Mountain endemism in Malesian geckos: can biotic interactions push lizards up hills?

Historical and contemporary processes shaping striking variation in terrestrial biodiversity along elevational gradients have received much attention from evolutionary biologists, often by way of comparisons to latitudinal environmental gradients. Here we synthetically review what is known of the diversity and origin of upland endemic geckos across the Malesian region (south-east Asia and Melanesia). Approximately 20% of the regional gecko fauna is endemic to mountains, but only around 8% have distributions centred on what we consider true montane habitats over 1000 metres above sea level. A majority of upland lineages lack close relatives in surrounding lowlands (although there are many exceptions) and some are highly phylogenetically divergent (e.g., estimated divergence from all other gecko taxa dating to the mid-Miocene or earlier). In several cases upland radiations are allied to other taxa centred on small islands or in disturbed lowland habitats, but absent or exceptionally rare in most lowland rainforest areas. A number of other upland lineages may have originated on smaller islands that are now merged into larger landmasses such as Sumatra and New Guinea. Based on often deep phylogenetic divergences, low community diversity and disjunct distributions across uplands and islands, we suggest that at least some upland lineages are more limited by biotic interactions than they are by climate. As global climates continue to warm in coming decades, such taxa may be particularly affected by upslope shifts of competitors and predators from lower elevations.