the flooding of the Sunda Shelf during the brief interglacial periods LY3023414 in vivo would have halved the habitat area available and forced the biota back repeatedly into refugia like those they are found in today. They suggested that the repeated 50–70% reduction in habitat area might account for the observed 30% reduction in mammal species diversity in the northern and central peninsula, and the observed clusters of species range limits north

and south of the area. The Indochinese-Sundaic transition in plants lies 500 km south of the Isthmus of Kra on the Kangar-Pattani Line and ecology rather than www.selleckchem.com/products/c646.html history has been used to explain its position (Fig. 1). Phytogeographers have hypothesized that this transition is associated with the occurrence of one or more months without rainfall north of the Kangar-Pattani Line (Whitmore 1998). Although maps of Weck’s selleck products Climatic Adenosine triphosphate Index show an abrupt change here (Brown et al. 2001), maps of the number of months with no significant rainfall suggest a more complex picture (see Wells 1999; Woodruff 2003a, b). The climatological underpinning of this ecological hypothesis needs to be verified, and van Steenis’ unpublished and

lost distribution maps of 1,200 plant genera should now be recreated. If, as it seems likely, some Malesian species occur at least 500 km further north of the Kangar-Pattani Line, where seasonal evergreen rainforest transitions to mixed moist deciduous forest near the Isthmus of Kra, then the plant transition will need reinterpretation (Woodruff 2003a, b). Today’s geography is highly unusual and recognizable for perhaps only 42 kyr or 2% of the last 2 Myr. It follows that today’s plant and animal species distribution patterns may also be unusual and <10 kyr old (Woodruff 2003a). For most of the last 2 Myr there was almost continuous dry land access between the continent and the islands of Sumatra, Java and Borneo. Land emerged whenever sea levels fell below −30 m; land bridges between the continent and today’s islands were the norm rather than the exception (Fig. 3b).