Pact between predator and prey
ONCE upon a time, the beautiful blackbuck (Antelope cervicapra) lorded over the Velavadar National Park in Gujarat. But in the early '80s, the blackbuck's territorial sovereignty was challenged by a formidable enemy -- the wolf (Canis lupus pallipes). Earlier, the wolves had been casual visitors to the park; the past few years have seen them take residence and turn the blackbuck into their piece de resistance.
Although blackbuck now constitute over 80 per cent of a wolf's diet, a recent study by Yadvendradev V Jhala, a wildlife biologist at the Virginia Polytechnic Institute and State University, USA, reveals that the resident wolf pack and the blackbuck have now struck a congenial balance and can coexist (Conservation Biology, Vol 7, No 4). But he cautions that appropriate management of these two endangered species is essential if their populations in this 34 sq km park are to be maintained.
Jhala studied the feeding habits of the six-wolf pack from 1988 to 1990 and the impact this had on the population of other animals in the park. To discover the wolves' food habits, he looked for telltale signs like the hair and hooves of their prey in the wolves' stools. Apart from blackbuck, rodents and hares constituted a major part of the a wolf's diet.
Jhala found that one wolf killed about 35 blackbuck per year, whose annual multiplication was 25 per cent. He calculated that to sustain the pack of wolves, without jeopardising the blackbuck population, a total of at least 852 blackbuck would be required. This works out to at least 142 blackbuck per wolf. But in drought conditions -- which the study period encountered -- when blackbuck are stripped of flesh, Jhala reckons that as many as 171 blackbuck are needed per wolf, a total of 1,026 blackbuck. The total population of blackbuck during the study period, says Jhala, varied from 895 to 1,344 -- a safe range for a stable blackbuck population.
Jhala found that predation by wolves appears to keep blackbuck numbers in check, but other factors like the availability and quality of herbage for blackbuck also plays a role in regulating their numbers. Jhala found that blackbuck numbers placed a limit of 5.5 wolves in the park. He estimates that the park can accommodate at most a population of 1,710 blackbuck, which can sustain about 10 wolves.
Interestingly, Jhala found that the main management effort by the wildlife department -- keeping a check on the number of an exotic mesquite plant (Prosopis juliflora) by eradicating its saplings annually -- influenced the population of both blackbuck and wolves. Mesquite threatens to overrun the semi-arid grasslands and turn them into a thorn forest -- a habitat unsuitable for blackbuck. However, the plant also provides essential cover and denning for the wolves and should not be entirely eradicated.