Ecological Niche Conservatism in Doucs (Genus Pygathrix)

Abstract

The impressive diversity and unique distribution of primate taxa in Southeast Asia creates a region of interesting biogeography and evolutionary history that remains poorly understood. The three species in the Asian colobine genus Pygathrix (P. cinerea, P. nemaeus, and P. nigripes) appear to follow the unique distribution pattern, replacing one another along the north-south axis. However, the evolutionary history and taxonomic status within Pygathrix is currently debated. We constructed climate-based ecological niche models (ENMs) for the three species, using six environmental variables, to confirm that the bioclimate envelopes of Pygathrix cinerea, P. nemaeus, and P. nigripes follow the north-south gradient. We also used the ENMs to test whether the three species lack ecological exchangeability, meaning differentiation among factors that define the fundamental niche, and whether they exhibit ecological niche conservatism, or the tendency for related species to differ less ecologically than might be expected by the climate available to each species. Our ENMs for Pygathrix followed a north-south gradient as expected, with P. nemaeus extending from ca. 14°N to 21°N, P. cinerea from 14°N to 16°N, and P. nigripes from 11°N to 13.5°N. This study presents the first use of ENMs for doucs that yield Int J Primatol (2012) 33:972-988 significant predictive ability based only on climatic variables. The models are significantly different for all three species, supporting a lack of ecological exchangeability between them, as well as the recent elevation of Pygathrix cinerea to species status. Importantly, Pygathrix cinerea and P. nemaeus show evidence of ecological niche conservatism, which lends support to the occurrence of an allopatric speciation event. This result also suggests that the current overlapping distribution of Pygathrix cinerea and P. nemaeus is the result of secondary contact. The north-south distribution gradient, which exists in similar form among other groups of sister taxa in the region, may be attributed to a zoogeographic barrier, vicariance, or current or historical climatic shifts.

Predicting Suitable Distribution for an Endemic, Rare and Threatened Species (Grey-Shanked Douc Langur, Pygathrix Cinerea Nadler, 1997) Using Maxent Model

“…In the predictive distribution model of GSDL, precipitation of the driest month (bio14) has the highest effect of all parameters. This is in line with the findings of (Bett et al, 2012). In the South Central and Central Highland regions of Vietnam, climate features vary immensely.…”

“…Then, the temperature annual range (bio7) was the second one with 18.3%. The total suitable area of GSDL is 16,680.52 km 2 . The least suitable area accounts for about 42% of the total area.…”

“…Furthermore, climate biology features are also thought to affect the distribution of species in Pygathrix ssp. (Bett et al, 2012). The use of climate variables is an effective way of identifying geographical distributions of species (Sarmar et al, 2015).…”

“…ENMs is often used for the following purposes: (1) assessing/ estimating suitable habitat for species; (2) assessing changes in species distribution over time based on scenarios of changes in environmental conditions; (3) assessing ecological niches or ecological requirements of species (Warren and Seifert, 2011). The accuracy of the predicted results depends on a number of factors such as the complexity and accuracy of the models, the environmental data layers, and the species distribution data .…”

“…Recently, new populations of GSDL are still being discovered (FFI, 2016), therefore, investigating the presence of the species in the areas that have not been surveyed before is necessary. Bett et al (2012) modelled the distribution of the three species in the Pygathrix genus, however, vegetation and terrain-related variables were not used. Variables related to vegetation and terrain have been shown to be important in modelling the distribution of mammal species (Cork and Catling, 1996), especially for Pygathrix because these species only feeds on plants and move predominately in canopy.…”