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Dryad

Mechanisms underlying altitudinal and horizontal range contraction: The western black crested gibbon

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Apr 15, 2022 version files 65.29 MB

Abstract

Aim: Species ranges in mountain areas may shift both horizontally and altitudinally, resulting from climate change and anthropogenic impact. Two hypotheses (the abundant center hypothesis and the contagion hypothesis) have been proposed to account for patterns of horizontal range contraction. However, undulating topograph causes a mosaic of unsuitable habitats, which may complicate the spatial pattern of range contraction. We develop a framework incorporating horizontal and altitudinal range contraction patterns of a species living in mountain areas, to better understand the underlying mechanisms of species range contraction.

Location: China, North Laos, and North Vietnam

Taxon: Western black crested gibbon, Nomascus concolor

Methods: We collected occurrence data of the gibbons from various sources and modelled their potential distribution range in the 1950s, 1980s, and 2010s, using ecological niche modelling. We compared distances from the center point of the potential range in 1950s to center points of the largest 100 patches in the 1950s and the 2010s to understand the patterns of horizontal range contraction. We also calculated potential distribution within different altitudinal range for six populations in each period to understand the patterns of altitudinal range contraction.

Results: Potential horizontal distribution of the gibbons decreased by 69% from the 1950s to the 2010s. We found the 100 largest patches in 2010s were further apart from the center point of the potential range in 1950s compared to the 100 largest patches in 1950s, supporting the contagion hypothesis. No populations extended their range to higher altitude, suggesting climate change did not have a profound effect on gibbon range upward shift. All populations lost a substantial proportion of their ranges in lower altitude (500 – 1,500 m) but to different degrees, suggesting that populations experienced different anthropogenic pressures.

Main conclusions: Anthropogenic threats probably including human population increase, agricultural expansion and hunting, were more likely than climate change to have caused range contraction in western black-crested gibbons. This study highlights the importance of studying horizontal and altitudinal range contraction simultaneously.