Overgrazing effects on seasonal variations in availability of palatable grasses in the foraging grounds of blackbucks Antilope cervicapra

Abstract

Despite the diverse and wide-ranging forage availability in abundance in grassland habitat systems, wild ungulates perform selective grazing under their natural foraging conditions as an adaptation to the variation in palatability and availability of forage grasses in different seasons in a given area by retaining the less palatable species as the dry season diet. The study elucidated how the domestic livestock exerts overgrazing pressures on the grass community, removing all the grass stand before the arrival of dry season and restricting forage availability for blackbucks Antilope cervicapra in Basur Amruth Mahal Kaval Conservation Reserve, Karnataka. Direct observations on the feeding behaviours of herbivores were done and opportunistic sampling for the collection and identification of grasses at the same time, covering all different microhabitat characteristic locations of the grassland in all seasons. 29 grass species were identified with different palatability grades and variations in their seasonal availability as forage. Dichanthium annulatum (Forssk.) Stapf and Sehima nervosum (Rottler) Stapf with the highest palatability grade, are spatially declining with the increase of less palatable grasses in the Kaval i.e. Heteropogon contortus (L.) P.Beauv. ex Roem. & Schult. and Chrysopogon fulvus (Spreng.) Chiov under overgrazing pressures. A limitation of three to four months shortage of forage grass availability was created under overgrazing pressures by domestic livestock when compared to selective grazing expectations by blackbucks throughout the year. The forage grasses were grazed to empty by domestic livestock before the arrival of dry seasons. In prolonged overgrazing effects, a competitive replacement of palatable grasses by unpalatable or less palatable species can be expected in these grasslands. Competitive exclusion of blackbucks by the domestic herbivores was modelled using Lotka-Volterra equations. The model revealed that the populations of wild boar and domestic herbivores tend to increase up to their carrying capacities K2 with time ti and attain stable populations, but the blackbuck populations tend to extinction with continuous exposure to competition due to their shy nature. The grass composition can be expected to recover with palatable grasses only if external grazing forces are controlled or avoided.