Influence of invasive Prosopis juliflora on the distribution and ecology of native blackbuck in protected areas of Tamil Nadu, India

Baseline data on intrinsic-extrinsic determinants of spatial distribution of flagship species helps wildlife managers develop their management strategies. Globally, large herbivores are in range contraction due to the expansion of human habitation. Of late, alien invasion is raising management concerns due to its detrimental effect on native biota. This study evaluating the determinants of spatial detectability and density distribution of blackbuck Antilope cervicapra, an endemic species of the Indian subcontinent, demonstrates the negative influence of Prosopis juliflora, an alien invasive, on the native blackbuck at three reserves-Point Calimere Wildlife Sanctuary, Guindy National Park and Sathyamangalam Tiger Reserve, Tamil Nadu, India. Using distance sampling technique, the study has surveyed blackbuck from 26 grid-based, spatially replicated line-transects between January 2018 and July 2019. Furthermore, 27 covariates related to climate, habitat and anthropogenic pressure were evaluated to determine their effect on spatial detectability and density distribution. Regression by Empirical Variable Selection showed that blackbuck spatial detectability and density distribution increase significantly with the extent of grassland, habitat openness and grass biomass, but decreases with Prosopis cover, shrub cover, percentage of woodland and distance to water, thus revealing their negative effect on the blackbuck. Besides, the Prosopis cover also decreases significantly the key positive predictors of the density distribution of blackbuck, namely the extent of grassland, habitat openness and grass productivity. Thus, the study concludes that the alien invasive species has a negative effect on the native blackbuck population. This raises the need for controlling or eliminating the invasive species in order to conserve, in the long run, the endemic blackbuck at the three reserves.