Estimating abundance of Tibetan wild ass, Tibetan gazelle and Tibetan antelope using species distribution model and distance sampling

Abstract

There is an urgent need of understanding the distribution and abundance of the key species, Tibetan wild ass (Equus kiang), Tibetan gazelle (Procapra picticaudata) and Tibetan antelope (Pantholops hodgsonii) in the Three-River-Source National Park, especially after the first national park in China established there. We carried out field surveys in summers from 2014 to 2017 following the distance sampling protocol in the park, covering an area of 538000 km2. The total length of the survey routes is 14597.8 km. We recorded 3711 individuals of Tibetan wild ass, 1187 individuals of Tibetan gazelles, and 423 individuals of Tibetan antelopes. In order to accurately estimate the species abundance, we used species distribution models to quantify the relationship between species accurrences and 22 environmental variables, and predicted the population density in the whole study area. We compared the model prediction and field survey results, and made adjustment accordingly. The estimated abundance of Tibetan wild ass, Tibetan gazelle and Tibetan antelope in the study area is 44240, 13162, and 2390, respectively. To evaluate the potential bias of the estimation, we took into account of survey uncertainties, model uncertainties, and adjustment uncertainties using the detaction function based on distance sampling, R2 of species distribution models, and spatial heterogeneity of model-observation matchness. Our new method for estimating species abundance is suitable for species whose distribution is well correlated with environmental varibles, and the results of distance sampling are available.