Kruger National Park (South Africa) growth decline-ecology

Years of below-average rainfall in Kruger National Park (South Africa) cause a decline in the growth and productivity of grasses. Mortality rates in populations of herbivores such as the African buffalo then increase, resulting in a decline in population density. Based the information that you have been provided, would you conclude the annual variations in rainfall within Kruger function as a density-dependent mechanism regulating growth of the buffalo population? Explain. Is there any additional information that would cause you to change your answer?